Merge github.com:grpc/grpc into serve_fries

110 files changed, 8068 insertions, 556 deletions

diff --git a/src/core/ext/filters/client_channel/channel_connectivity.c b/src/core/ext/filters/client_channel/channel_connectivity.c
index 62f58fb278..f83670db82 100644
--- a/src/core/ext/filters/client_channel/channel_connectivity.c
+++ b/src/core/ext/filters/client_channel/channel_connectivity.c
@@ -132,7 +132,7 @@ static void partly_done(grpc_exec_ctx *exec_ctx, state_watcher *w,
   gpr_mu_lock(&w->mu);
 
   if (due_to_completion) {
-    if (grpc_trace_operation_failures) {
+    if (GRPC_TRACER_ON(grpc_trace_operation_failures)) {
       GRPC_LOG_IF_ERROR("watch_completion_error", GRPC_ERROR_REF(error));
     }
     GRPC_ERROR_UNREF(error);
diff --git a/src/core/ext/filters/client_channel/client_channel.c b/src/core/ext/filters/client_channel/client_channel.c
index 0463b25412..24843d52e9 100644
--- a/src/core/ext/filters/client_channel/client_channel.c
+++ b/src/core/ext/filters/client_channel/client_channel.c
@@ -760,12 +760,6 @@ static void cc_destroy_channel_elem(grpc_exec_ctx *exec_ctx,
 
 #define CANCELLED_CALL ((grpc_subchannel_call *)1)
 
-typedef enum {
-  /* zero so that it can be default-initialized */
-  GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING = 0,
-  GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL
-} subchannel_creation_phase;
-
 /** Call data.  Holds a pointer to grpc_subchannel_call and the
     associated machinery to create such a pointer.
     Handles queueing of stream ops until a call object is ready, waiting
@@ -793,8 +787,9 @@ typedef struct client_channel_call_data {
   gpr_atm subchannel_call;
   gpr_arena *arena;
 
-  subchannel_creation_phase creation_phase;
+  bool pick_pending;
   grpc_connected_subchannel *connected_subchannel;
+  grpc_call_context_element subchannel_call_context[GRPC_CONTEXT_COUNT];
   grpc_polling_entity *pollent;
 
   grpc_transport_stream_op_batch **waiting_ops;
@@ -914,11 +909,10 @@ static void subchannel_ready_locked(grpc_exec_ctx *exec_ctx, void *arg,
   grpc_call_element *elem = arg;
   call_data *calld = elem->call_data;
   channel_data *chand = elem->channel_data;
-  GPR_ASSERT(calld->creation_phase ==
-             GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL);
+  GPR_ASSERT(calld->pick_pending);
+  calld->pick_pending = false;
   grpc_polling_entity_del_from_pollset_set(exec_ctx, calld->pollent,
                                            chand->interested_parties);
-  calld->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
   if (calld->connected_subchannel == NULL) {
     gpr_atm_no_barrier_store(&calld->subchannel_call, 1);
     fail_locked(exec_ctx, calld,
@@ -944,7 +938,8 @@ static void subchannel_ready_locked(grpc_exec_ctx *exec_ctx, void *arg,
         .path = calld->path,
         .start_time = calld->call_start_time,
         .deadline = calld->deadline,
-        .arena = calld->arena};
+        .arena = calld->arena,
+        .context = calld->subchannel_call_context};
     grpc_error *new_error = grpc_connected_subchannel_create_call(
         exec_ctx, calld->connected_subchannel, &call_args, &subchannel_call);
     gpr_atm_rel_store(&calld->subchannel_call,
@@ -973,6 +968,7 @@ typedef struct {
   grpc_metadata_batch *initial_metadata;
   uint32_t initial_metadata_flags;
   grpc_connected_subchannel **connected_subchannel;
+  grpc_call_context_element *subchannel_call_context;
   grpc_closure *on_ready;
   grpc_call_element *elem;
   grpc_closure closure;
@@ -984,8 +980,8 @@ typedef struct {
 static bool pick_subchannel_locked(
     grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
     grpc_metadata_batch *initial_metadata, uint32_t initial_metadata_flags,
-    grpc_connected_subchannel **connected_subchannel, grpc_closure *on_ready,
-    grpc_error *error);
+    grpc_connected_subchannel **connected_subchannel,
+    grpc_call_context_element *subchannel_call_context, grpc_closure *on_ready);
 
 static void continue_picking_locked(grpc_exec_ctx *exec_ctx, void *arg,
                                     grpc_error *error) {
@@ -997,49 +993,49 @@ static void continue_picking_locked(grpc_exec_ctx *exec_ctx, void *arg,
   } else {
     if (pick_subchannel_locked(exec_ctx, cpa->elem, cpa->initial_metadata,
                                cpa->initial_metadata_flags,
-                               cpa->connected_subchannel, cpa->on_ready,
-                               GRPC_ERROR_NONE)) {
+                               cpa->connected_subchannel,
+                               cpa->subchannel_call_context, cpa->on_ready)) {
       grpc_closure_sched(exec_ctx, cpa->on_ready, GRPC_ERROR_NONE);
     }
   }
   gpr_free(cpa);
 }
 
+static void cancel_pick_locked(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                               grpc_error *error) {
+  channel_data *chand = elem->channel_data;
+  call_data *calld = elem->call_data;
+  if (chand->lb_policy != NULL) {
+    grpc_lb_policy_cancel_pick_locked(exec_ctx, chand->lb_policy,
+                                      &calld->connected_subchannel,
+                                      GRPC_ERROR_REF(error));
+  }
+  for (grpc_closure *closure = chand->waiting_for_config_closures.head;
+       closure != NULL; closure = closure->next_data.next) {
+    continue_picking_args *cpa = closure->cb_arg;
+    if (cpa->connected_subchannel == &calld->connected_subchannel) {
+      cpa->connected_subchannel = NULL;
+      grpc_closure_sched(exec_ctx, cpa->on_ready,
+                         GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
+                             "Pick cancelled", &error, 1));
+    }
+  }
+  GRPC_ERROR_UNREF(error);
+}
+
 static bool pick_subchannel_locked(
     grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
     grpc_metadata_batch *initial_metadata, uint32_t initial_metadata_flags,
-    grpc_connected_subchannel **connected_subchannel, grpc_closure *on_ready,
-    grpc_error *error) {
+    grpc_connected_subchannel **connected_subchannel,
+    grpc_call_context_element *subchannel_call_context,
+    grpc_closure *on_ready) {
   GPR_TIMER_BEGIN("pick_subchannel", 0);
 
   channel_data *chand = elem->channel_data;
   call_data *calld = elem->call_data;
-  continue_picking_args *cpa;
-  grpc_closure *closure;
 
   GPR_ASSERT(connected_subchannel);
 
-  if (initial_metadata == NULL) {
-    if (chand->lb_policy != NULL) {
-      grpc_lb_policy_cancel_pick_locked(exec_ctx, chand->lb_policy,
-                                        connected_subchannel,
-                                        GRPC_ERROR_REF(error));
-    }
-    for (closure = chand->waiting_for_config_closures.head; closure != NULL;
-         closure = closure->next_data.next) {
-      cpa = closure->cb_arg;
-      if (cpa->connected_subchannel == connected_subchannel) {
-        cpa->connected_subchannel = NULL;
-        grpc_closure_sched(exec_ctx, cpa->on_ready,
-                           GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
-                               "Pick cancelled", &error, 1));
-      }
-    }
-    GPR_TIMER_END("pick_subchannel", 0);
-    GRPC_ERROR_UNREF(error);
-    return true;
-  }
-  GPR_ASSERT(error == GRPC_ERROR_NONE);
   if (chand->lb_policy != NULL) {
     apply_final_configuration_locked(exec_ctx, elem);
     grpc_lb_policy *lb_policy = chand->lb_policy;
@@ -1062,8 +1058,7 @@ static bool pick_subchannel_locked(
       }
     }
     const grpc_lb_policy_pick_args inputs = {
-        initial_metadata, initial_metadata_flags, &calld->lb_token_mdelem,
-        gpr_inf_future(GPR_CLOCK_MONOTONIC)};
+        initial_metadata, initial_metadata_flags, &calld->lb_token_mdelem};
 
     // Wrap the user-provided callback in order to hold a strong reference to
     // the LB policy for the duration of the pick.
@@ -1076,8 +1071,8 @@ static bool pick_subchannel_locked(
     GRPC_LB_POLICY_REF(lb_policy, "pick_subchannel_wrapping");
     w_on_pick_arg->lb_policy = lb_policy;
     const bool pick_done = grpc_lb_policy_pick_locked(
-        exec_ctx, lb_policy, &inputs, connected_subchannel, NULL,
-        &w_on_pick_arg->wrapper_closure);
+        exec_ctx, lb_policy, &inputs, connected_subchannel,
+        subchannel_call_context, NULL, &w_on_pick_arg->wrapper_closure);
     if (pick_done) {
       /* synchronous grpc_lb_policy_pick call. Unref the LB policy. */
       GRPC_LB_POLICY_UNREF(exec_ctx, w_on_pick_arg->lb_policy,
@@ -1096,10 +1091,11 @@ static bool pick_subchannel_locked(
                               &chand->on_resolver_result_changed);
   }
   if (chand->resolver != NULL) {
-    cpa = gpr_malloc(sizeof(*cpa));
+    continue_picking_args *cpa = gpr_malloc(sizeof(*cpa));
     cpa->initial_metadata = initial_metadata;
     cpa->initial_metadata_flags = initial_metadata_flags;
     cpa->connected_subchannel = connected_subchannel;
+    cpa->subchannel_call_context = subchannel_call_context;
     cpa->on_ready = on_ready;
     cpa->elem = elem;
     grpc_closure_init(&cpa->closure, continue_picking_locked, cpa,
@@ -1151,16 +1147,13 @@ static void start_transport_stream_op_batch_locked_inner(
          error to the caller when the first op does get passed down. */
       calld->cancel_error =
           GRPC_ERROR_REF(op->payload->cancel_stream.cancel_error);
-      switch (calld->creation_phase) {
-        case GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING:
-          fail_locked(exec_ctx, calld,
-                      GRPC_ERROR_REF(op->payload->cancel_stream.cancel_error));
-          break;
-        case GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL:
-          pick_subchannel_locked(
-              exec_ctx, elem, NULL, 0, &calld->connected_subchannel, NULL,
-              GRPC_ERROR_REF(op->payload->cancel_stream.cancel_error));
-          break;
+      if (calld->pick_pending) {
+        cancel_pick_locked(
+            exec_ctx, elem,
+            GRPC_ERROR_REF(op->payload->cancel_stream.cancel_error));
+      } else {
+        fail_locked(exec_ctx, calld,
+                    GRPC_ERROR_REF(op->payload->cancel_stream.cancel_error));
       }
       grpc_transport_stream_op_batch_finish_with_failure(
           exec_ctx, op,
@@ -1170,9 +1163,9 @@ static void start_transport_stream_op_batch_locked_inner(
     }
   }
   /* if we don't have a subchannel, try to get one */
-  if (calld->creation_phase == GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING &&
-      calld->connected_subchannel == NULL && op->send_initial_metadata) {
-    calld->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL;
+  if (!calld->pick_pending && calld->connected_subchannel == NULL &&
+      op->send_initial_metadata) {
+    calld->pick_pending = true;
     grpc_closure_init(&calld->next_step, subchannel_ready_locked, elem,
                       grpc_combiner_scheduler(chand->combiner, true));
     GRPC_CALL_STACK_REF(calld->owning_call, "pick_subchannel");
@@ -1183,8 +1176,9 @@ static void start_transport_stream_op_batch_locked_inner(
             exec_ctx, elem,
             op->payload->send_initial_metadata.send_initial_metadata,
             op->payload->send_initial_metadata.send_initial_metadata_flags,
-            &calld->connected_subchannel, &calld->next_step, GRPC_ERROR_NONE)) {
-      calld->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
+            &calld->connected_subchannel, calld->subchannel_call_context,
+            &calld->next_step)) {
+      calld->pick_pending = false;
       GRPC_CALL_STACK_UNREF(exec_ctx, calld->owning_call, "pick_subchannel");
     } else {
       grpc_polling_entity_add_to_pollset_set(exec_ctx, calld->pollent,
@@ -1192,15 +1186,15 @@ static void start_transport_stream_op_batch_locked_inner(
     }
   }
   /* if we've got a subchannel, then let's ask it to create a call */
-  if (calld->creation_phase == GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING &&
-      calld->connected_subchannel != NULL) {
+  if (!calld->pick_pending && calld->connected_subchannel != NULL) {
     grpc_subchannel_call *subchannel_call = NULL;
     const grpc_connected_subchannel_call_args call_args = {
         .pollent = calld->pollent,
         .path = calld->path,
         .start_time = calld->call_start_time,
         .deadline = calld->deadline,
-        .arena = calld->arena};
+        .arena = calld->arena,
+        .context = calld->subchannel_call_context};
     grpc_error *error = grpc_connected_subchannel_create_call(
         exec_ctx, calld->connected_subchannel, &call_args, &subchannel_call);
     gpr_atm_rel_store(&calld->subchannel_call,
@@ -1349,12 +1343,18 @@ static void cc_destroy_call_elem(grpc_exec_ctx *exec_ctx,
     then_schedule_closure = NULL;
     GRPC_SUBCHANNEL_CALL_UNREF(exec_ctx, call, "client_channel_destroy_call");
   }
-  GPR_ASSERT(calld->creation_phase == GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING);
+  GPR_ASSERT(!calld->pick_pending);
   GPR_ASSERT(calld->waiting_ops_count == 0);
   if (calld->connected_subchannel != NULL) {
     GRPC_CONNECTED_SUBCHANNEL_UNREF(exec_ctx, calld->connected_subchannel,
                                     "picked");
   }
+  for (size_t i = 0; i < GRPC_CONTEXT_COUNT; ++i) {
+    if (calld->subchannel_call_context[i].value != NULL) {
+      calld->subchannel_call_context[i].destroy(
+          calld->subchannel_call_context[i].value);
+    }
+  }
   gpr_free(calld->waiting_ops);
   grpc_closure_sched(exec_ctx, then_schedule_closure, GRPC_ERROR_NONE);
 }
@@ -1450,12 +1450,12 @@ static void watch_connectivity_state_locked(grpc_exec_ctx *exec_ctx, void *arg,
 
 void grpc_client_channel_watch_connectivity_state(
     grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, grpc_pollset *pollset,
-    grpc_connectivity_state *state, grpc_closure *on_complete) {
+    grpc_connectivity_state *state, grpc_closure *closure) {
   channel_data *chand = elem->channel_data;
   external_connectivity_watcher *w = gpr_malloc(sizeof(*w));
   w->chand = chand;
   w->pollset = pollset;
-  w->on_complete = on_complete;
+  w->on_complete = closure;
   w->state = state;
   grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties, pollset);
   GRPC_CHANNEL_STACK_REF(w->chand->owning_stack,
diff --git a/src/core/ext/filters/client_channel/lb_policy.c b/src/core/ext/filters/client_channel/lb_policy.c
index 2d31499d13..112ba40658 100644
--- a/src/core/ext/filters/client_channel/lb_policy.c
+++ b/src/core/ext/filters/client_channel/lb_policy.c
@@ -119,9 +119,10 @@ void grpc_lb_policy_weak_unref(grpc_exec_ctx *exec_ctx,
 int grpc_lb_policy_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                                const grpc_lb_policy_pick_args *pick_args,
                                grpc_connected_subchannel **target,
+                               grpc_call_context_element *context,
                                void **user_data, grpc_closure *on_complete) {
   return policy->vtable->pick_locked(exec_ctx, policy, pick_args, target,
-                                     user_data, on_complete);
+                                     context, user_data, on_complete);
 }
 
 void grpc_lb_policy_cancel_pick_locked(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/ext/filters/client_channel/lb_policy.h b/src/core/ext/filters/client_channel/lb_policy.h
index 25427666ae..184b2ef720 100644
--- a/src/core/ext/filters/client_channel/lb_policy.h
+++ b/src/core/ext/filters/client_channel/lb_policy.h
@@ -43,9 +43,6 @@
 typedef struct grpc_lb_policy grpc_lb_policy;
 typedef struct grpc_lb_policy_vtable grpc_lb_policy_vtable;
 
-typedef void (*grpc_lb_completion)(void *cb_arg, grpc_subchannel *subchannel,
-                                   grpc_status_code status, const char *errmsg);
-
 struct grpc_lb_policy {
   const grpc_lb_policy_vtable *vtable;
   gpr_atm ref_pair;
@@ -65,8 +62,6 @@ typedef struct grpc_lb_policy_pick_args {
   uint32_t initial_metadata_flags;
   /** Storage for LB token in \a initial_metadata, or NULL if not used */
   grpc_linked_mdelem *lb_token_mdelem_storage;
-  /** Deadline for the call to the LB server */
-  gpr_timespec deadline;
 } grpc_lb_policy_pick_args;
 
 struct grpc_lb_policy_vtable {
@@ -76,7 +71,8 @@ struct grpc_lb_policy_vtable {
   /** \see grpc_lb_policy_pick */
   int (*pick_locked)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                      const grpc_lb_policy_pick_args *pick_args,
-                     grpc_connected_subchannel **target, void **user_data,
+                     grpc_connected_subchannel **target,
+                     grpc_call_context_element *context, void **user_data,
                      grpc_closure *on_complete);
 
   /** \see grpc_lb_policy_cancel_pick */
@@ -156,6 +152,8 @@ void grpc_lb_policy_init(grpc_lb_policy *policy,
     \a target will be set to the selected subchannel, or NULL on failure.
     Upon success, \a user_data will be set to whatever opaque information
     may need to be propagated from the LB policy, or NULL if not needed.
+    \a context will be populated with context to pass to the subchannel
+    call, if needed.
 
     If the pick succeeds and a result is known immediately, a non-zero
     value will be returned.  Otherwise, \a on_complete will be invoked
@@ -167,6 +165,7 @@ void grpc_lb_policy_init(grpc_lb_policy *policy,
 int grpc_lb_policy_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                                const grpc_lb_policy_pick_args *pick_args,
                                grpc_connected_subchannel **target,
+                               grpc_call_context_element *context,
                                void **user_data, grpc_closure *on_complete);
 
 /** Perform a connected subchannel ping (see \a grpc_connected_subchannel_ping)
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.c b/src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.c
new file mode 100644
index 0000000000..67baa46de7
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.c
@@ -0,0 +1,153 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.h"
+
+#include <grpc/support/atm.h>
+#include <grpc/support/log.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h"
+#include "src/core/lib/iomgr/error.h"
+#include "src/core/lib/profiling/timers.h"
+
+static grpc_error *init_channel_elem(grpc_exec_ctx *exec_ctx,
+                                     grpc_channel_element *elem,
+                                     grpc_channel_element_args *args) {
+  return GRPC_ERROR_NONE;
+}
+
+static void destroy_channel_elem(grpc_exec_ctx *exec_ctx,
+                                 grpc_channel_element *elem) {}
+
+typedef struct {
+  // Stats object to update.
+  grpc_grpclb_client_stats *client_stats;
+  // State for intercepting send_initial_metadata.
+  grpc_closure on_complete_for_send;
+  grpc_closure *original_on_complete_for_send;
+  bool send_initial_metadata_succeeded;
+  // State for intercepting recv_initial_metadata.
+  grpc_closure recv_initial_metadata_ready;
+  grpc_closure *original_recv_initial_metadata_ready;
+  bool recv_initial_metadata_succeeded;
+} call_data;
+
+static void on_complete_for_send(grpc_exec_ctx *exec_ctx, void *arg,
+                                 grpc_error *error) {
+  call_data *calld = arg;
+  if (error == GRPC_ERROR_NONE) {
+    calld->send_initial_metadata_succeeded = true;
+  }
+  grpc_closure_run(exec_ctx, calld->original_on_complete_for_send,
+                   GRPC_ERROR_REF(error));
+}
+
+static void recv_initial_metadata_ready(grpc_exec_ctx *exec_ctx, void *arg,
+                                        grpc_error *error) {
+  call_data *calld = arg;
+  if (error == GRPC_ERROR_NONE) {
+    calld->recv_initial_metadata_succeeded = true;
+  }
+  grpc_closure_run(exec_ctx, calld->original_recv_initial_metadata_ready,
+                   GRPC_ERROR_REF(error));
+}
+
+static grpc_error *init_call_elem(grpc_exec_ctx *exec_ctx,
+                                  grpc_call_element *elem,
+                                  const grpc_call_element_args *args) {
+  call_data *calld = elem->call_data;
+  // Get stats object from context and take a ref.
+  GPR_ASSERT(args->context != NULL);
+  GPR_ASSERT(args->context[GRPC_GRPCLB_CLIENT_STATS].value != NULL);
+  calld->client_stats = grpc_grpclb_client_stats_ref(
+      args->context[GRPC_GRPCLB_CLIENT_STATS].value);
+  // Record call started.
+  grpc_grpclb_client_stats_add_call_started(calld->client_stats);
+  return GRPC_ERROR_NONE;
+}
+
+static void destroy_call_elem(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+                              const grpc_call_final_info *final_info,
+                              grpc_closure *ignored) {
+  call_data *calld = elem->call_data;
+  // Record call finished, optionally setting client_failed_to_send and
+  // received.
+  grpc_grpclb_client_stats_add_call_finished(
+      false /* drop_for_rate_limiting */, false /* drop_for_load_balancing */,
+      !calld->send_initial_metadata_succeeded /* client_failed_to_send */,
+      calld->recv_initial_metadata_succeeded /* known_received */,
+      calld->client_stats);
+  // All done, so unref the stats object.
+  grpc_grpclb_client_stats_unref(calld->client_stats);
+}
+
+static void start_transport_stream_op_batch(
+    grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+    grpc_transport_stream_op_batch *batch) {
+  call_data *calld = elem->call_data;
+  GPR_TIMER_BEGIN("clr_start_transport_stream_op_batch", 0);
+  // Intercept send_initial_metadata.
+  if (batch->send_initial_metadata) {
+    calld->original_on_complete_for_send = batch->on_complete;
+    grpc_closure_init(&calld->on_complete_for_send, on_complete_for_send, calld,
+                      grpc_schedule_on_exec_ctx);
+    batch->on_complete = &calld->on_complete_for_send;
+  }
+  // Intercept recv_initial_metadata.
+  if (batch->recv_initial_metadata) {
+    calld->original_recv_initial_metadata_ready =
+        batch->payload->recv_initial_metadata.recv_initial_metadata_ready;
+    grpc_closure_init(&calld->recv_initial_metadata_ready,
+                      recv_initial_metadata_ready, calld,
+                      grpc_schedule_on_exec_ctx);
+    batch->payload->recv_initial_metadata.recv_initial_metadata_ready =
+        &calld->recv_initial_metadata_ready;
+  }
+  // Chain to next filter.
+  grpc_call_next_op(exec_ctx, elem, batch);
+  GPR_TIMER_END("clr_start_transport_stream_op_batch", 0);
+}
+
+const grpc_channel_filter grpc_client_load_reporting_filter = {
+    start_transport_stream_op_batch,
+    grpc_channel_next_op,
+    sizeof(call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset_or_pollset_set,
+    destroy_call_elem,
+    0,  // sizeof(channel_data)
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    grpc_channel_next_get_info,
+    "client_load_reporting"};
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.h b/src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.h
new file mode 100644
index 0000000000..28b313d874
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.h
@@ -0,0 +1,42 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_GRPCLB_CLIENT_LOAD_REPORTING_FILTER_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_GRPCLB_CLIENT_LOAD_REPORTING_FILTER_H
+
+#include "src/core/lib/channel/channel_stack.h"
+
+extern const grpc_channel_filter grpc_client_load_reporting_filter;
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_GRPCLB_CLIENT_LOAD_REPORTING_FILTER_H \
+          */
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.c b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.c
index ad5f0685ec..b7c0e929b7 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.c
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.c
@@ -95,8 +95,7 @@
    headers. Therefore, sockaddr.h must always be included first */
 #include "src/core/lib/iomgr/sockaddr.h"
 
-#include <errno.h>
-
+#include <limits.h>
 #include <string.h>
 
 #include <grpc/byte_buffer_reader.h>
@@ -108,13 +107,16 @@
 
 #include "src/core/ext/filters/client_channel/client_channel.h"
 #include "src/core/ext/filters/client_channel/client_channel_factory.h"
+#include "src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.h"
 #include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.h"
 #include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_channel.h"
+#include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h"
 #include "src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.h"
 #include "src/core/ext/filters/client_channel/lb_policy_factory.h"
 #include "src/core/ext/filters/client_channel/lb_policy_registry.h"
 #include "src/core/ext/filters/client_channel/parse_address.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/sockaddr.h"
 #include "src/core/lib/iomgr/sockaddr_utils.h"
@@ -126,6 +128,7 @@
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/surface/call.h"
 #include "src/core/lib/surface/channel.h"
+#include "src/core/lib/surface/channel_init.h"
 #include "src/core/lib/transport/static_metadata.h"
 
 #define GRPC_GRPCLB_MIN_CONNECT_TIMEOUT_SECONDS 20
@@ -134,7 +137,7 @@
 #define GRPC_GRPCLB_RECONNECT_MAX_BACKOFF_SECONDS 120
 #define GRPC_GRPCLB_RECONNECT_JITTER 0.2
 
-int grpc_lb_glb_trace = 0;
+grpc_tracer_flag grpc_lb_glb_trace = GRPC_TRACER_INITIALIZER(false);
 
 /* add lb_token of selected subchannel (address) to the call's initial
  * metadata */
@@ -147,6 +150,10 @@ static grpc_error *initial_metadata_add_lb_token(
                                       lb_token_mdelem_storage, lb_token);
 }
 
+static void destroy_client_stats(void *arg) {
+  grpc_grpclb_client_stats_unref(arg);
+}
+
 typedef struct wrapped_rr_closure_arg {
   /* the closure instance using this struct as argument */
   grpc_closure wrapper_closure;
@@ -163,6 +170,13 @@ typedef struct wrapped_rr_closure_arg {
    * initial metadata */
   grpc_connected_subchannel **target;
 
+  /* the context to be populated for the subchannel call */
+  grpc_call_context_element *context;
+
+  /* Stats for client-side load reporting. Note that this holds a
+   * reference, which must be either passed on via context or unreffed. */
+  grpc_grpclb_client_stats *client_stats;
+
   /* the LB token associated with the pick */
   grpc_mdelem lb_token;
 
@@ -202,8 +216,14 @@ static void wrapped_rr_closure(grpc_exec_ctx *exec_ctx, void *arg,
                 (void *)*wc_arg->target, (void *)wc_arg->rr_policy);
         abort();
       }
+      // Pass on client stats via context. Passes ownership of the reference.
+      GPR_ASSERT(wc_arg->client_stats != NULL);
+      wc_arg->context[GRPC_GRPCLB_CLIENT_STATS].value = wc_arg->client_stats;
+      wc_arg->context[GRPC_GRPCLB_CLIENT_STATS].destroy = destroy_client_stats;
+    } else {
+      grpc_grpclb_client_stats_unref(wc_arg->client_stats);
     }
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO, "Unreffing RR %p", (void *)wc_arg->rr_policy);
     }
     GRPC_LB_POLICY_UNREF(exec_ctx, wc_arg->rr_policy, "wrapped_rr_closure");
@@ -237,6 +257,7 @@ typedef struct pending_pick {
 static void add_pending_pick(pending_pick **root,
                              const grpc_lb_policy_pick_args *pick_args,
                              grpc_connected_subchannel **target,
+                             grpc_call_context_element *context,
                              grpc_closure *on_complete) {
   pending_pick *pp = gpr_zalloc(sizeof(*pp));
   pp->next = *root;
@@ -244,6 +265,7 @@ static void add_pending_pick(pending_pick **root,
   pp->target = target;
   pp->wrapped_on_complete_arg.wrapped_closure = on_complete;
   pp->wrapped_on_complete_arg.target = target;
+  pp->wrapped_on_complete_arg.context = context;
   pp->wrapped_on_complete_arg.initial_metadata = pick_args->initial_metadata;
   pp->wrapped_on_complete_arg.lb_token_mdelem_storage =
       pick_args->lb_token_mdelem_storage;
@@ -287,8 +309,8 @@ typedef struct glb_lb_policy {
   grpc_client_channel_factory *cc_factory;
   grpc_channel_args *args;
 
-  /** deadline for the LB's call */
-  gpr_timespec deadline;
+  /** timeout in milliseconds for the LB call. 0 means no deadline. */
+  int lb_call_timeout_ms;
 
   /** for communicating with the LB server */
   grpc_channel *lb_channel;
@@ -316,6 +338,10 @@ typedef struct glb_lb_policy {
   /************************************************************/
   /*  client data associated with the LB server communication */
   /************************************************************/
+
+  /* Finished sending initial request. */
+  grpc_closure lb_on_sent_initial_request;
+
   /* Status from the LB server has been received. This signals the end of the LB
    * call. */
   grpc_closure lb_on_server_status_received;
@@ -348,6 +374,23 @@ typedef struct glb_lb_policy {
 
   /** LB call retry timer */
   grpc_timer lb_call_retry_timer;
+
+  bool initial_request_sent;
+  bool seen_initial_response;
+
+  /* Stats for client-side load reporting. Should be unreffed and
+   * recreated whenever lb_call is replaced. */
+  grpc_grpclb_client_stats *client_stats;
+  /* Interval and timer for next client load report. */
+  gpr_timespec client_stats_report_interval;
+  grpc_timer client_load_report_timer;
+  bool client_load_report_timer_pending;
+  bool last_client_load_report_counters_were_zero;
+  /* Closure used for either the load report timer or the callback for
+   * completion of sending the load report. */
+  grpc_closure client_load_report_closure;
+  /* Client load report message payload. */
+  grpc_byte_buffer *client_load_report_payload;
 } glb_lb_policy;
 
 /* Keeps track and reacts to changes in connectivity of the RR instance */
@@ -531,7 +574,7 @@ static bool update_lb_connectivity_status_locked(
       GPR_ASSERT(new_rr_state_error == GRPC_ERROR_NONE);
   }
 
-  if (grpc_lb_glb_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
     gpr_log(GPR_INFO,
             "Setting grpclb's state to %s from new RR policy %p state.",
             grpc_connectivity_state_name(new_rr_state),
@@ -552,11 +595,11 @@ static bool pick_from_internal_rr_locked(
     grpc_connected_subchannel **target, wrapped_rr_closure_arg *wc_arg) {
   GPR_ASSERT(rr_policy != NULL);
   const bool pick_done = grpc_lb_policy_pick_locked(
-      exec_ctx, rr_policy, pick_args, target, (void **)&wc_arg->lb_token,
-      &wc_arg->wrapper_closure);
+      exec_ctx, rr_policy, pick_args, target, wc_arg->context,
+      (void **)&wc_arg->lb_token, &wc_arg->wrapper_closure);
   if (pick_done) {
     /* synchronous grpc_lb_policy_pick call. Unref the RR policy. */
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO, "Unreffing RR (0x%" PRIxPTR ")",
               (intptr_t)wc_arg->rr_policy);
     }
@@ -567,7 +610,12 @@ static bool pick_from_internal_rr_locked(
                                   pick_args->lb_token_mdelem_storage,
                                   GRPC_MDELEM_REF(wc_arg->lb_token));
 
-    gpr_free(wc_arg);
+    // Pass on client stats via context. Passes ownership of the reference.
+    GPR_ASSERT(wc_arg->client_stats != NULL);
+    wc_arg->context[GRPC_GRPCLB_CLIENT_STATS].value = wc_arg->client_stats;
+    wc_arg->context[GRPC_GRPCLB_CLIENT_STATS].destroy = destroy_client_stats;
+
+    gpr_free(wc_arg->free_when_done);
   }
   /* else, the pending pick will be registered and taken care of by the
    * pending pick list inside the RR policy (glb_policy->rr_policy).
@@ -637,7 +685,7 @@ static void rr_handover_locked(grpc_exec_ctx *exec_ctx,
   if (!replace_old_rr) {
     /* dispose of the new RR policy that won't be used after all */
     GRPC_LB_POLICY_UNREF(exec_ctx, new_rr_policy, "rr_handover_no_replace");
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO,
               "Keeping old RR policy (%p) despite new serverlist: new RR "
               "policy was in %s connectivity state.",
@@ -647,7 +695,7 @@ static void rr_handover_locked(grpc_exec_ctx *exec_ctx,
     return;
   }
 
-  if (grpc_lb_glb_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
     gpr_log(GPR_INFO, "Created RR policy (%p) to replace old RR (%p)",
             (void *)new_rr_policy, (void *)glb_policy->rr_policy);
   }
@@ -690,7 +738,9 @@ static void rr_handover_locked(grpc_exec_ctx *exec_ctx,
     glb_policy->pending_picks = pp->next;
     GRPC_LB_POLICY_REF(glb_policy->rr_policy, "rr_handover_pending_pick");
     pp->wrapped_on_complete_arg.rr_policy = glb_policy->rr_policy;
-    if (grpc_lb_glb_trace) {
+    pp->wrapped_on_complete_arg.client_stats =
+        grpc_grpclb_client_stats_ref(glb_policy->client_stats);
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO, "Pending pick about to PICK from 0x%" PRIxPTR "",
               (intptr_t)glb_policy->rr_policy);
     }
@@ -704,7 +754,7 @@ static void rr_handover_locked(grpc_exec_ctx *exec_ctx,
     glb_policy->pending_pings = pping->next;
     GRPC_LB_POLICY_REF(glb_policy->rr_policy, "rr_handover_pending_ping");
     pping->wrapped_notify_arg.rr_policy = glb_policy->rr_policy;
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO, "Pending ping about to PING from 0x%" PRIxPTR "",
               (intptr_t)glb_policy->rr_policy);
     }
@@ -857,16 +907,29 @@ static grpc_lb_policy *glb_create(grpc_exec_ctx *exec_ctx,
   GPR_ASSERT(uri->path[0] != '\0');
   glb_policy->server_name =
       gpr_strdup(uri->path[0] == '/' ? uri->path + 1 : uri->path);
-  if (grpc_lb_glb_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
     gpr_log(GPR_INFO, "Will use '%s' as the server name for LB request.",
             glb_policy->server_name);
   }
   grpc_uri_destroy(uri);
 
   glb_policy->cc_factory = args->client_channel_factory;
-  glb_policy->args = grpc_channel_args_copy(args->args);
   GPR_ASSERT(glb_policy->cc_factory != NULL);
 
+  arg = grpc_channel_args_find(args->args, GRPC_ARG_GRPCLB_CALL_TIMEOUT_MS);
+  glb_policy->lb_call_timeout_ms =
+      grpc_channel_arg_get_integer(arg, (grpc_integer_options){0, 0, INT_MAX});
+
+  // Make sure that GRPC_ARG_LB_POLICY_NAME is set in channel args,
+  // since we use this to trigger the client_load_reporting filter.
+  grpc_arg new_arg;
+  new_arg.key = GRPC_ARG_LB_POLICY_NAME;
+  new_arg.type = GRPC_ARG_STRING;
+  new_arg.value.string = "grpclb";
+  static const char *args_to_remove[] = {GRPC_ARG_LB_POLICY_NAME};
+  glb_policy->args = grpc_channel_args_copy_and_add_and_remove(
+      args->args, args_to_remove, GPR_ARRAY_SIZE(args_to_remove), &new_arg, 1);
+
   grpc_slice_hash_table *targets_info = NULL;
   /* Create a client channel over them to communicate with a LB service */
   char *lb_service_target_addresses =
@@ -880,6 +943,8 @@ static grpc_lb_policy *glb_create(grpc_exec_ctx *exec_ctx,
   grpc_channel_args_destroy(exec_ctx, lb_channel_args);
   gpr_free(lb_service_target_addresses);
   if (glb_policy->lb_channel == NULL) {
+    gpr_free((void *)glb_policy->server_name);
+    grpc_channel_args_destroy(exec_ctx, glb_policy->args);
     gpr_free(glb_policy);
     return NULL;
   }
@@ -895,6 +960,9 @@ static void glb_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   GPR_ASSERT(glb_policy->pending_pings == NULL);
   gpr_free((void *)glb_policy->server_name);
   grpc_channel_args_destroy(exec_ctx, glb_policy->args);
+  if (glb_policy->client_stats != NULL) {
+    grpc_grpclb_client_stats_unref(glb_policy->client_stats);
+  }
   grpc_channel_destroy(glb_policy->lb_channel);
   glb_policy->lb_channel = NULL;
   grpc_connectivity_state_destroy(exec_ctx, &glb_policy->state_tracker);
@@ -1011,7 +1079,8 @@ static void glb_exit_idle_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
 
 static int glb_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                            const grpc_lb_policy_pick_args *pick_args,
-                           grpc_connected_subchannel **target, void **user_data,
+                           grpc_connected_subchannel **target,
+                           grpc_call_context_element *context, void **user_data,
                            grpc_closure *on_complete) {
   if (pick_args->lb_token_mdelem_storage == NULL) {
     *target = NULL;
@@ -1023,11 +1092,10 @@ static int glb_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
   }
 
   glb_lb_policy *glb_policy = (glb_lb_policy *)pol;
-  glb_policy->deadline = pick_args->deadline;
   bool pick_done;
 
   if (glb_policy->rr_policy != NULL) {
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO, "grpclb %p about to PICK from RR %p",
               (void *)glb_policy, (void *)glb_policy->rr_policy);
     }
@@ -1039,6 +1107,10 @@ static int glb_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                       grpc_schedule_on_exec_ctx);
     wc_arg->rr_policy = glb_policy->rr_policy;
     wc_arg->target = target;
+    wc_arg->context = context;
+    GPR_ASSERT(glb_policy->client_stats != NULL);
+    wc_arg->client_stats =
+        grpc_grpclb_client_stats_ref(glb_policy->client_stats);
     wc_arg->wrapped_closure = on_complete;
     wc_arg->lb_token_mdelem_storage = pick_args->lb_token_mdelem_storage;
     wc_arg->initial_metadata = pick_args->initial_metadata;
@@ -1046,13 +1118,13 @@ static int glb_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
     pick_done = pick_from_internal_rr_locked(exec_ctx, glb_policy->rr_policy,
                                              pick_args, target, wc_arg);
   } else {
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_DEBUG,
               "No RR policy in grpclb instance %p. Adding to grpclb's pending "
               "picks",
               (void *)(glb_policy));
     }
-    add_pending_pick(&glb_policy->pending_picks, pick_args, target,
+    add_pending_pick(&glb_policy->pending_picks, pick_args, target, context,
                      on_complete);
 
     if (!glb_policy->started_picking) {
@@ -1093,6 +1165,104 @@ static void glb_notify_on_state_change_locked(grpc_exec_ctx *exec_ctx,
       exec_ctx, &glb_policy->state_tracker, current, notify);
 }
 
+static void send_client_load_report_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                           grpc_error *error);
+
+static void schedule_next_client_load_report(grpc_exec_ctx *exec_ctx,
+                                             glb_lb_policy *glb_policy) {
+  const gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
+  const gpr_timespec next_client_load_report_time =
+      gpr_time_add(now, glb_policy->client_stats_report_interval);
+  grpc_closure_init(&glb_policy->client_load_report_closure,
+                    send_client_load_report_locked, glb_policy,
+                    grpc_combiner_scheduler(glb_policy->base.combiner, false));
+  grpc_timer_init(exec_ctx, &glb_policy->client_load_report_timer,
+                  next_client_load_report_time,
+                  &glb_policy->client_load_report_closure, now);
+}
+
+static void client_load_report_done_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                           grpc_error *error) {
+  glb_lb_policy *glb_policy = arg;
+  grpc_byte_buffer_destroy(glb_policy->client_load_report_payload);
+  glb_policy->client_load_report_payload = NULL;
+  if (error != GRPC_ERROR_NONE || glb_policy->lb_call == NULL) {
+    glb_policy->client_load_report_timer_pending = false;
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &glb_policy->base,
+                              "client_load_report");
+    return;
+  }
+  schedule_next_client_load_report(exec_ctx, glb_policy);
+}
+
+static void do_send_client_load_report_locked(grpc_exec_ctx *exec_ctx,
+                                              glb_lb_policy *glb_policy) {
+  grpc_op op;
+  memset(&op, 0, sizeof(op));
+  op.op = GRPC_OP_SEND_MESSAGE;
+  op.data.send_message.send_message = glb_policy->client_load_report_payload;
+  grpc_closure_init(&glb_policy->client_load_report_closure,
+                    client_load_report_done_locked, glb_policy,
+                    grpc_combiner_scheduler(glb_policy->base.combiner, false));
+  grpc_call_error call_error = grpc_call_start_batch_and_execute(
+      exec_ctx, glb_policy->lb_call, &op, 1,
+      &glb_policy->client_load_report_closure);
+  GPR_ASSERT(GRPC_CALL_OK == call_error);
+}
+
+static bool load_report_counters_are_zero(grpc_grpclb_request *request) {
+  return request->client_stats.num_calls_started == 0 &&
+         request->client_stats.num_calls_finished == 0 &&
+         request->client_stats.num_calls_finished_with_drop_for_rate_limiting ==
+             0 &&
+         request->client_stats
+                 .num_calls_finished_with_drop_for_load_balancing == 0 &&
+         request->client_stats.num_calls_finished_with_client_failed_to_send ==
+             0 &&
+         request->client_stats.num_calls_finished_known_received == 0;
+}
+
+static void send_client_load_report_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                           grpc_error *error) {
+  glb_lb_policy *glb_policy = arg;
+  if (error == GRPC_ERROR_CANCELLED || glb_policy->lb_call == NULL) {
+    glb_policy->client_load_report_timer_pending = false;
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &glb_policy->base,
+                              "client_load_report");
+    return;
+  }
+  // Construct message payload.
+  GPR_ASSERT(glb_policy->client_load_report_payload == NULL);
+  grpc_grpclb_request *request =
+      grpc_grpclb_load_report_request_create(glb_policy->client_stats);
+  // Skip client load report if the counters were all zero in the last
+  // report and they are still zero in this one.
+  if (load_report_counters_are_zero(request)) {
+    if (glb_policy->last_client_load_report_counters_were_zero) {
+      grpc_grpclb_request_destroy(request);
+      schedule_next_client_load_report(exec_ctx, glb_policy);
+      return;
+    }
+    glb_policy->last_client_load_report_counters_were_zero = true;
+  } else {
+    glb_policy->last_client_load_report_counters_were_zero = false;
+  }
+  grpc_slice request_payload_slice = grpc_grpclb_request_encode(request);
+  glb_policy->client_load_report_payload =
+      grpc_raw_byte_buffer_create(&request_payload_slice, 1);
+  grpc_slice_unref_internal(exec_ctx, request_payload_slice);
+  grpc_grpclb_request_destroy(request);
+  // If we've already sent the initial request, then we can go ahead and
+  // sent the load report.  Otherwise, we need to wait until the initial
+  // request has been sent to send this
+  // (see lb_on_sent_initial_request_locked() below).
+  if (glb_policy->initial_request_sent) {
+    do_send_client_load_report_locked(exec_ctx, glb_policy);
+  }
+}
+
+static void lb_on_sent_initial_request_locked(grpc_exec_ctx *exec_ctx,
+                                              void *arg, grpc_error *error);
 static void lb_on_server_status_received_locked(grpc_exec_ctx *exec_ctx,
                                                 void *arg, grpc_error *error);
 static void lb_on_response_received_locked(grpc_exec_ctx *exec_ctx, void *arg,
@@ -1107,13 +1277,24 @@ static void lb_call_init_locked(grpc_exec_ctx *exec_ctx,
    * glb_policy->base.interested_parties, which is comprised of the polling
    * entities from \a client_channel. */
   grpc_slice host = grpc_slice_from_copied_string(glb_policy->server_name);
+  gpr_timespec deadline =
+      glb_policy->lb_call_timeout_ms == 0
+          ? gpr_inf_future(GPR_CLOCK_MONOTONIC)
+          : gpr_time_add(gpr_now(GPR_CLOCK_MONOTONIC),
+                         gpr_time_from_millis(glb_policy->lb_call_timeout_ms,
+                                              GPR_TIMESPAN));
   glb_policy->lb_call = grpc_channel_create_pollset_set_call(
       exec_ctx, glb_policy->lb_channel, NULL, GRPC_PROPAGATE_DEFAULTS,
       glb_policy->base.interested_parties,
       GRPC_MDSTR_SLASH_GRPC_DOT_LB_DOT_V1_DOT_LOADBALANCER_SLASH_BALANCELOAD,
-      &host, glb_policy->deadline, NULL);
+      &host, deadline, NULL);
   grpc_slice_unref_internal(exec_ctx, host);
 
+  if (glb_policy->client_stats != NULL) {
+    grpc_grpclb_client_stats_unref(glb_policy->client_stats);
+  }
+  glb_policy->client_stats = grpc_grpclb_client_stats_create();
+
   grpc_metadata_array_init(&glb_policy->lb_initial_metadata_recv);
   grpc_metadata_array_init(&glb_policy->lb_trailing_metadata_recv);
 
@@ -1125,6 +1306,9 @@ static void lb_call_init_locked(grpc_exec_ctx *exec_ctx,
   grpc_slice_unref_internal(exec_ctx, request_payload_slice);
   grpc_grpclb_request_destroy(request);
 
+  grpc_closure_init(&glb_policy->lb_on_sent_initial_request,
+                    lb_on_sent_initial_request_locked, glb_policy,
+                    grpc_combiner_scheduler(glb_policy->base.combiner, false));
   grpc_closure_init(&glb_policy->lb_on_server_status_received,
                     lb_on_server_status_received_locked, glb_policy,
                     grpc_combiner_scheduler(glb_policy->base.combiner, false));
@@ -1138,6 +1322,10 @@ static void lb_call_init_locked(grpc_exec_ctx *exec_ctx,
                    GRPC_GRPCLB_RECONNECT_JITTER,
                    GRPC_GRPCLB_MIN_CONNECT_TIMEOUT_SECONDS * 1000,
                    GRPC_GRPCLB_RECONNECT_MAX_BACKOFF_SECONDS * 1000);
+
+  glb_policy->initial_request_sent = false;
+  glb_policy->seen_initial_response = false;
+  glb_policy->last_client_load_report_counters_were_zero = false;
 }
 
 static void lb_call_destroy_locked(grpc_exec_ctx *exec_ctx,
@@ -1151,6 +1339,10 @@ static void lb_call_destroy_locked(grpc_exec_ctx *exec_ctx,
 
   grpc_byte_buffer_destroy(glb_policy->lb_request_payload);
   grpc_slice_unref_internal(exec_ctx, glb_policy->lb_call_status_details);
+
+  if (!glb_policy->client_load_report_timer_pending) {
+    grpc_timer_cancel(exec_ctx, &glb_policy->client_load_report_timer);
+  }
 }
 
 /*
@@ -1163,7 +1355,7 @@ static void query_for_backends_locked(grpc_exec_ctx *exec_ctx,
 
   lb_call_init_locked(exec_ctx, glb_policy);
 
-  if (grpc_lb_glb_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
     gpr_log(GPR_INFO, "Query for backends (grpclb: %p, lb_call: %p)",
             (void *)glb_policy, (void *)glb_policy->lb_call);
   }
@@ -1179,21 +1371,27 @@ static void query_for_backends_locked(grpc_exec_ctx *exec_ctx,
   op->flags = 0;
   op->reserved = NULL;
   op++;
-
   op->op = GRPC_OP_RECV_INITIAL_METADATA;
   op->data.recv_initial_metadata.recv_initial_metadata =
       &glb_policy->lb_initial_metadata_recv;
   op->flags = 0;
   op->reserved = NULL;
   op++;
-
   GPR_ASSERT(glb_policy->lb_request_payload != NULL);
   op->op = GRPC_OP_SEND_MESSAGE;
   op->data.send_message.send_message = glb_policy->lb_request_payload;
   op->flags = 0;
   op->reserved = NULL;
   op++;
+  /* take a weak ref (won't prevent calling of \a glb_shutdown if the strong ref
+   * count goes to zero) to be unref'd in lb_on_sent_initial_request_locked() */
+  GRPC_LB_POLICY_WEAK_REF(&glb_policy->base, "lb_on_server_status_received");
+  call_error = grpc_call_start_batch_and_execute(
+      exec_ctx, glb_policy->lb_call, ops, (size_t)(op - ops),
+      &glb_policy->lb_on_sent_initial_request);
+  GPR_ASSERT(GRPC_CALL_OK == call_error);
 
+  op = ops;
   op->op = GRPC_OP_RECV_STATUS_ON_CLIENT;
   op->data.recv_status_on_client.trailing_metadata =
       &glb_policy->lb_trailing_metadata_recv;
@@ -1225,6 +1423,19 @@ static void query_for_backends_locked(grpc_exec_ctx *exec_ctx,
   GPR_ASSERT(GRPC_CALL_OK == call_error);
 }
 
+static void lb_on_sent_initial_request_locked(grpc_exec_ctx *exec_ctx,
+                                              void *arg, grpc_error *error) {
+  glb_lb_policy *glb_policy = arg;
+  glb_policy->initial_request_sent = true;
+  // If we attempted to send a client load report before the initial
+  // request was sent, send the load report now.
+  if (glb_policy->client_load_report_payload != NULL) {
+    do_send_client_load_report_locked(exec_ctx, glb_policy);
+  }
+  GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &glb_policy->base,
+                            "lb_on_response_received_locked");
+}
+
 static void lb_on_response_received_locked(grpc_exec_ctx *exec_ctx, void *arg,
                                            grpc_error *error) {
   glb_lb_policy *glb_policy = arg;
@@ -1240,58 +1451,91 @@ static void lb_on_response_received_locked(grpc_exec_ctx *exec_ctx, void *arg,
     grpc_byte_buffer_reader_init(&bbr, glb_policy->lb_response_payload);
     grpc_slice response_slice = grpc_byte_buffer_reader_readall(&bbr);
     grpc_byte_buffer_destroy(glb_policy->lb_response_payload);
-    grpc_grpclb_serverlist *serverlist =
-        grpc_grpclb_response_parse_serverlist(response_slice);
-    if (serverlist != NULL) {
-      GPR_ASSERT(glb_policy->lb_call != NULL);
-      grpc_slice_unref_internal(exec_ctx, response_slice);
-      if (grpc_lb_glb_trace) {
-        gpr_log(GPR_INFO, "Serverlist with %lu servers received",
-                (unsigned long)serverlist->num_servers);
-        for (size_t i = 0; i < serverlist->num_servers; ++i) {
-          grpc_resolved_address addr;
-          parse_server(serverlist->servers[i], &addr);
-          char *ipport;
-          grpc_sockaddr_to_string(&ipport, &addr, false);
-          gpr_log(GPR_INFO, "Serverlist[%lu]: %s", (unsigned long)i, ipport);
-          gpr_free(ipport);
+
+    grpc_grpclb_initial_response *response = NULL;
+    if (!glb_policy->seen_initial_response &&
+        (response = grpc_grpclb_initial_response_parse(response_slice)) !=
+            NULL) {
+      if (response->has_client_stats_report_interval) {
+        glb_policy->client_stats_report_interval =
+            gpr_time_max(gpr_time_from_seconds(1, GPR_TIMESPAN),
+                         grpc_grpclb_duration_to_timespec(
+                             &response->client_stats_report_interval));
+        if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
+          gpr_log(GPR_INFO,
+                  "received initial LB response message; "
+                  "client load reporting interval = %" PRId64 ".%09d sec",
+                  glb_policy->client_stats_report_interval.tv_sec,
+                  glb_policy->client_stats_report_interval.tv_nsec);
         }
+        /* take a weak ref (won't prevent calling of \a glb_shutdown() if the
+         * strong ref count goes to zero) to be unref'd in
+         * send_client_load_report() */
+        glb_policy->client_load_report_timer_pending = true;
+        GRPC_LB_POLICY_WEAK_REF(&glb_policy->base, "client_load_report");
+        schedule_next_client_load_report(exec_ctx, glb_policy);
+      } else if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
+        gpr_log(GPR_INFO,
+                "received initial LB response message; "
+                "client load reporting NOT enabled");
       }
+      grpc_grpclb_initial_response_destroy(response);
+      glb_policy->seen_initial_response = true;
+    } else {
+      grpc_grpclb_serverlist *serverlist =
+          grpc_grpclb_response_parse_serverlist(response_slice);
+      if (serverlist != NULL) {
+        GPR_ASSERT(glb_policy->lb_call != NULL);
+        if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
+          gpr_log(GPR_INFO, "Serverlist with %lu servers received",
+                  (unsigned long)serverlist->num_servers);
+          for (size_t i = 0; i < serverlist->num_servers; ++i) {
+            grpc_resolved_address addr;
+            parse_server(serverlist->servers[i], &addr);
+            char *ipport;
+            grpc_sockaddr_to_string(&ipport, &addr, false);
+            gpr_log(GPR_INFO, "Serverlist[%lu]: %s", (unsigned long)i, ipport);
+            gpr_free(ipport);
+          }
+        }
 
-      /* update serverlist */
-      if (serverlist->num_servers > 0) {
-        if (grpc_grpclb_serverlist_equals(glb_policy->serverlist, serverlist)) {
-          if (grpc_lb_glb_trace) {
+        /* update serverlist */
+        if (serverlist->num_servers > 0) {
+          if (grpc_grpclb_serverlist_equals(glb_policy->serverlist,
+                                            serverlist)) {
+            if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
+              gpr_log(GPR_INFO,
+                      "Incoming server list identical to current, ignoring.");
+            }
+            grpc_grpclb_destroy_serverlist(serverlist);
+          } else { /* new serverlist */
+            if (glb_policy->serverlist != NULL) {
+              /* dispose of the old serverlist */
+              grpc_grpclb_destroy_serverlist(glb_policy->serverlist);
+            }
+            /* and update the copy in the glb_lb_policy instance. This
+             * serverlist instance will be destroyed either upon the next
+             * update or in glb_destroy() */
+            glb_policy->serverlist = serverlist;
+
+            rr_handover_locked(exec_ctx, glb_policy);
+          }
+        } else {
+          if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
             gpr_log(GPR_INFO,
-                    "Incoming server list identical to current, ignoring.");
+                    "Received empty server list. Picks will stay pending until "
+                    "a response with > 0 servers is received");
           }
           grpc_grpclb_destroy_serverlist(serverlist);
-        } else { /* new serverlist */
-          if (glb_policy->serverlist != NULL) {
-            /* dispose of the old serverlist */
-            grpc_grpclb_destroy_serverlist(glb_policy->serverlist);
-          }
-          /* and update the copy in the glb_lb_policy instance. This serverlist
-           * instance will be destroyed either upon the next update or in
-           * glb_destroy() */
-          glb_policy->serverlist = serverlist;
-
-          rr_handover_locked(exec_ctx, glb_policy);
         }
-      } else {
-        if (grpc_lb_glb_trace) {
-          gpr_log(GPR_INFO,
-                  "Received empty server list. Picks will stay pending until a "
-                  "response with > 0 servers is received");
-        }
-        grpc_grpclb_destroy_serverlist(glb_policy->serverlist);
+      } else { /* serverlist == NULL */
+        gpr_log(GPR_ERROR, "Invalid LB response received: '%s'. Ignoring.",
+                grpc_dump_slice(response_slice, GPR_DUMP_ASCII | GPR_DUMP_HEX));
       }
-    } else { /* serverlist == NULL */
-      gpr_log(GPR_ERROR, "Invalid LB response received: '%s'. Ignoring.",
-              grpc_dump_slice(response_slice, GPR_DUMP_ASCII | GPR_DUMP_HEX));
-      grpc_slice_unref_internal(exec_ctx, response_slice);
     }
 
+    grpc_slice_unref_internal(exec_ctx, response_slice);
+
     if (!glb_policy->shutting_down) {
       /* keep listening for serverlist updates */
       op->op = GRPC_OP_RECV_MESSAGE;
@@ -1319,7 +1563,7 @@ static void lb_call_on_retry_timer_locked(grpc_exec_ctx *exec_ctx, void *arg,
   glb_lb_policy *glb_policy = arg;
 
   if (!glb_policy->shutting_down) {
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO, "Restaring call to LB server (grpclb %p)",
               (void *)glb_policy);
     }
@@ -1336,7 +1580,7 @@ static void lb_on_server_status_received_locked(grpc_exec_ctx *exec_ctx,
 
   GPR_ASSERT(glb_policy->lb_call != NULL);
 
-  if (grpc_lb_glb_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
     char *status_details =
         grpc_slice_to_c_string(glb_policy->lb_call_status_details);
     gpr_log(GPR_DEBUG,
@@ -1355,7 +1599,7 @@ static void lb_on_server_status_received_locked(grpc_exec_ctx *exec_ctx,
     gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
     gpr_timespec next_try =
         gpr_backoff_step(&glb_policy->lb_call_backoff_state, now);
-    if (grpc_lb_glb_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_DEBUG, "Connection to LB server lost (grpclb: %p)...",
               (void *)glb_policy);
       gpr_timespec timeout = gpr_time_sub(next_try, now);
@@ -1403,9 +1647,29 @@ grpc_lb_policy_factory *grpc_glb_lb_factory_create() {
 }
 
 /* Plugin registration */
+
+// Only add client_load_reporting filter if the grpclb LB policy is used.
+static bool maybe_add_client_load_reporting_filter(
+    grpc_exec_ctx *exec_ctx, grpc_channel_stack_builder *builder, void *arg) {
+  const grpc_channel_args *args =
+      grpc_channel_stack_builder_get_channel_arguments(builder);
+  const grpc_arg *channel_arg =
+      grpc_channel_args_find(args, GRPC_ARG_LB_POLICY_NAME);
+  if (channel_arg != NULL && channel_arg->type == GRPC_ARG_STRING &&
+      strcmp(channel_arg->value.string, "grpclb") == 0) {
+    return grpc_channel_stack_builder_append_filter(
+        builder, (const grpc_channel_filter *)arg, NULL, NULL);
+  }
+  return true;
+}
+
 void grpc_lb_policy_grpclb_init() {
   grpc_register_lb_policy(grpc_glb_lb_factory_create());
   grpc_register_tracer("glb", &grpc_lb_glb_trace);
+  grpc_channel_init_register_stage(GRPC_CLIENT_SUBCHANNEL,
+                                   GRPC_CHANNEL_INIT_BUILTIN_PRIORITY,
+                                   maybe_add_client_load_reporting_filter,
+                                   (void *)&grpc_client_load_reporting_filter);
 }
 
 void grpc_lb_policy_grpclb_shutdown() {}
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.c b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.c
new file mode 100644
index 0000000000..444c03b9aa
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.c
@@ -0,0 +1,133 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h"
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/atm.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/lib/channel/channel_args.h"
+
+#define GRPC_ARG_GRPCLB_CLIENT_STATS "grpc.grpclb_client_stats"
+
+struct grpc_grpclb_client_stats {
+  gpr_refcount refs;
+  gpr_atm num_calls_started;
+  gpr_atm num_calls_finished;
+  gpr_atm num_calls_finished_with_drop_for_rate_limiting;
+  gpr_atm num_calls_finished_with_drop_for_load_balancing;
+  gpr_atm num_calls_finished_with_client_failed_to_send;
+  gpr_atm num_calls_finished_known_received;
+};
+
+grpc_grpclb_client_stats* grpc_grpclb_client_stats_create() {
+  grpc_grpclb_client_stats* client_stats = gpr_zalloc(sizeof(*client_stats));
+  gpr_ref_init(&client_stats->refs, 1);
+  return client_stats;
+}
+
+grpc_grpclb_client_stats* grpc_grpclb_client_stats_ref(
+    grpc_grpclb_client_stats* client_stats) {
+  gpr_ref(&client_stats->refs);
+  return client_stats;
+}
+
+void grpc_grpclb_client_stats_unref(grpc_grpclb_client_stats* client_stats) {
+  if (gpr_unref(&client_stats->refs)) {
+    gpr_free(client_stats);
+  }
+}
+
+void grpc_grpclb_client_stats_add_call_started(
+    grpc_grpclb_client_stats* client_stats) {
+  gpr_atm_full_fetch_add(&client_stats->num_calls_started, (gpr_atm)1);
+}
+
+void grpc_grpclb_client_stats_add_call_finished(
+    bool finished_with_drop_for_rate_limiting,
+    bool finished_with_drop_for_load_balancing,
+    bool finished_with_client_failed_to_send, bool finished_known_received,
+    grpc_grpclb_client_stats* client_stats) {
+  gpr_atm_full_fetch_add(&client_stats->num_calls_finished, (gpr_atm)1);
+  if (finished_with_drop_for_rate_limiting) {
+    gpr_atm_full_fetch_add(
+        &client_stats->num_calls_finished_with_drop_for_rate_limiting,
+        (gpr_atm)1);
+  }
+  if (finished_with_drop_for_load_balancing) {
+    gpr_atm_full_fetch_add(
+        &client_stats->num_calls_finished_with_drop_for_load_balancing,
+        (gpr_atm)1);
+  }
+  if (finished_with_client_failed_to_send) {
+    gpr_atm_full_fetch_add(
+        &client_stats->num_calls_finished_with_client_failed_to_send,
+        (gpr_atm)1);
+  }
+  if (finished_known_received) {
+    gpr_atm_full_fetch_add(&client_stats->num_calls_finished_known_received,
+                           (gpr_atm)1);
+  }
+}
+
+static void atomic_get_and_reset_counter(int64_t* value, gpr_atm* counter) {
+  *value = (int64_t)gpr_atm_acq_load(counter);
+  gpr_atm_full_fetch_add(counter, (gpr_atm)(-*value));
+}
+
+void grpc_grpclb_client_stats_get(
+    grpc_grpclb_client_stats* client_stats, int64_t* num_calls_started,
+    int64_t* num_calls_finished,
+    int64_t* num_calls_finished_with_drop_for_rate_limiting,
+    int64_t* num_calls_finished_with_drop_for_load_balancing,
+    int64_t* num_calls_finished_with_client_failed_to_send,
+    int64_t* num_calls_finished_known_received) {
+  atomic_get_and_reset_counter(num_calls_started,
+                               &client_stats->num_calls_started);
+  atomic_get_and_reset_counter(num_calls_finished,
+                               &client_stats->num_calls_finished);
+  atomic_get_and_reset_counter(
+      num_calls_finished_with_drop_for_rate_limiting,
+      &client_stats->num_calls_finished_with_drop_for_rate_limiting);
+  atomic_get_and_reset_counter(
+      num_calls_finished_with_drop_for_load_balancing,
+      &client_stats->num_calls_finished_with_drop_for_load_balancing);
+  atomic_get_and_reset_counter(
+      num_calls_finished_with_client_failed_to_send,
+      &client_stats->num_calls_finished_with_client_failed_to_send);
+  atomic_get_and_reset_counter(
+      num_calls_finished_known_received,
+      &client_stats->num_calls_finished_known_received);
+}
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h
new file mode 100644
index 0000000000..0af4a919f8
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h
@@ -0,0 +1,65 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_GRPCLB_GRPCLB_CLIENT_STATS_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_GRPCLB_GRPCLB_CLIENT_STATS_H
+
+#include <stdbool.h>
+
+#include <grpc/impl/codegen/grpc_types.h>
+
+typedef struct grpc_grpclb_client_stats grpc_grpclb_client_stats;
+
+grpc_grpclb_client_stats* grpc_grpclb_client_stats_create();
+grpc_grpclb_client_stats* grpc_grpclb_client_stats_ref(
+    grpc_grpclb_client_stats* client_stats);
+void grpc_grpclb_client_stats_unref(grpc_grpclb_client_stats* client_stats);
+
+void grpc_grpclb_client_stats_add_call_started(
+    grpc_grpclb_client_stats* client_stats);
+void grpc_grpclb_client_stats_add_call_finished(
+    bool finished_with_drop_for_rate_limiting,
+    bool finished_with_drop_for_load_balancing,
+    bool finished_with_client_failed_to_send, bool finished_known_received,
+    grpc_grpclb_client_stats* client_stats);
+
+void grpc_grpclb_client_stats_get(
+    grpc_grpclb_client_stats* client_stats, int64_t* num_calls_started,
+    int64_t* num_calls_finished,
+    int64_t* num_calls_finished_with_drop_for_rate_limiting,
+    int64_t* num_calls_finished_with_drop_for_load_balancing,
+    int64_t* num_calls_finished_with_client_failed_to_send,
+    int64_t* num_calls_finished_known_received);
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_GRPCLB_GRPCLB_CLIENT_STATS_H \
+          */
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.c b/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.c
index 87549b78f0..81b6932fae 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.c
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.c
@@ -80,15 +80,45 @@ static bool decode_serverlist(pb_istream_t *stream, const pb_field_t *field,
 
 grpc_grpclb_request *grpc_grpclb_request_create(const char *lb_service_name) {
   grpc_grpclb_request *req = gpr_malloc(sizeof(grpc_grpclb_request));
-
-  req->has_client_stats = 0; /* TODO(dgq): add support for stats once defined */
-  req->has_initial_request = 1;
-  req->initial_request.has_name = 1;
+  req->has_client_stats = false;
+  req->has_initial_request = true;
+  req->initial_request.has_name = true;
   strncpy(req->initial_request.name, lb_service_name,
           GRPC_GRPCLB_SERVICE_NAME_MAX_LENGTH);
   return req;
 }
 
+static void populate_timestamp(gpr_timespec timestamp,
+                               struct _grpc_lb_v1_Timestamp *timestamp_pb) {
+  timestamp_pb->has_seconds = true;
+  timestamp_pb->seconds = timestamp.tv_sec;
+  timestamp_pb->has_nanos = true;
+  timestamp_pb->nanos = timestamp.tv_nsec;
+}
+
+grpc_grpclb_request *grpc_grpclb_load_report_request_create(
+    grpc_grpclb_client_stats *client_stats) {
+  grpc_grpclb_request *req = gpr_zalloc(sizeof(grpc_grpclb_request));
+  req->has_client_stats = true;
+  req->client_stats.has_timestamp = true;
+  populate_timestamp(gpr_now(GPR_CLOCK_REALTIME), &req->client_stats.timestamp);
+  req->client_stats.has_num_calls_started = true;
+  req->client_stats.has_num_calls_finished = true;
+  req->client_stats.has_num_calls_finished_with_drop_for_rate_limiting = true;
+  req->client_stats.has_num_calls_finished_with_drop_for_load_balancing = true;
+  req->client_stats.has_num_calls_finished_with_client_failed_to_send = true;
+  req->client_stats.has_num_calls_finished_with_client_failed_to_send = true;
+  req->client_stats.has_num_calls_finished_known_received = true;
+  grpc_grpclb_client_stats_get(
+      client_stats, &req->client_stats.num_calls_started,
+      &req->client_stats.num_calls_finished,
+      &req->client_stats.num_calls_finished_with_drop_for_rate_limiting,
+      &req->client_stats.num_calls_finished_with_drop_for_load_balancing,
+      &req->client_stats.num_calls_finished_with_client_failed_to_send,
+      &req->client_stats.num_calls_finished_known_received);
+  return req;
+}
+
 grpc_slice grpc_grpclb_request_encode(const grpc_grpclb_request *request) {
   size_t encoded_length;
   pb_ostream_t sizestream;
@@ -122,6 +152,9 @@ grpc_grpclb_initial_response *grpc_grpclb_initial_response_parse(
     gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
     return NULL;
   }
+
+  if (!res.has_initial_response) return NULL;
+
   grpc_grpclb_initial_response *initial_res =
       gpr_malloc(sizeof(grpc_grpclb_initial_response));
   memcpy(initial_res, &res.initial_response,
@@ -243,6 +276,15 @@ int grpc_grpclb_duration_compare(const grpc_grpclb_duration *lhs,
   return 0;
 }
 
+gpr_timespec grpc_grpclb_duration_to_timespec(
+    grpc_grpclb_duration *duration_pb) {
+  gpr_timespec duration;
+  duration.tv_sec = duration_pb->has_seconds ? duration_pb->seconds : 0;
+  duration.tv_nsec = duration_pb->has_nanos ? duration_pb->nanos : 0;
+  duration.clock_type = GPR_TIMESPAN;
+  return duration;
+}
+
 void grpc_grpclb_initial_response_destroy(
     grpc_grpclb_initial_response *response) {
   gpr_free(response);
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.h b/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.h
index d014b8800c..06873821bd 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.h
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.h
@@ -36,6 +36,7 @@
 
 #include <grpc/slice_buffer.h>
 
+#include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h"
 #include "src/core/ext/filters/client_channel/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.h"
 #include "src/core/ext/filters/client_channel/lb_policy_factory.h"
 
@@ -58,6 +59,8 @@ typedef struct grpc_grpclb_serverlist {
 
 /** Create a request for a gRPC LB service under \a lb_service_name */
 grpc_grpclb_request *grpc_grpclb_request_create(const char *lb_service_name);
+grpc_grpclb_request *grpc_grpclb_load_report_request_create(
+    grpc_grpclb_client_stats *client_stats);
 
 /** Protocol Buffers v3-encode \a request */
 grpc_slice grpc_grpclb_request_encode(const grpc_grpclb_request *request);
@@ -93,6 +96,9 @@ void grpc_grpclb_destroy_serverlist(grpc_grpclb_serverlist *serverlist);
 int grpc_grpclb_duration_compare(const grpc_grpclb_duration *lhs,
                                  const grpc_grpclb_duration *rhs);
 
+gpr_timespec grpc_grpclb_duration_to_timespec(
+    grpc_grpclb_duration *duration_pb);
+
 /** Destroy \a initial_response */
 void grpc_grpclb_initial_response_destroy(
     grpc_grpclb_initial_response *response);
diff --git a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.c b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.c
index 2b77cd39b8..b1c5dfc61c 100644
--- a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.c
+++ b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.c
@@ -189,7 +189,8 @@ static void pf_exit_idle_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
 
 static int pf_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                           const grpc_lb_policy_pick_args *pick_args,
-                          grpc_connected_subchannel **target, void **user_data,
+                          grpc_connected_subchannel **target,
+                          grpc_call_context_element *context, void **user_data,
                           grpc_closure *on_complete) {
   pick_first_lb_policy *p = (pick_first_lb_policy *)pol;
   pending_pick *pp;
diff --git a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c
index ff41e61b3e..6e7f410635 100644
--- a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c
+++ b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c
@@ -74,7 +74,7 @@
 
 typedef struct round_robin_lb_policy round_robin_lb_policy;
 
-int grpc_lb_round_robin_trace = 0;
+grpc_tracer_flag grpc_lb_round_robin_trace = GRPC_TRACER_INITIALIZER(false);
 
 /** List of entities waiting for a pick.
  *
@@ -198,7 +198,7 @@ static void advance_last_picked_locked(round_robin_lb_policy *p) {
     GPR_ASSERT(p->ready_list_last_pick == &p->ready_list);
   }
 
-  if (grpc_lb_round_robin_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     gpr_log(GPR_DEBUG,
             "[READYLIST, RR: %p] ADVANCED LAST PICK. NOW AT NODE %p (SC %p, "
             "CSC %p)",
@@ -228,7 +228,7 @@ static ready_list *add_connected_sc_locked(round_robin_lb_policy *p,
     p->ready_list.prev->next = new_elem;
     p->ready_list.prev = new_elem;
   }
-  if (grpc_lb_round_robin_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     gpr_log(GPR_DEBUG, "[READYLIST] ADDING NODE %p (Conn. SC %p)",
             (void *)new_elem, (void *)sd->subchannel);
   }
@@ -256,7 +256,7 @@ static void remove_disconnected_sc_locked(round_robin_lb_policy *p,
     node->next->prev = node->prev;
   }
 
-  if (grpc_lb_round_robin_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     gpr_log(GPR_DEBUG, "[READYLIST] REMOVED NODE %p (SC %p)", (void *)node,
             (void *)node->subchannel);
   }
@@ -276,7 +276,7 @@ static void rr_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   ready_list *elem;
 
-  if (grpc_lb_round_robin_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     gpr_log(GPR_DEBUG, "Destroying Round Robin policy at %p", (void *)pol);
   }
 
@@ -312,7 +312,7 @@ static void rr_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   pending_pick *pp;
   size_t i;
 
-  if (grpc_lb_round_robin_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     gpr_log(GPR_DEBUG, "Shutting down Round Robin policy at %p", (void *)pol);
   }
 
@@ -414,13 +414,14 @@ static void rr_exit_idle_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
 
 static int rr_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                           const grpc_lb_policy_pick_args *pick_args,
-                          grpc_connected_subchannel **target, void **user_data,
+                          grpc_connected_subchannel **target,
+                          grpc_call_context_element *context, void **user_data,
                           grpc_closure *on_complete) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   pending_pick *pp;
   ready_list *selected;
 
-  if (grpc_lb_round_robin_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     gpr_log(GPR_INFO, "Round Robin %p trying to pick", (void *)pol);
   }
 
@@ -433,7 +434,7 @@ static int rr_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
     if (user_data != NULL) {
       *user_data = selected->user_data;
     }
-    if (grpc_lb_round_robin_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
       gpr_log(GPR_DEBUG,
               "[RR PICK] TARGET <-- CONNECTED SUBCHANNEL %p (NODE %p)",
               (void *)*target, (void *)selected);
@@ -565,7 +566,7 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
         if (pp->user_data != NULL) {
           *pp->user_data = selected->user_data;
         }
-        if (grpc_lb_round_robin_trace) {
+        if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
           gpr_log(GPR_DEBUG,
                   "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (NODE %p)",
                   (void *)selected->subchannel, (void *)selected);
@@ -723,7 +724,7 @@ static grpc_lb_policy *round_robin_create(grpc_exec_ctx *exec_ctx,
     sc_args.args = new_args;
     grpc_subchannel *subchannel = grpc_client_channel_factory_create_subchannel(
         exec_ctx, args->client_channel_factory, &sc_args);
-    if (grpc_lb_round_robin_trace) {
+    if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
       char *address_uri =
           grpc_sockaddr_to_uri(&addresses->addresses[i].address);
       gpr_log(GPR_DEBUG, "Created subchannel %p for address uri %s",
@@ -767,7 +768,7 @@ static grpc_lb_policy *round_robin_create(grpc_exec_ctx *exec_ctx,
   grpc_connectivity_state_init(&p->state_tracker, GRPC_CHANNEL_IDLE,
                                "round_robin");
 
-  if (grpc_lb_round_robin_trace) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     gpr_log(GPR_DEBUG, "Created RR policy at %p with %lu subchannels",
             (void *)p, (unsigned long)p->num_subchannels);
   }
diff --git a/src/core/ext/filters/client_channel/subchannel.c b/src/core/ext/filters/client_channel/subchannel.c
index b2de85c4a1..1af3393a62 100644
--- a/src/core/ext/filters/client_channel/subchannel.c
+++ b/src/core/ext/filters/client_channel/subchannel.c
@@ -781,7 +781,7 @@ grpc_error *grpc_connected_subchannel_create_call(
   (*call)->connection = GRPC_CONNECTED_SUBCHANNEL_REF(con, "subchannel_call");
   const grpc_call_element_args call_args = {.call_stack = callstk,
                                             .server_transport_data = NULL,
-                                            .context = NULL,
+                                            .context = args->context,
                                             .path = args->path,
                                             .start_time = args->start_time,
                                             .deadline = args->deadline,
diff --git a/src/core/ext/filters/client_channel/subchannel.h b/src/core/ext/filters/client_channel/subchannel.h
index 6473de49b0..e433c33e40 100644
--- a/src/core/ext/filters/client_channel/subchannel.h
+++ b/src/core/ext/filters/client_channel/subchannel.h
@@ -119,6 +119,7 @@ typedef struct {
   gpr_timespec start_time;
   gpr_timespec deadline;
   gpr_arena *arena;
+  grpc_call_context_element *context;
 } grpc_connected_subchannel_call_args;
 
 grpc_error *grpc_connected_subchannel_create_call(
diff --git a/src/core/ext/filters/http/http_filters_plugin.c b/src/core/ext/filters/http/http_filters_plugin.c
index 195a1a8119..856a7dbd91 100644
--- a/src/core/ext/filters/http/http_filters_plugin.c
+++ b/src/core/ext/filters/http/http_filters_plugin.c
@@ -37,6 +37,7 @@
 #include "src/core/ext/filters/http/message_compress/message_compress_filter.h"
 #include "src/core/ext/filters/http/server/http_server_filter.h"
 #include "src/core/lib/channel/channel_stack_builder.h"
+#include "src/core/lib/surface/call.h"
 #include "src/core/lib/surface/channel_init.h"
 #include "src/core/lib/transport/transport_impl.h"
 
diff --git a/src/core/ext/filters/http/message_compress/message_compress_filter.c b/src/core/ext/filters/http/message_compress/message_compress_filter.c
index 1da8cf69cb..5a54a6ed15 100644
--- a/src/core/ext/filters/http/message_compress/message_compress_filter.c
+++ b/src/core/ext/filters/http/message_compress/message_compress_filter.c
@@ -47,6 +47,7 @@
 #include "src/core/lib/slice/slice_internal.h"
 #include "src/core/lib/slice/slice_string_helpers.h"
 #include "src/core/lib/support/string.h"
+#include "src/core/lib/surface/call.h"
 #include "src/core/lib/transport/static_metadata.h"
 
 #define INITIAL_METADATA_UNSEEN 0
@@ -197,7 +198,7 @@ static void finish_send_message(grpc_exec_ctx *exec_ctx,
   did_compress = grpc_msg_compress(exec_ctx, calld->compression_algorithm,
                                    &calld->slices, &tmp);
   if (did_compress) {
-    if (grpc_compression_trace) {
+    if (GRPC_TRACER_ON(grpc_compression_trace)) {
       char *algo_name;
       const size_t before_size = calld->slices.length;
       const size_t after_size = tmp.length;
@@ -211,7 +212,7 @@ static void finish_send_message(grpc_exec_ctx *exec_ctx,
     grpc_slice_buffer_swap(&calld->slices, &tmp);
     calld->send_flags |= GRPC_WRITE_INTERNAL_COMPRESS;
   } else {
-    if (grpc_compression_trace) {
+    if (GRPC_TRACER_ON(grpc_compression_trace)) {
       char *algo_name;
       GPR_ASSERT(grpc_compression_algorithm_name(calld->compression_algorithm,
                                                  &algo_name));
diff --git a/src/core/ext/filters/http/message_compress/message_compress_filter.h b/src/core/ext/filters/http/message_compress/message_compress_filter.h
index 75bfa17fba..135da4da62 100644
--- a/src/core/ext/filters/http/message_compress/message_compress_filter.h
+++ b/src/core/ext/filters/http/message_compress/message_compress_filter.h
@@ -38,8 +38,6 @@
 
 #include "src/core/lib/channel/channel_stack.h"
 
-extern int grpc_compression_trace;
-
 /** Compression filter for outgoing data.
  *
  * See <grpc/compression.h> for the available compression settings.
diff --git a/src/core/ext/filters/http/server/http_server_filter.c b/src/core/ext/filters/http/server/http_server_filter.c
index ff857878e4..9e495f4d42 100644
--- a/src/core/ext/filters/http/server/http_server_filter.c
+++ b/src/core/ext/filters/http/server/http_server_filter.c
@@ -46,8 +46,6 @@
 #define EXPECTED_CONTENT_TYPE "application/grpc"
 #define EXPECTED_CONTENT_TYPE_LENGTH sizeof(EXPECTED_CONTENT_TYPE) - 1
 
-extern int grpc_http_trace;
-
 typedef struct call_data {
   grpc_linked_mdelem status;
   grpc_linked_mdelem content_type;
diff --git a/src/core/ext/transport/chttp2/client/insecure/channel_create.c b/src/core/ext/transport/chttp2/client/insecure/channel_create.c
index 9c8505ddfa..ad674b8eb4 100644
--- a/src/core/ext/transport/chttp2/client/insecure/channel_create.c
+++ b/src/core/ext/transport/chttp2/client/insecure/channel_create.c
@@ -101,7 +101,7 @@ grpc_channel *grpc_insecure_channel_create(const char *target,
                                            void *reserved) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   GRPC_API_TRACE(
-      "grpc_insecure_channel_create(target=%p, args=%p, reserved=%p)", 3,
+      "grpc_insecure_channel_create(target=%s, args=%p, reserved=%p)", 3,
       (target, args, reserved));
   GPR_ASSERT(reserved == NULL);
   // Add channel arg containing the client channel factory.
diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.c b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
index d6b79bd492..fb8ceaecb0 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.c
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
@@ -89,8 +89,8 @@ static bool g_default_keepalive_permit_without_calls =
     DEFAULT_KEEPALIVE_PERMIT_WITHOUT_CALLS;
 
 #define MAX_CLIENT_STREAM_ID 0x7fffffffu
-int grpc_http_trace = 0;
-int grpc_flowctl_trace = 0;
+grpc_tracer_flag grpc_http_trace = GRPC_TRACER_INITIALIZER(false);
+grpc_tracer_flag grpc_flowctl_trace = GRPC_TRACER_INITIALIZER(false);
 
 static const grpc_transport_vtable vtable;
 
@@ -884,14 +884,23 @@ static void write_action_begin_locked(grpc_exec_ctx *exec_ctx, void *gt,
   GPR_TIMER_BEGIN("write_action_begin_locked", 0);
   grpc_chttp2_transport *t = gt;
   GPR_ASSERT(t->write_state != GRPC_CHTTP2_WRITE_STATE_IDLE);
-  if (!t->closed && grpc_chttp2_begin_write(exec_ctx, t)) {
-    set_write_state(exec_ctx, t, GRPC_CHTTP2_WRITE_STATE_WRITING,
-                    "begin writing");
-    grpc_closure_sched(exec_ctx, &t->write_action, GRPC_ERROR_NONE);
-  } else {
-    set_write_state(exec_ctx, t, GRPC_CHTTP2_WRITE_STATE_IDLE,
-                    "begin writing nothing");
-    GRPC_CHTTP2_UNREF_TRANSPORT(exec_ctx, t, "writing");
+  switch (t->closed ? GRPC_CHTTP2_NOTHING_TO_WRITE
+                    : grpc_chttp2_begin_write(exec_ctx, t)) {
+    case GRPC_CHTTP2_NOTHING_TO_WRITE:
+      set_write_state(exec_ctx, t, GRPC_CHTTP2_WRITE_STATE_IDLE,
+                      "begin writing nothing");
+      GRPC_CHTTP2_UNREF_TRANSPORT(exec_ctx, t, "writing");
+      break;
+    case GRPC_CHTTP2_PARTIAL_WRITE:
+      set_write_state(exec_ctx, t, GRPC_CHTTP2_WRITE_STATE_WRITING_WITH_MORE,
+                      "begin writing partial");
+      grpc_closure_sched(exec_ctx, &t->write_action, GRPC_ERROR_NONE);
+      break;
+    case GRPC_CHTTP2_FULL_WRITE:
+      set_write_state(exec_ctx, t, GRPC_CHTTP2_WRITE_STATE_WRITING,
+                      "begin writing");
+      grpc_closure_sched(exec_ctx, &t->write_action, GRPC_ERROR_NONE);
+      break;
   }
   GPR_TIMER_END("write_action_begin_locked", 0);
 }
@@ -988,7 +997,7 @@ void grpc_chttp2_add_incoming_goaway(grpc_exec_ctx *exec_ctx,
   t->seen_goaway = 1;
 
   /* When a client receives a GOAWAY with error code ENHANCE_YOUR_CALM and debug
-   * data equal to “too_many_pings”, it should log the occurrence at a log level
+   * data equal to "too_many_pings", it should log the occurrence at a log level
    * that is enabled by default and double the configured KEEPALIVE_TIME used
    * for new connections on that channel. */
   if (t->is_client && goaway_error == GRPC_HTTP2_ENHANCE_YOUR_CALM &&
@@ -1095,7 +1104,7 @@ void grpc_chttp2_complete_closure_step(grpc_exec_ctx *exec_ctx,
     return;
   }
   closure->next_data.scratch -= CLOSURE_BARRIER_FIRST_REF_BIT;
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     const char *errstr = grpc_error_string(error);
     gpr_log(GPR_DEBUG,
             "complete_closure_step: %p refs=%d flags=0x%04x desc=%s err=%s",
@@ -1240,7 +1249,7 @@ static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx, void *stream_op,
   grpc_transport_stream_op_batch_payload *op_payload = op->payload;
   grpc_chttp2_transport *t = s->t;
 
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     char *str = grpc_transport_stream_op_batch_string(op);
     gpr_log(GPR_DEBUG, "perform_stream_op_locked: %s; on_complete = %p", str,
             op->on_complete);
@@ -1483,9 +1492,9 @@ static void perform_stream_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
   grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
   grpc_chttp2_stream *s = (grpc_chttp2_stream *)gs;
 
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     char *str = grpc_transport_stream_op_batch_string(op);
-    gpr_log(GPR_DEBUG, "perform_stream_op[s=%p/%d]: %s", s, s->id, str);
+    gpr_log(GPR_DEBUG, "perform_stream_op[s=%p]: %s", s, str);
     gpr_free(str);
   }
 
@@ -2130,27 +2139,29 @@ static void end_all_the_calls(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
 
 static void update_bdp(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                        double bdp_dbl) {
-  uint32_t bdp;
-  if (bdp_dbl <= 0) {
-    bdp = 0;
-  } else if (bdp_dbl > UINT32_MAX) {
-    bdp = UINT32_MAX;
+  int32_t bdp;
+  const int32_t kMinBDP = 128;
+  if (bdp_dbl <= kMinBDP) {
+    bdp = kMinBDP;
+  } else if (bdp_dbl > INT32_MAX) {
+    bdp = INT32_MAX;
   } else {
-    bdp = (uint32_t)(bdp_dbl);
+    bdp = (int32_t)(bdp_dbl);
   }
   int64_t delta =
       (int64_t)bdp -
       (int64_t)t->settings[GRPC_LOCAL_SETTINGS]
                           [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
-  if (delta == 0 || (bdp != 0 && delta > -1024 && delta < 1024)) {
+  if (delta == 0 || (delta > -bdp / 10 && delta < bdp / 10)) {
     return;
   }
-  if (grpc_bdp_estimator_trace) {
+  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
     gpr_log(GPR_DEBUG, "%s: update initial window size to %d", t->peer_string,
             (int)bdp);
   }
-  push_setting(exec_ctx, t, GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE, bdp);
-  push_setting(exec_ctx, t, GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE, bdp);
+  push_setting(exec_ctx, t, GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE,
+               (uint32_t)bdp);
+  push_setting(exec_ctx, t, GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE, (uint32_t)bdp);
 }
 
 static grpc_error *try_http_parsing(grpc_exec_ctx *exec_ctx,
@@ -2305,7 +2316,7 @@ static void read_action_locked(grpc_exec_ctx *exec_ctx, void *tp,
 static void start_bdp_ping_locked(grpc_exec_ctx *exec_ctx, void *tp,
                                   grpc_error *error) {
   grpc_chttp2_transport *t = tp;
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     gpr_log(GPR_DEBUG, "%s: Start BDP ping", t->peer_string);
   }
   /* Reset the keepalive ping timer */
@@ -2318,7 +2329,7 @@ static void start_bdp_ping_locked(grpc_exec_ctx *exec_ctx, void *tp,
 static void finish_bdp_ping_locked(grpc_exec_ctx *exec_ctx, void *tp,
                                    grpc_error *error) {
   grpc_chttp2_transport *t = tp;
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     gpr_log(GPR_DEBUG, "%s: Complete BDP ping", t->peer_string);
   }
   grpc_bdp_estimator_complete_ping(&t->bdp_estimator);
@@ -2779,7 +2790,7 @@ static void benign_reclaimer_locked(grpc_exec_ctx *exec_ctx, void *arg,
       grpc_chttp2_stream_map_size(&t->stream_map) == 0) {
     /* Channel with no active streams: send a goaway to try and make it
      * disconnect cleanly */
-    if (grpc_resource_quota_trace) {
+    if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
       gpr_log(GPR_DEBUG, "HTTP2: %s - send goaway to free memory",
               t->peer_string);
     }
@@ -2787,7 +2798,8 @@ static void benign_reclaimer_locked(grpc_exec_ctx *exec_ctx, void *arg,
                 grpc_error_set_int(
                     GRPC_ERROR_CREATE_FROM_STATIC_STRING("Buffers full"),
                     GRPC_ERROR_INT_HTTP2_ERROR, GRPC_HTTP2_ENHANCE_YOUR_CALM));
-  } else if (error == GRPC_ERROR_NONE && grpc_resource_quota_trace) {
+  } else if (error == GRPC_ERROR_NONE &&
+             GRPC_TRACER_ON(grpc_resource_quota_trace)) {
     gpr_log(GPR_DEBUG,
             "HTTP2: %s - skip benign reclamation, there are still %" PRIdPTR
             " streams",
@@ -2808,7 +2820,7 @@ static void destructive_reclaimer_locked(grpc_exec_ctx *exec_ctx, void *arg,
   t->destructive_reclaimer_registered = false;
   if (error == GRPC_ERROR_NONE && n > 0) {
     grpc_chttp2_stream *s = grpc_chttp2_stream_map_rand(&t->stream_map);
-    if (grpc_resource_quota_trace) {
+    if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
       gpr_log(GPR_DEBUG, "HTTP2: %s - abandon stream id %d", t->peer_string,
               s->id);
     }
diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.h b/src/core/ext/transport/chttp2/transport/chttp2_transport.h
index c372174f2d..83b17d1936 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.h
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.h
@@ -34,11 +34,12 @@
 #ifndef GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_CHTTP2_TRANSPORT_H
 #define GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_CHTTP2_TRANSPORT_H
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/endpoint.h"
 #include "src/core/lib/transport/transport.h"
 
-extern int grpc_http_trace;
-extern int grpc_flowctl_trace;
+extern grpc_tracer_flag grpc_http_trace;
+extern grpc_tracer_flag grpc_flowctl_trace;
 
 grpc_transport *grpc_create_chttp2_transport(
     grpc_exec_ctx *exec_ctx, const grpc_channel_args *channel_args,
diff --git a/src/core/ext/transport/chttp2/transport/frame_settings.c b/src/core/ext/transport/chttp2/transport/frame_settings.c
index e3cd70d3f3..dbaafb5929 100644
--- a/src/core/ext/transport/chttp2/transport/frame_settings.c
+++ b/src/core/ext/transport/chttp2/transport/frame_settings.c
@@ -218,18 +218,18 @@ grpc_error *grpc_chttp2_settings_parser_parse(grpc_exec_ctx *exec_ctx, void *p,
               parser->incoming_settings[id] != parser->value) {
             t->initial_window_update +=
                 (int64_t)parser->value - parser->incoming_settings[id];
-            if (grpc_http_trace) {
+            if (GRPC_TRACER_ON(grpc_http_trace)) {
               gpr_log(GPR_DEBUG, "adding %d for initial_window change",
                       (int)t->initial_window_update);
             }
           }
           parser->incoming_settings[id] = parser->value;
-          if (grpc_http_trace) {
+          if (GRPC_TRACER_ON(grpc_http_trace)) {
             gpr_log(GPR_DEBUG, "CHTTP2:%s:%s: got setting %s = %d",
                     t->is_client ? "CLI" : "SVR", t->peer_string, sp->name,
                     parser->value);
           }
-        } else if (grpc_http_trace) {
+        } else if (GRPC_TRACER_ON(grpc_http_trace)) {
           gpr_log(GPR_ERROR, "CHTTP2: Ignoring unknown setting %d (value %d)",
                   parser->id, parser->value);
         }
diff --git a/src/core/ext/transport/chttp2/transport/hpack_encoder.c b/src/core/ext/transport/chttp2/transport/hpack_encoder.c
index 8fdd4ee77c..126e012aac 100644
--- a/src/core/ext/transport/chttp2/transport/hpack_encoder.c
+++ b/src/core/ext/transport/chttp2/transport/hpack_encoder.c
@@ -69,7 +69,7 @@ static grpc_slice_refcount terminal_slice_refcount = {NULL, NULL};
 static const grpc_slice terminal_slice = {&terminal_slice_refcount,
                                           .data.refcounted = {0, 0}};
 
-extern int grpc_http_trace;
+extern grpc_tracer_flag grpc_http_trace;
 
 typedef struct {
   int is_first_frame;
@@ -425,7 +425,7 @@ static void hpack_enc(grpc_exec_ctx *exec_ctx, grpc_chttp2_hpack_compressor *c,
         "Reserved header (colon-prefixed) happening after regular ones.");
   }
 
-  if (grpc_http_trace && !GRPC_MDELEM_IS_INTERNED(elem)) {
+  if (GRPC_TRACER_ON(grpc_http_trace) && !GRPC_MDELEM_IS_INTERNED(elem)) {
     char *k = grpc_slice_to_c_string(GRPC_MDKEY(elem));
     char *v = grpc_slice_to_c_string(GRPC_MDVALUE(elem));
     gpr_log(
@@ -616,7 +616,7 @@ void grpc_chttp2_hpack_compressor_set_max_table_size(
     }
   }
   c->advertise_table_size_change = 1;
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     gpr_log(GPR_DEBUG, "set max table size from encoder to %d", max_table_size);
   }
 }
diff --git a/src/core/ext/transport/chttp2/transport/hpack_parser.c b/src/core/ext/transport/chttp2/transport/hpack_parser.c
index 1846a85fc6..bb98bc4a79 100644
--- a/src/core/ext/transport/chttp2/transport/hpack_parser.c
+++ b/src/core/ext/transport/chttp2/transport/hpack_parser.c
@@ -50,8 +50,6 @@
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/transport/http2_errors.h"
 
-extern int grpc_http_trace;
-
 typedef enum {
   NOT_BINARY,
   BINARY_BEGIN,
@@ -666,7 +664,7 @@ static const uint8_t inverse_base64[256] = {
 /* emission helpers */
 static grpc_error *on_hdr(grpc_exec_ctx *exec_ctx, grpc_chttp2_hpack_parser *p,
                           grpc_mdelem md, int add_to_table) {
-  if (grpc_http_trace && !GRPC_MDELEM_IS_INTERNED(md)) {
+  if (GRPC_TRACER_ON(grpc_http_trace) && !GRPC_MDELEM_IS_INTERNED(md)) {
     char *k = grpc_slice_to_c_string(GRPC_MDKEY(md));
     char *v = grpc_slice_to_c_string(GRPC_MDVALUE(md));
     gpr_log(
@@ -1052,7 +1050,7 @@ static grpc_error *parse_lithdr_nvridx_v(grpc_exec_ctx *exec_ctx,
 static grpc_error *finish_max_tbl_size(grpc_exec_ctx *exec_ctx,
                                        grpc_chttp2_hpack_parser *p,
                                        const uint8_t *cur, const uint8_t *end) {
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     gpr_log(GPR_INFO, "MAX TABLE SIZE: %d", p->index);
   }
   grpc_error *err =
diff --git a/src/core/ext/transport/chttp2/transport/hpack_table.c b/src/core/ext/transport/chttp2/transport/hpack_table.c
index 9dd41fdbe1..7aaff55339 100644
--- a/src/core/ext/transport/chttp2/transport/hpack_table.c
+++ b/src/core/ext/transport/chttp2/transport/hpack_table.c
@@ -40,9 +40,10 @@
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/support/murmur_hash.h"
 
-extern int grpc_http_trace;
+extern grpc_tracer_flag grpc_http_trace;
 
 static struct {
   const char *key;
@@ -260,7 +261,7 @@ void grpc_chttp2_hptbl_set_max_bytes(grpc_exec_ctx *exec_ctx,
   if (tbl->max_bytes == max_bytes) {
     return;
   }
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     gpr_log(GPR_DEBUG, "Update hpack parser max size to %d", max_bytes);
   }
   while (tbl->mem_used > max_bytes) {
@@ -284,7 +285,7 @@ grpc_error *grpc_chttp2_hptbl_set_current_table_size(grpc_exec_ctx *exec_ctx,
     gpr_free(msg);
     return err;
   }
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     gpr_log(GPR_DEBUG, "Update hpack parser table size to %d", bytes);
   }
   while (tbl->mem_used > bytes) {
diff --git a/src/core/ext/transport/chttp2/transport/internal.h b/src/core/ext/transport/chttp2/transport/internal.h
index 0aaa4aebe5..8d66e396ee 100644
--- a/src/core/ext/transport/chttp2/transport/internal.h
+++ b/src/core/ext/transport/chttp2/transport/internal.h
@@ -552,9 +552,14 @@ void grpc_chttp2_initiate_write(grpc_exec_ctx *exec_ctx,
                                 grpc_chttp2_transport *t,
                                 bool covered_by_poller, const char *reason);
 
-/** Someone is unlocking the transport mutex: check to see if writes
-    are required, and frame them if so */
-bool grpc_chttp2_begin_write(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t);
+typedef enum {
+  GRPC_CHTTP2_NOTHING_TO_WRITE,
+  GRPC_CHTTP2_PARTIAL_WRITE,
+  GRPC_CHTTP2_FULL_WRITE,
+} grpc_chttp2_begin_write_result;
+
+grpc_chttp2_begin_write_result grpc_chttp2_begin_write(
+    grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t);
 void grpc_chttp2_end_write(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                            grpc_error *error);
 
@@ -629,13 +634,13 @@ void grpc_chttp2_complete_closure_step(grpc_exec_ctx *exec_ctx,
 #define GRPC_CHTTP2_CLIENT_CONNECT_STRLEN \
   (sizeof(GRPC_CHTTP2_CLIENT_CONNECT_STRING) - 1)
 
-extern int grpc_http_trace;
-extern int grpc_flowctl_trace;
+extern grpc_tracer_flag grpc_http_trace;
+extern grpc_tracer_flag grpc_flowctl_trace;
 
-#define GRPC_CHTTP2_IF_TRACING(stmt) \
-  if (!(grpc_http_trace))            \
-    ;                                \
-  else                               \
+#define GRPC_CHTTP2_IF_TRACING(stmt)      \
+  if (!(GRPC_TRACER_ON(grpc_http_trace))) \
+    ;                                     \
+  else                                    \
   stmt
 
 typedef enum {
@@ -648,7 +653,7 @@ typedef enum {
                                      dst_var, src_context, src_var)           \
   do {                                                                        \
     assert(id1 == id2);                                                       \
-    if (grpc_flowctl_trace) {                                                 \
+    if (GRPC_TRACER_ON(grpc_flowctl_trace)) {                                 \
       grpc_chttp2_flowctl_trace(                                              \
           __FILE__, __LINE__, phase, GRPC_CHTTP2_FLOWCTL_MOVE, #dst_context,  \
           #dst_var, #src_context, #src_var, transport->is_client, id1,        \
@@ -671,7 +676,7 @@ typedef enum {
 #define GRPC_CHTTP2_FLOW_CREDIT_COMMON(phase, transport, id, dst_context,      \
                                        dst_var, amount)                        \
   do {                                                                         \
-    if (grpc_flowctl_trace) {                                                  \
+    if (GRPC_TRACER_ON(grpc_flowctl_trace)) {                                  \
       grpc_chttp2_flowctl_trace(__FILE__, __LINE__, phase,                     \
                                 GRPC_CHTTP2_FLOWCTL_CREDIT, #dst_context,      \
                                 #dst_var, NULL, #amount, transport->is_client, \
@@ -729,7 +734,7 @@ typedef enum {
 #define GRPC_CHTTP2_FLOW_DEBIT_COMMON(phase, transport, id, dst_context,       \
                                       dst_var, amount)                         \
   do {                                                                         \
-    if (grpc_flowctl_trace) {                                                  \
+    if (GRPC_TRACER_ON(grpc_flowctl_trace)) {                                  \
       grpc_chttp2_flowctl_trace(__FILE__, __LINE__, phase,                     \
                                 GRPC_CHTTP2_FLOWCTL_DEBIT, #dst_context,       \
                                 #dst_var, NULL, #amount, transport->is_client, \
@@ -815,7 +820,7 @@ void grpc_chttp2_ack_ping(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
 /** Add a new ping strike to ping_recv_state.ping_strikes. If
     ping_recv_state.ping_strikes > ping_policy.max_ping_strikes, it sends GOAWAY
     with error code ENHANCE_YOUR_CALM and additional debug data resembling
-    “too_many_pings” followed by immediately closing the connection. */
+    "too_many_pings" followed by immediately closing the connection. */
 void grpc_chttp2_add_ping_strike(grpc_exec_ctx *exec_ctx,
                                  grpc_chttp2_transport *t);
 
diff --git a/src/core/ext/transport/chttp2/transport/parsing.c b/src/core/ext/transport/chttp2/transport/parsing.c
index 638b137316..1a676e2259 100644
--- a/src/core/ext/transport/chttp2/transport/parsing.c
+++ b/src/core/ext/transport/chttp2/transport/parsing.c
@@ -324,7 +324,7 @@ static grpc_error *init_frame_parser(grpc_exec_ctx *exec_ctx,
     case GRPC_CHTTP2_FRAME_GOAWAY:
       return init_goaway_parser(exec_ctx, t);
     default:
-      if (grpc_http_trace) {
+      if (GRPC_TRACER_ON(grpc_http_trace)) {
         gpr_log(GPR_ERROR, "Unknown frame type %02x", t->incoming_frame_type);
       }
       return init_skip_frame_parser(exec_ctx, t, 0);
@@ -418,11 +418,9 @@ static grpc_error *update_incoming_window(grpc_exec_ctx *exec_ctx,
 
     GRPC_CHTTP2_FLOW_DEBIT_STREAM_INCOMING_WINDOW_DELTA("parse", t, s,
                                                         incoming_frame_size);
-    if ((int64_t)t->settings[GRPC_SENT_SETTINGS]
-                            [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] +
-            (int64_t)s->incoming_window_delta - (int64_t)s->announce_window <=
-        (int64_t)t->settings[GRPC_SENT_SETTINGS]
-                            [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] /
+    if ((int64_t)s->incoming_window_delta - (int64_t)s->announce_window <=
+        -(int64_t)t->settings[GRPC_SENT_SETTINGS]
+                             [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] /
             2) {
       grpc_chttp2_become_writable(exec_ctx, t, s,
                                   GRPC_CHTTP2_STREAM_WRITE_INITIATE_UNCOVERED,
@@ -494,7 +492,7 @@ static void on_initial_header(grpc_exec_ctx *exec_ctx, void *tp,
 
   GPR_ASSERT(s != NULL);
 
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     char *key = grpc_slice_to_c_string(GRPC_MDKEY(md));
     char *value =
         grpc_dump_slice(GRPC_MDVALUE(md), GPR_DUMP_HEX | GPR_DUMP_ASCII);
@@ -574,7 +572,7 @@ static void on_trailing_header(grpc_exec_ctx *exec_ctx, void *tp,
 
   GPR_ASSERT(s != NULL);
 
-  if (grpc_http_trace) {
+  if (GRPC_TRACER_ON(grpc_http_trace)) {
     char *key = grpc_slice_to_c_string(GRPC_MDKEY(md));
     char *value =
         grpc_dump_slice(GRPC_MDVALUE(md), GPR_DUMP_HEX | GPR_DUMP_ASCII);
@@ -807,7 +805,7 @@ static grpc_error *parse_frame_slice(grpc_exec_ctx *exec_ctx,
   if (err == GRPC_ERROR_NONE) {
     return err;
   } else if (grpc_error_get_int(err, GRPC_ERROR_INT_STREAM_ID, NULL)) {
-    if (grpc_http_trace) {
+    if (GRPC_TRACER_ON(grpc_http_trace)) {
       const char *msg = grpc_error_string(err);
       gpr_log(GPR_ERROR, "%s", msg);
     }
diff --git a/src/core/ext/transport/chttp2/transport/writing.c b/src/core/ext/transport/chttp2/transport/writing.c
index 069780ae5a..5be1092946 100644
--- a/src/core/ext/transport/chttp2/transport/writing.c
+++ b/src/core/ext/transport/chttp2/transport/writing.c
@@ -74,7 +74,8 @@ static void maybe_initiate_ping(grpc_exec_ctx *exec_ctx,
   }
   if (!grpc_closure_list_empty(pq->lists[GRPC_CHTTP2_PCL_INFLIGHT])) {
     /* ping already in-flight: wait */
-    if (grpc_http_trace || grpc_bdp_estimator_trace) {
+    if (GRPC_TRACER_ON(grpc_http_trace) ||
+        GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
       gpr_log(GPR_DEBUG, "Ping delayed [%p]: already pinging", t->peer_string);
     }
     return;
@@ -82,7 +83,8 @@ static void maybe_initiate_ping(grpc_exec_ctx *exec_ctx,
   if (t->ping_state.pings_before_data_required == 0 &&
       t->ping_policy.max_pings_without_data != 0) {
     /* need to send something of substance before sending a ping again */
-    if (grpc_http_trace || grpc_bdp_estimator_trace) {
+    if (GRPC_TRACER_ON(grpc_http_trace) ||
+        GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
       gpr_log(GPR_DEBUG, "Ping delayed [%p]: too many recent pings: %d/%d",
               t->peer_string, t->ping_state.pings_before_data_required,
               t->ping_policy.max_pings_without_data);
@@ -96,7 +98,8 @@ static void maybe_initiate_ping(grpc_exec_ctx *exec_ctx,
           (int)t->ping_policy.min_time_between_pings.tv_nsec);*/
   if (gpr_time_cmp(elapsed, t->ping_policy.min_time_between_pings) < 0) {
     /* not enough elapsed time between successive pings */
-    if (grpc_http_trace || grpc_bdp_estimator_trace) {
+    if (GRPC_TRACER_ON(grpc_http_trace) ||
+        GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
       gpr_log(GPR_DEBUG,
               "Ping delayed [%p]: not enough time elapsed since last ping",
               t->peer_string);
@@ -160,19 +163,22 @@ static bool stream_ref_if_not_destroyed(gpr_refcount *r) {
   return true;
 }
 
+/* How many bytes of incoming flow control would we like to advertise */
 uint32_t grpc_chttp2_target_incoming_window(grpc_chttp2_transport *t) {
-  return (uint32_t)GPR_MAX(
+  return (uint32_t)GPR_MIN(
       (int64_t)((1u << 31) - 1),
       t->stream_total_over_incoming_window +
-          (int64_t)GPR_MAX(
-              t->settings[GRPC_SENT_SETTINGS]
-                         [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] -
-                  t->stream_total_under_incoming_window,
-              0));
+          t->settings[GRPC_SENT_SETTINGS]
+                     [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]);
 }
 
-bool grpc_chttp2_begin_write(grpc_exec_ctx *exec_ctx,
-                             grpc_chttp2_transport *t) {
+/* How many bytes would we like to put on the wire during a single syscall */
+static uint32_t target_write_size(grpc_chttp2_transport *t) {
+  return 1024 * 1024;
+}
+
+grpc_chttp2_begin_write_result grpc_chttp2_begin_write(
+    grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t) {
   grpc_chttp2_stream *s;
 
   GPR_TIMER_BEGIN("grpc_chttp2_begin_write", 0);
@@ -206,9 +212,20 @@ bool grpc_chttp2_begin_write(grpc_exec_ctx *exec_ctx,
     }
   }
 
+  bool partial_write = false;
+
   /* for each grpc_chttp2_stream that's become writable, frame it's data
      (according to available window sizes) and add to the output buffer */
-  while (grpc_chttp2_list_pop_writable_stream(t, &s)) {
+  while (true) {
+    if (t->outbuf.length > target_write_size(t)) {
+      partial_write = true;
+      break;
+    }
+
+    if (!grpc_chttp2_list_pop_writable_stream(t, &s)) {
+      break;
+    }
+
     bool sent_initial_metadata = s->sent_initial_metadata;
     bool now_writing = false;
 
@@ -395,7 +412,9 @@ bool grpc_chttp2_begin_write(grpc_exec_ctx *exec_ctx,
 
   GPR_TIMER_END("grpc_chttp2_begin_write", 0);
 
-  return t->outbuf.count > 0;
+  return t->outbuf.count > 0 ? (partial_write ? GRPC_CHTTP2_PARTIAL_WRITE
+                                              : GRPC_CHTTP2_FULL_WRITE)
+                             : GRPC_CHTTP2_NOTHING_TO_WRITE;
 }
 
 void grpc_chttp2_end_write(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
diff --git a/src/core/ext/transport/cronet/transport/cronet_transport.c b/src/core/ext/transport/cronet/transport/cronet_transport.c
index d4e89d6a6c..67974b0b6a 100644
--- a/src/core/ext/transport/cronet/transport/cronet_transport.c
+++ b/src/core/ext/transport/cronet/transport/cronet_transport.c
@@ -886,6 +886,10 @@ static bool op_can_be_run(grpc_transport_stream_op_batch *curr_op,
                !stream_state->state_op_done[OP_RECV_MESSAGE]) {
       CRONET_LOG(GPR_DEBUG, "Because");
       result = false;
+    } else if (curr_op->cancel_stream &&
+               !stream_state->state_callback_received[OP_CANCELED]) {
+      CRONET_LOG(GPR_DEBUG, "Because");
+      result = false;
     } else if (curr_op->recv_trailing_metadata) {
       /* We aren't done with trailing metadata yet */
       if (!stream_state->state_op_done[OP_RECV_TRAILING_METADATA]) {
diff --git a/src/core/lib/channel/channel_stack.c b/src/core/lib/channel/channel_stack.c
index 94382980eb..7db54d1107 100644
--- a/src/core/lib/channel/channel_stack.c
+++ b/src/core/lib/channel/channel_stack.c
@@ -38,7 +38,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-int grpc_trace_channel = 0;
+grpc_tracer_flag grpc_trace_channel = GRPC_TRACER_INITIALIZER(false);
 
 /* Memory layouts.
 
diff --git a/src/core/lib/channel/channel_stack.h b/src/core/lib/channel/channel_stack.h
index fdbcbdb018..c26d61b2ef 100644
--- a/src/core/lib/channel/channel_stack.h
+++ b/src/core/lib/channel/channel_stack.h
@@ -307,10 +307,10 @@ void grpc_call_element_signal_error(grpc_exec_ctx *exec_ctx,
                                     grpc_call_element *cur_elem,
                                     grpc_error *error);
 
-extern int grpc_trace_channel;
+extern grpc_tracer_flag grpc_trace_channel;
 
 #define GRPC_CALL_LOG_OP(sev, elem, op) \
-  if (grpc_trace_channel) grpc_call_log_op(sev, elem, op)
+  if (GRPC_TRACER_ON(grpc_trace_channel)) grpc_call_log_op(sev, elem, op)
 
 #ifdef __cplusplus
 }
diff --git a/src/core/lib/channel/channel_stack_builder.c b/src/core/lib/channel/channel_stack_builder.c
index 88c02edb70..44b030e4d1 100644
--- a/src/core/lib/channel/channel_stack_builder.c
+++ b/src/core/lib/channel/channel_stack_builder.c
@@ -38,7 +38,8 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/string_util.h>
 
-int grpc_trace_channel_stack_builder = 0;
+grpc_tracer_flag grpc_trace_channel_stack_builder =
+    GRPC_TRACER_INITIALIZER(false);
 
 typedef struct filter_node {
   struct filter_node *next;
diff --git a/src/core/lib/channel/channel_stack_builder.h b/src/core/lib/channel/channel_stack_builder.h
index c78111b00d..8cb36eb117 100644
--- a/src/core/lib/channel/channel_stack_builder.h
+++ b/src/core/lib/channel/channel_stack_builder.h
@@ -165,7 +165,7 @@ grpc_error *grpc_channel_stack_builder_finish(
 void grpc_channel_stack_builder_destroy(grpc_exec_ctx *exec_ctx,
                                         grpc_channel_stack_builder *builder);
 
-extern int grpc_trace_channel_stack_builder;
+extern grpc_tracer_flag grpc_trace_channel_stack_builder;
 
 #ifdef __cplusplus
 }
diff --git a/src/core/lib/channel/context.h b/src/core/lib/channel/context.h
index 6c931ad28a..f0a21113c5 100644
--- a/src/core/lib/channel/context.h
+++ b/src/core/lib/channel/context.h
@@ -50,6 +50,9 @@ typedef enum {
   /// Reserved for traffic_class_context.
   GRPC_CONTEXT_TRAFFIC,
 
+  /// Value is a \a grpc_grpclb_client_stats.
+  GRPC_GRPCLB_CLIENT_STATS,
+
   GRPC_CONTEXT_COUNT
 } grpc_context_index;
 
diff --git a/src/core/lib/debug/trace.c b/src/core/lib/debug/trace.c
index c56046785b..4dfea44c57 100644
--- a/src/core/lib/debug/trace.c
+++ b/src/core/lib/debug/trace.c
@@ -35,24 +35,31 @@
 
 #include <string.h>
 
-#include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include "src/core/lib/support/env.h"
 
+int grpc_tracer_set_enabled(const char *name, int enabled);
+
 typedef struct tracer {
   const char *name;
-  int *flag;
+  grpc_tracer_flag *flag;
   struct tracer *next;
 } tracer;
 static tracer *tracers;
 
-void grpc_register_tracer(const char *name, int *flag) {
+#ifdef GRPC_THREADSAFE_TRACER
+#define TRACER_SET(flag, on) gpr_atm_no_barrier_store(&(flag).value, (on))
+#else
+#define TRACER_SET(flag, on) (flag).value = (on)
+#endif
+
+void grpc_register_tracer(const char *name, grpc_tracer_flag *flag) {
   tracer *t = gpr_malloc(sizeof(*t));
   t->name = name;
   t->flag = flag;
   t->next = tracers;
-  *flag = 0;
+  TRACER_SET(*flag, false);
   tracers = t;
 }
 
@@ -121,13 +128,13 @@ int grpc_tracer_set_enabled(const char *name, int enabled) {
   tracer *t;
   if (0 == strcmp(name, "all")) {
     for (t = tracers; t; t = t->next) {
-      *t->flag = enabled;
+      TRACER_SET(*t->flag, enabled);
     }
   } else {
     int found = 0;
     for (t = tracers; t; t = t->next) {
       if (0 == strcmp(name, t->name)) {
-        *t->flag = enabled;
+        TRACER_SET(*t->flag, enabled);
         found = 1;
       }
     }
diff --git a/src/core/lib/debug/trace.h b/src/core/lib/debug/trace.h
index 7afc38db7e..ba432574d0 100644
--- a/src/core/lib/debug/trace.h
+++ b/src/core/lib/debug/trace.h
@@ -34,9 +34,35 @@
 #ifndef GRPC_CORE_LIB_DEBUG_TRACE_H
 #define GRPC_CORE_LIB_DEBUG_TRACE_H
 
+#include <grpc/support/atm.h>
 #include <grpc/support/port_platform.h>
+#include <stdbool.h>
 
-void grpc_register_tracer(const char *name, int *flag);
+#if defined(__has_feature)
+#if __has_feature(thread_sanitizer)
+#define GRPC_THREADSAFE_TRACER
+#endif
+#endif
+
+typedef struct {
+#ifdef GRPC_THREADSAFE_TRACER
+  gpr_atm value;
+#else
+  bool value;
+#endif
+} grpc_tracer_flag;
+
+#ifdef GRPC_THREADSAFE_TRACER
+#define GRPC_TRACER_ON(flag) (gpr_atm_no_barrier_load(&(flag).value) != 0)
+#define GRPC_TRACER_INITIALIZER(on) \
+  { (gpr_atm)(on) }
+#else
+#define GRPC_TRACER_ON(flag) ((flag).value)
+#define GRPC_TRACER_INITIALIZER(on) \
+  { (on) }
+#endif
+
+void grpc_register_tracer(const char *name, grpc_tracer_flag *flag);
 void grpc_tracer_init(const char *env_var_name);
 void grpc_tracer_shutdown(void);
 
diff --git a/src/core/lib/http/httpcli.c b/src/core/lib/http/httpcli.c
index 453a64b049..0ac2c2ad52 100644
--- a/src/core/lib/http/httpcli.c
+++ b/src/core/lib/http/httpcli.c
@@ -105,7 +105,7 @@ static void finish(grpc_exec_ctx *exec_ctx, internal_request *req,
                    grpc_error *error) {
   grpc_polling_entity_del_from_pollset_set(exec_ctx, req->pollent,
                                            req->context->pollset_set);
-  grpc_closure_sched(exec_ctx, req->on_done, error);
+  grpc_closure_sched(exec_ctx, req->on_done, GRPC_ERROR_REF(error));
   grpc_http_parser_destroy(&req->parser);
   if (req->addresses != NULL) {
     grpc_resolved_addresses_destroy(req->addresses);
diff --git a/src/core/lib/http/parser.c b/src/core/lib/http/parser.c
index aac506b800..a4357978e4 100644
--- a/src/core/lib/http/parser.c
+++ b/src/core/lib/http/parser.c
@@ -40,7 +40,7 @@
 #include <grpc/support/log.h>
 #include <grpc/support/useful.h>
 
-int grpc_http1_trace = 0;
+grpc_tracer_flag grpc_http1_trace = GRPC_TRACER_INITIALIZER(false);
 
 static char *buf2str(void *buffer, size_t length) {
   char *out = gpr_malloc(length + 1);
@@ -308,7 +308,7 @@ static grpc_error *addbyte(grpc_http_parser *parser, uint8_t byte,
     case GRPC_HTTP_FIRST_LINE:
     case GRPC_HTTP_HEADERS:
       if (parser->cur_line_length >= GRPC_HTTP_PARSER_MAX_HEADER_LENGTH) {
-        if (grpc_http1_trace)
+        if (GRPC_TRACER_ON(grpc_http1_trace))
           gpr_log(GPR_ERROR, "HTTP header max line length (%d) exceeded",
                   GRPC_HTTP_PARSER_MAX_HEADER_LENGTH);
         return GRPC_ERROR_CREATE_FROM_STATIC_STRING(
diff --git a/src/core/lib/http/parser.h b/src/core/lib/http/parser.h
index a68011dd43..a155fecf11 100644
--- a/src/core/lib/http/parser.h
+++ b/src/core/lib/http/parser.h
@@ -36,6 +36,7 @@
 
 #include <grpc/slice.h>
 #include <grpc/support/port_platform.h>
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/error.h"
 
 /* Maximum length of a header string of the form 'Key: Value\r\n' */
@@ -121,6 +122,6 @@ grpc_error *grpc_http_parser_eof(grpc_http_parser *parser);
 void grpc_http_request_destroy(grpc_http_request *request);
 void grpc_http_response_destroy(grpc_http_response *response);
 
-extern int grpc_http1_trace;
+extern grpc_tracer_flag grpc_http1_trace;
 
 #endif /* GRPC_CORE_LIB_HTTP_PARSER_H */
diff --git a/src/core/lib/iomgr/combiner.c b/src/core/lib/iomgr/combiner.c
index 05cdbdad2b..863f22c614 100644
--- a/src/core/lib/iomgr/combiner.c
+++ b/src/core/lib/iomgr/combiner.c
@@ -42,13 +42,13 @@
 #include "src/core/lib/iomgr/workqueue.h"
 #include "src/core/lib/profiling/timers.h"
 
-int grpc_combiner_trace = 0;
+grpc_tracer_flag grpc_combiner_trace = GRPC_TRACER_INITIALIZER(false);
 
-#define GRPC_COMBINER_TRACE(fn) \
-  do {                          \
-    if (grpc_combiner_trace) {  \
-      fn;                       \
-    }                           \
+#define GRPC_COMBINER_TRACE(fn)                \
+  do {                                         \
+    if (GRPC_TRACER_ON(grpc_combiner_trace)) { \
+      fn;                                      \
+    }                                          \
   } while (0)
 
 #define STATE_UNORPHANED 1
diff --git a/src/core/lib/iomgr/combiner.h b/src/core/lib/iomgr/combiner.h
index 75dcb0b70a..6ab7a2b26b 100644
--- a/src/core/lib/iomgr/combiner.h
+++ b/src/core/lib/iomgr/combiner.h
@@ -37,6 +37,7 @@
 #include <stddef.h>
 
 #include <grpc/support/atm.h>
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 #include "src/core/lib/support/mpscq.h"
 
@@ -78,6 +79,6 @@ grpc_closure_scheduler *grpc_combiner_finally_scheduler(grpc_combiner *lock,
 
 bool grpc_combiner_continue_exec_ctx(grpc_exec_ctx *exec_ctx);
 
-extern int grpc_combiner_trace;
+extern grpc_tracer_flag grpc_combiner_trace;
 
 #endif /* GRPC_CORE_LIB_IOMGR_COMBINER_H */
diff --git a/src/core/lib/iomgr/ev_epoll1_linux.c b/src/core/lib/iomgr/ev_epoll1_linux.c
new file mode 100644
index 0000000000..ad69f808cd
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epoll1_linux.c
@@ -0,0 +1,984 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/port.h"
+
+/* This polling engine is only relevant on linux kernels supporting epoll() */
+#ifdef GRPC_LINUX_EPOLL
+
+#include "src/core/lib/iomgr/ev_epoll1_linux.h"
+
+#include <assert.h>
+#include <errno.h>
+#include <poll.h>
+#include <pthread.h>
+#include <string.h>
+#include <sys/epoll.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/cpu.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/tls.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/iomgr_internal.h"
+#include "src/core/lib/iomgr/lockfree_event.h"
+#include "src/core/lib/iomgr/wakeup_fd_posix.h"
+#include "src/core/lib/iomgr/workqueue.h"
+#include "src/core/lib/profiling/timers.h"
+#include "src/core/lib/support/block_annotate.h"
+
+static grpc_wakeup_fd global_wakeup_fd;
+static int g_epfd;
+
+/*******************************************************************************
+ * Fd Declarations
+ */
+
+struct grpc_fd {
+  int fd;
+
+  gpr_atm read_closure;
+  gpr_atm write_closure;
+
+  struct grpc_fd *freelist_next;
+
+  /* The pollset that last noticed that the fd is readable. The actual type
+   * stored in this is (grpc_pollset *) */
+  gpr_atm read_notifier_pollset;
+
+  grpc_iomgr_object iomgr_object;
+};
+
+static void fd_global_init(void);
+static void fd_global_shutdown(void);
+
+/*******************************************************************************
+ * Pollset Declarations
+ */
+
+typedef enum { UNKICKED, KICKED, DESIGNATED_POLLER } kick_state;
+
+struct grpc_pollset_worker {
+  kick_state kick_state;
+  bool initialized_cv;
+  grpc_pollset_worker *next;
+  grpc_pollset_worker *prev;
+  gpr_cv cv;
+  grpc_closure_list schedule_on_end_work;
+};
+
+#define MAX_NEIGHBOURHOODS 1024
+
+typedef struct pollset_neighbourhood {
+  gpr_mu mu;
+  grpc_pollset *active_root;
+  char pad[GPR_CACHELINE_SIZE];
+} pollset_neighbourhood;
+
+struct grpc_pollset {
+  gpr_mu mu;
+  pollset_neighbourhood *neighbourhood;
+  bool reassigning_neighbourhood;
+  grpc_pollset_worker *root_worker;
+  bool kicked_without_poller;
+  bool seen_inactive;
+  bool shutting_down;          /* Is the pollset shutting down ? */
+  bool finish_shutdown_called; /* Is the 'finish_shutdown_locked()' called ? */
+  grpc_closure *shutdown_closure; /* Called after after shutdown is complete */
+  int begin_refs;
+
+  grpc_pollset *next;
+  grpc_pollset *prev;
+};
+
+/*******************************************************************************
+ * Pollset-set Declarations
+ */
+
+struct grpc_pollset_set {};
+
+/*******************************************************************************
+ * Common helpers
+ */
+
+static bool append_error(grpc_error **composite, grpc_error *error,
+                         const char *desc) {
+  if (error == GRPC_ERROR_NONE) return true;
+  if (*composite == GRPC_ERROR_NONE) {
+    *composite = GRPC_ERROR_CREATE_FROM_COPIED_STRING(desc);
+  }
+  *composite = grpc_error_add_child(*composite, error);
+  return false;
+}
+
+/*******************************************************************************
+ * Fd Definitions
+ */
+
+/* We need to keep a freelist not because of any concerns of malloc performance
+ * but instead so that implementations with multiple threads in (for example)
+ * epoll_wait deal with the race between pollset removal and incoming poll
+ * notifications.
+ *
+ * The problem is that the poller ultimately holds a reference to this
+ * object, so it is very difficult to know when is safe to free it, at least
+ * without some expensive synchronization.
+ *
+ * If we keep the object freelisted, in the worst case losing this race just
+ * becomes a spurious read notification on a reused fd.
+ */
+
+/* The alarm system needs to be able to wakeup 'some poller' sometimes
+ * (specifically when a new alarm needs to be triggered earlier than the next
+ * alarm 'epoch'). This wakeup_fd gives us something to alert on when such a
+ * case occurs. */
+
+static grpc_fd *fd_freelist = NULL;
+static gpr_mu fd_freelist_mu;
+
+static void fd_global_init(void) { gpr_mu_init(&fd_freelist_mu); }
+
+static void fd_global_shutdown(void) {
+  gpr_mu_lock(&fd_freelist_mu);
+  gpr_mu_unlock(&fd_freelist_mu);
+  while (fd_freelist != NULL) {
+    grpc_fd *fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+    gpr_free(fd);
+  }
+  gpr_mu_destroy(&fd_freelist_mu);
+}
+
+static grpc_fd *fd_create(int fd, const char *name) {
+  grpc_fd *new_fd = NULL;
+
+  gpr_mu_lock(&fd_freelist_mu);
+  if (fd_freelist != NULL) {
+    new_fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+  }
+  gpr_mu_unlock(&fd_freelist_mu);
+
+  if (new_fd == NULL) {
+    new_fd = gpr_malloc(sizeof(grpc_fd));
+  }
+
+  new_fd->fd = fd;
+  grpc_lfev_init(&new_fd->read_closure);
+  grpc_lfev_init(&new_fd->write_closure);
+  gpr_atm_no_barrier_store(&new_fd->read_notifier_pollset, (gpr_atm)NULL);
+
+  new_fd->freelist_next = NULL;
+
+  char *fd_name;
+  gpr_asprintf(&fd_name, "%s fd=%d", name, fd);
+  grpc_iomgr_register_object(&new_fd->iomgr_object, fd_name);
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+  gpr_log(GPR_DEBUG, "FD %d %p create %s", fd, (void *)new_fd, fd_name);
+#endif
+  gpr_free(fd_name);
+
+  struct epoll_event ev = {.events = (uint32_t)(EPOLLIN | EPOLLOUT | EPOLLET),
+                           .data.ptr = new_fd};
+  if (epoll_ctl(g_epfd, EPOLL_CTL_ADD, fd, &ev) != 0) {
+    gpr_log(GPR_ERROR, "epoll_ctl failed: %s", strerror(errno));
+  }
+
+  return new_fd;
+}
+
+static int fd_wrapped_fd(grpc_fd *fd) { return fd->fd; }
+
+/* Might be called multiple times */
+static void fd_shutdown(grpc_exec_ctx *exec_ctx, grpc_fd *fd, grpc_error *why) {
+  if (grpc_lfev_set_shutdown(exec_ctx, &fd->read_closure,
+                             GRPC_ERROR_REF(why))) {
+    shutdown(fd->fd, SHUT_RDWR);
+    grpc_lfev_set_shutdown(exec_ctx, &fd->write_closure, GRPC_ERROR_REF(why));
+  }
+  GRPC_ERROR_UNREF(why);
+}
+
+static void fd_orphan(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                      grpc_closure *on_done, int *release_fd,
+                      const char *reason) {
+  grpc_error *error = GRPC_ERROR_NONE;
+
+  if (!grpc_lfev_is_shutdown(&fd->read_closure)) {
+    fd_shutdown(exec_ctx, fd, GRPC_ERROR_CREATE_FROM_COPIED_STRING(reason));
+  }
+
+  /* If release_fd is not NULL, we should be relinquishing control of the file
+     descriptor fd->fd (but we still own the grpc_fd structure). */
+  if (release_fd != NULL) {
+    *release_fd = fd->fd;
+  } else {
+    close(fd->fd);
+  }
+
+  grpc_closure_sched(exec_ctx, on_done, GRPC_ERROR_REF(error));
+
+  grpc_iomgr_unregister_object(&fd->iomgr_object);
+  grpc_lfev_destroy(&fd->read_closure);
+  grpc_lfev_destroy(&fd->write_closure);
+
+  gpr_mu_lock(&fd_freelist_mu);
+  fd->freelist_next = fd_freelist;
+  fd_freelist = fd;
+  gpr_mu_unlock(&fd_freelist_mu);
+}
+
+static grpc_pollset *fd_get_read_notifier_pollset(grpc_exec_ctx *exec_ctx,
+                                                  grpc_fd *fd) {
+  gpr_atm notifier = gpr_atm_acq_load(&fd->read_notifier_pollset);
+  return (grpc_pollset *)notifier;
+}
+
+static bool fd_is_shutdown(grpc_fd *fd) {
+  return grpc_lfev_is_shutdown(&fd->read_closure);
+}
+
+static void fd_notify_on_read(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                              grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->read_closure, closure);
+}
+
+static void fd_notify_on_write(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                               grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->write_closure, closure);
+}
+
+static grpc_workqueue *fd_get_workqueue(grpc_fd *fd) {
+  return (grpc_workqueue *)0xb0b51ed;
+}
+
+static void fd_become_readable(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                               grpc_pollset *notifier) {
+  grpc_lfev_set_ready(exec_ctx, &fd->read_closure);
+
+  /* Note, it is possible that fd_become_readable might be called twice with
+     different 'notifier's when an fd becomes readable and it is in two epoll
+     sets (This can happen briefly during polling island merges). In such cases
+     it does not really matter which notifer is set as the read_notifier_pollset
+     (They would both point to the same polling island anyway) */
+  /* Use release store to match with acquire load in fd_get_read_notifier */
+  gpr_atm_rel_store(&fd->read_notifier_pollset, (gpr_atm)notifier);
+}
+
+static void fd_become_writable(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
+  grpc_lfev_set_ready(exec_ctx, &fd->write_closure);
+}
+
+/*******************************************************************************
+ * Pollset Definitions
+ */
+
+GPR_TLS_DECL(g_current_thread_pollset);
+GPR_TLS_DECL(g_current_thread_worker);
+static gpr_atm g_active_poller;
+static pollset_neighbourhood *g_neighbourhoods;
+static size_t g_num_neighbourhoods;
+static gpr_mu g_wq_mu;
+static grpc_closure_list g_wq_items;
+
+/* Return true if first in list */
+static bool worker_insert(grpc_pollset *pollset, grpc_pollset_worker *worker) {
+  if (pollset->root_worker == NULL) {
+    pollset->root_worker = worker;
+    worker->next = worker->prev = worker;
+    return true;
+  } else {
+    worker->next = pollset->root_worker;
+    worker->prev = worker->next->prev;
+    worker->next->prev = worker;
+    worker->prev->next = worker;
+    return false;
+  }
+}
+
+/* Return true if last in list */
+typedef enum { EMPTIED, NEW_ROOT, REMOVED } worker_remove_result;
+
+static worker_remove_result worker_remove(grpc_pollset *pollset,
+                                          grpc_pollset_worker *worker) {
+  if (worker == pollset->root_worker) {
+    if (worker == worker->next) {
+      pollset->root_worker = NULL;
+      return EMPTIED;
+    } else {
+      pollset->root_worker = worker->next;
+      worker->prev->next = worker->next;
+      worker->next->prev = worker->prev;
+      return NEW_ROOT;
+    }
+  } else {
+    worker->prev->next = worker->next;
+    worker->next->prev = worker->prev;
+    return REMOVED;
+  }
+}
+
+static size_t choose_neighbourhood(void) {
+  return (size_t)gpr_cpu_current_cpu() % g_num_neighbourhoods;
+}
+
+static grpc_error *pollset_global_init(void) {
+  gpr_tls_init(&g_current_thread_pollset);
+  gpr_tls_init(&g_current_thread_worker);
+  gpr_atm_no_barrier_store(&g_active_poller, 0);
+  global_wakeup_fd.read_fd = -1;
+  grpc_error *err = grpc_wakeup_fd_init(&global_wakeup_fd);
+  gpr_mu_init(&g_wq_mu);
+  g_wq_items = (grpc_closure_list)GRPC_CLOSURE_LIST_INIT;
+  if (err != GRPC_ERROR_NONE) return err;
+  struct epoll_event ev = {.events = (uint32_t)(EPOLLIN | EPOLLET),
+                           .data.ptr = &global_wakeup_fd};
+  if (epoll_ctl(g_epfd, EPOLL_CTL_ADD, global_wakeup_fd.read_fd, &ev) != 0) {
+    return GRPC_OS_ERROR(errno, "epoll_ctl");
+  }
+  g_num_neighbourhoods = GPR_CLAMP(gpr_cpu_num_cores(), 1, MAX_NEIGHBOURHOODS);
+  g_neighbourhoods =
+      gpr_zalloc(sizeof(*g_neighbourhoods) * g_num_neighbourhoods);
+  for (size_t i = 0; i < g_num_neighbourhoods; i++) {
+    gpr_mu_init(&g_neighbourhoods[i].mu);
+  }
+  return GRPC_ERROR_NONE;
+}
+
+static void pollset_global_shutdown(void) {
+  gpr_tls_destroy(&g_current_thread_pollset);
+  gpr_tls_destroy(&g_current_thread_worker);
+  gpr_mu_destroy(&g_wq_mu);
+  if (global_wakeup_fd.read_fd != -1) grpc_wakeup_fd_destroy(&global_wakeup_fd);
+  for (size_t i = 0; i < g_num_neighbourhoods; i++) {
+    gpr_mu_destroy(&g_neighbourhoods[i].mu);
+  }
+  gpr_free(g_neighbourhoods);
+}
+
+static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
+  gpr_mu_init(&pollset->mu);
+  *mu = &pollset->mu;
+  pollset->neighbourhood = &g_neighbourhoods[choose_neighbourhood()];
+  pollset->seen_inactive = true;
+}
+
+static void pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
+  gpr_mu_lock(&pollset->mu);
+  if (!pollset->seen_inactive) {
+    pollset_neighbourhood *neighbourhood = pollset->neighbourhood;
+    gpr_mu_unlock(&pollset->mu);
+  retry_lock_neighbourhood:
+    gpr_mu_lock(&neighbourhood->mu);
+    gpr_mu_lock(&pollset->mu);
+    if (!pollset->seen_inactive) {
+      if (pollset->neighbourhood != neighbourhood) {
+        gpr_mu_unlock(&neighbourhood->mu);
+        neighbourhood = pollset->neighbourhood;
+        gpr_mu_unlock(&pollset->mu);
+        goto retry_lock_neighbourhood;
+      }
+      pollset->prev->next = pollset->next;
+      pollset->next->prev = pollset->prev;
+      if (pollset == pollset->neighbourhood->active_root) {
+        pollset->neighbourhood->active_root =
+            pollset->next == pollset ? NULL : pollset->next;
+      }
+    }
+    gpr_mu_unlock(&pollset->neighbourhood->mu);
+  }
+  gpr_mu_unlock(&pollset->mu);
+  gpr_mu_destroy(&pollset->mu);
+}
+
+static grpc_error *pollset_kick_all(grpc_pollset *pollset) {
+  grpc_error *error = GRPC_ERROR_NONE;
+  if (pollset->root_worker != NULL) {
+    grpc_pollset_worker *worker = pollset->root_worker;
+    do {
+      if (worker->initialized_cv) {
+        worker->kick_state = KICKED;
+        gpr_cv_signal(&worker->cv);
+      } else {
+        worker->kick_state = KICKED;
+        append_error(&error, grpc_wakeup_fd_wakeup(&global_wakeup_fd),
+                     "pollset_shutdown");
+      }
+
+      worker = worker->next;
+    } while (worker != pollset->root_worker);
+  }
+  return error;
+}
+
+static void pollset_maybe_finish_shutdown(grpc_exec_ctx *exec_ctx,
+                                          grpc_pollset *pollset) {
+  if (pollset->shutdown_closure != NULL && pollset->root_worker == NULL &&
+      pollset->begin_refs == 0) {
+    grpc_closure_sched(exec_ctx, pollset->shutdown_closure, GRPC_ERROR_NONE);
+    pollset->shutdown_closure = NULL;
+  }
+}
+
+static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                             grpc_closure *closure) {
+  GPR_ASSERT(pollset->shutdown_closure == NULL);
+  pollset->shutdown_closure = closure;
+  GRPC_LOG_IF_ERROR("pollset_shutdown", pollset_kick_all(pollset));
+  pollset_maybe_finish_shutdown(exec_ctx, pollset);
+}
+
+#define MAX_EPOLL_EVENTS 100
+
+static int poll_deadline_to_millis_timeout(gpr_timespec deadline,
+                                           gpr_timespec now) {
+  gpr_timespec timeout;
+  if (gpr_time_cmp(deadline, gpr_inf_future(deadline.clock_type)) == 0) {
+    return -1;
+  }
+
+  if (gpr_time_cmp(deadline, now) <= 0) {
+    return 0;
+  }
+
+  static const gpr_timespec round_up = {
+      .clock_type = GPR_TIMESPAN, .tv_sec = 0, .tv_nsec = GPR_NS_PER_MS - 1};
+  timeout = gpr_time_sub(deadline, now);
+  int millis = gpr_time_to_millis(gpr_time_add(timeout, round_up));
+  return millis >= 1 ? millis : 1;
+}
+
+static grpc_error *pollset_epoll(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                                 gpr_timespec now, gpr_timespec deadline) {
+  struct epoll_event events[MAX_EPOLL_EVENTS];
+  static const char *err_desc = "pollset_poll";
+
+  int timeout = poll_deadline_to_millis_timeout(deadline, now);
+
+  if (timeout != 0) {
+    GRPC_SCHEDULING_START_BLOCKING_REGION;
+  }
+  int r;
+  do {
+    r = epoll_wait(g_epfd, events, MAX_EPOLL_EVENTS, timeout);
+  } while (r < 0 && errno == EINTR);
+  if (timeout != 0) {
+    GRPC_SCHEDULING_END_BLOCKING_REGION;
+  }
+
+  if (r < 0) return GRPC_OS_ERROR(errno, "epoll_wait");
+
+  grpc_error *error = GRPC_ERROR_NONE;
+  for (int i = 0; i < r; i++) {
+    void *data_ptr = events[i].data.ptr;
+    if (data_ptr == &global_wakeup_fd) {
+      gpr_mu_lock(&g_wq_mu);
+      grpc_closure_list_move(&g_wq_items, &exec_ctx->closure_list);
+      gpr_mu_unlock(&g_wq_mu);
+      append_error(&error, grpc_wakeup_fd_consume_wakeup(&global_wakeup_fd),
+                   err_desc);
+    } else {
+      grpc_fd *fd = (grpc_fd *)(data_ptr);
+      bool cancel = (events[i].events & (EPOLLERR | EPOLLHUP)) != 0;
+      bool read_ev = (events[i].events & (EPOLLIN | EPOLLPRI)) != 0;
+      bool write_ev = (events[i].events & EPOLLOUT) != 0;
+      if (read_ev || cancel) {
+        fd_become_readable(exec_ctx, fd, pollset);
+      }
+      if (write_ev || cancel) {
+        fd_become_writable(exec_ctx, fd);
+      }
+    }
+  }
+
+  return error;
+}
+
+static bool begin_worker(grpc_pollset *pollset, grpc_pollset_worker *worker,
+                         grpc_pollset_worker **worker_hdl, gpr_timespec *now,
+                         gpr_timespec deadline) {
+  if (worker_hdl != NULL) *worker_hdl = worker;
+  worker->initialized_cv = false;
+  worker->kick_state = UNKICKED;
+  worker->schedule_on_end_work = (grpc_closure_list)GRPC_CLOSURE_LIST_INIT;
+  pollset->begin_refs++;
+
+  if (pollset->seen_inactive) {
+    // pollset has been observed to be inactive, we need to move back to the
+    // active list
+    bool is_reassigning = false;
+    if (!pollset->reassigning_neighbourhood) {
+      is_reassigning = true;
+      pollset->reassigning_neighbourhood = true;
+      pollset->neighbourhood = &g_neighbourhoods[choose_neighbourhood()];
+    }
+    pollset_neighbourhood *neighbourhood = pollset->neighbourhood;
+    gpr_mu_unlock(&pollset->mu);
+  // pollset unlocked: state may change (even worker->kick_state)
+  retry_lock_neighbourhood:
+    gpr_mu_lock(&neighbourhood->mu);
+    gpr_mu_lock(&pollset->mu);
+    if (pollset->seen_inactive) {
+      if (neighbourhood != pollset->neighbourhood) {
+        gpr_mu_unlock(&neighbourhood->mu);
+        neighbourhood = pollset->neighbourhood;
+        gpr_mu_unlock(&pollset->mu);
+        goto retry_lock_neighbourhood;
+      }
+      pollset->seen_inactive = false;
+      if (neighbourhood->active_root == NULL) {
+        neighbourhood->active_root = pollset->next = pollset->prev = pollset;
+        if (gpr_atm_no_barrier_cas(&g_active_poller, 0, (gpr_atm)worker)) {
+          worker->kick_state = DESIGNATED_POLLER;
+        }
+      } else {
+        pollset->next = neighbourhood->active_root;
+        pollset->prev = pollset->next->prev;
+        pollset->next->prev = pollset->prev->next = pollset;
+      }
+    }
+    if (is_reassigning) {
+      GPR_ASSERT(pollset->reassigning_neighbourhood);
+      pollset->reassigning_neighbourhood = false;
+    }
+    gpr_mu_unlock(&neighbourhood->mu);
+  }
+  worker_insert(pollset, worker);
+  pollset->begin_refs--;
+  if (worker->kick_state == UNKICKED) {
+    GPR_ASSERT(gpr_atm_no_barrier_load(&g_active_poller) != (gpr_atm)worker);
+    worker->initialized_cv = true;
+    gpr_cv_init(&worker->cv);
+    while (worker->kick_state == UNKICKED &&
+           pollset->shutdown_closure == NULL) {
+      if (gpr_cv_wait(&worker->cv, &pollset->mu, deadline) &&
+          worker->kick_state == UNKICKED) {
+        worker->kick_state = KICKED;
+      }
+    }
+    *now = gpr_now(now->clock_type);
+  }
+
+  return worker->kick_state == DESIGNATED_POLLER &&
+         pollset->shutdown_closure == NULL;
+}
+
+static bool check_neighbourhood_for_available_poller(
+    pollset_neighbourhood *neighbourhood) {
+  bool found_worker = false;
+  do {
+    grpc_pollset *inspect = neighbourhood->active_root;
+    if (inspect == NULL) {
+      break;
+    }
+    gpr_mu_lock(&inspect->mu);
+    GPR_ASSERT(!inspect->seen_inactive);
+    grpc_pollset_worker *inspect_worker = inspect->root_worker;
+    if (inspect_worker != NULL) {
+      do {
+        switch (inspect_worker->kick_state) {
+          case UNKICKED:
+            if (gpr_atm_no_barrier_cas(&g_active_poller, 0,
+                                       (gpr_atm)inspect_worker)) {
+              inspect_worker->kick_state = DESIGNATED_POLLER;
+              if (inspect_worker->initialized_cv) {
+                gpr_cv_signal(&inspect_worker->cv);
+              }
+            }
+            // even if we didn't win the cas, there's a worker, we can stop
+            found_worker = true;
+            break;
+          case KICKED:
+            break;
+          case DESIGNATED_POLLER:
+            found_worker = true;  // ok, so someone else found the worker, but
+                                  // we'll accept that
+            break;
+        }
+        inspect_worker = inspect_worker->next;
+      } while (inspect_worker != inspect->root_worker);
+    }
+    if (!found_worker) {
+      inspect->seen_inactive = true;
+      if (inspect == neighbourhood->active_root) {
+        neighbourhood->active_root =
+            inspect->next == inspect ? NULL : inspect->next;
+      }
+      inspect->next->prev = inspect->prev;
+      inspect->prev->next = inspect->next;
+      inspect->next = inspect->prev = NULL;
+    }
+    gpr_mu_unlock(&inspect->mu);
+  } while (!found_worker);
+  return found_worker;
+}
+
+static void end_worker(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                       grpc_pollset_worker *worker,
+                       grpc_pollset_worker **worker_hdl) {
+  if (worker_hdl != NULL) *worker_hdl = NULL;
+  worker->kick_state = KICKED;
+  grpc_closure_list_move(&worker->schedule_on_end_work,
+                         &exec_ctx->closure_list);
+  if (gpr_atm_no_barrier_load(&g_active_poller) == (gpr_atm)worker) {
+    if (worker->next != worker && worker->next->kick_state == UNKICKED) {
+      GPR_ASSERT(worker->next->initialized_cv);
+      gpr_atm_no_barrier_store(&g_active_poller, (gpr_atm)worker->next);
+      worker->next->kick_state = DESIGNATED_POLLER;
+      gpr_cv_signal(&worker->next->cv);
+      if (grpc_exec_ctx_has_work(exec_ctx)) {
+        gpr_mu_unlock(&pollset->mu);
+        grpc_exec_ctx_flush(exec_ctx);
+        gpr_mu_lock(&pollset->mu);
+      }
+    } else {
+      gpr_atm_no_barrier_store(&g_active_poller, 0);
+      gpr_mu_unlock(&pollset->mu);
+      size_t poller_neighbourhood_idx =
+          (size_t)(pollset->neighbourhood - g_neighbourhoods);
+      bool found_worker = false;
+      bool scan_state[MAX_NEIGHBOURHOODS];
+      for (size_t i = 0; !found_worker && i < g_num_neighbourhoods; i++) {
+        pollset_neighbourhood *neighbourhood =
+            &g_neighbourhoods[(poller_neighbourhood_idx + i) %
+                              g_num_neighbourhoods];
+        if (gpr_mu_trylock(&neighbourhood->mu)) {
+          found_worker =
+              check_neighbourhood_for_available_poller(neighbourhood);
+          gpr_mu_unlock(&neighbourhood->mu);
+          scan_state[i] = true;
+        } else {
+          scan_state[i] = false;
+        }
+      }
+      for (size_t i = 0; !found_worker && i < g_num_neighbourhoods; i++) {
+        if (scan_state[i]) continue;
+        pollset_neighbourhood *neighbourhood =
+            &g_neighbourhoods[(poller_neighbourhood_idx + i) %
+                              g_num_neighbourhoods];
+        gpr_mu_lock(&neighbourhood->mu);
+        found_worker = check_neighbourhood_for_available_poller(neighbourhood);
+        gpr_mu_unlock(&neighbourhood->mu);
+      }
+      grpc_exec_ctx_flush(exec_ctx);
+      gpr_mu_lock(&pollset->mu);
+    }
+  } else if (grpc_exec_ctx_has_work(exec_ctx)) {
+    gpr_mu_unlock(&pollset->mu);
+    grpc_exec_ctx_flush(exec_ctx);
+    gpr_mu_lock(&pollset->mu);
+  }
+  if (worker->initialized_cv) {
+    gpr_cv_destroy(&worker->cv);
+  }
+  if (EMPTIED == worker_remove(pollset, worker)) {
+    pollset_maybe_finish_shutdown(exec_ctx, pollset);
+  }
+  GPR_ASSERT(gpr_atm_no_barrier_load(&g_active_poller) != (gpr_atm)worker);
+}
+
+/* pollset->po.mu lock must be held by the caller before calling this.
+   The function pollset_work() may temporarily release the lock (pollset->po.mu)
+   during the course of its execution but it will always re-acquire the lock and
+   ensure that it is held by the time the function returns */
+static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                                grpc_pollset_worker **worker_hdl,
+                                gpr_timespec now, gpr_timespec deadline) {
+  grpc_pollset_worker worker;
+  grpc_error *error = GRPC_ERROR_NONE;
+  static const char *err_desc = "pollset_work";
+  if (pollset->kicked_without_poller) {
+    pollset->kicked_without_poller = false;
+    return GRPC_ERROR_NONE;
+  }
+  gpr_tls_set(&g_current_thread_pollset, (intptr_t)pollset);
+  if (begin_worker(pollset, &worker, worker_hdl, &now, deadline)) {
+    gpr_tls_set(&g_current_thread_worker, (intptr_t)&worker);
+    GPR_ASSERT(!pollset->shutdown_closure);
+    GPR_ASSERT(!pollset->seen_inactive);
+    gpr_mu_unlock(&pollset->mu);
+    append_error(&error, pollset_epoll(exec_ctx, pollset, now, deadline),
+                 err_desc);
+    gpr_mu_lock(&pollset->mu);
+    gpr_tls_set(&g_current_thread_worker, 0);
+  }
+  end_worker(exec_ctx, pollset, &worker, worker_hdl);
+  gpr_tls_set(&g_current_thread_pollset, 0);
+  return error;
+}
+
+static grpc_error *pollset_kick(grpc_pollset *pollset,
+                                grpc_pollset_worker *specific_worker) {
+  if (specific_worker == NULL) {
+    if (gpr_tls_get(&g_current_thread_pollset) != (intptr_t)pollset) {
+      grpc_pollset_worker *root_worker = pollset->root_worker;
+      if (root_worker == NULL) {
+        pollset->kicked_without_poller = true;
+        return GRPC_ERROR_NONE;
+      }
+      grpc_pollset_worker *next_worker = root_worker->next;
+      if (root_worker == next_worker &&
+          root_worker == (grpc_pollset_worker *)gpr_atm_no_barrier_load(
+                             &g_active_poller)) {
+        root_worker->kick_state = KICKED;
+        return grpc_wakeup_fd_wakeup(&global_wakeup_fd);
+      } else if (next_worker->kick_state == UNKICKED) {
+        GPR_ASSERT(next_worker->initialized_cv);
+        next_worker->kick_state = KICKED;
+        gpr_cv_signal(&next_worker->cv);
+        return GRPC_ERROR_NONE;
+      } else {
+        return GRPC_ERROR_NONE;
+      }
+    } else {
+      return GRPC_ERROR_NONE;
+    }
+  } else if (specific_worker->kick_state == KICKED) {
+    return GRPC_ERROR_NONE;
+  } else if (gpr_tls_get(&g_current_thread_worker) ==
+             (intptr_t)specific_worker) {
+    specific_worker->kick_state = KICKED;
+    return GRPC_ERROR_NONE;
+  } else if (specific_worker ==
+             (grpc_pollset_worker *)gpr_atm_no_barrier_load(&g_active_poller)) {
+    specific_worker->kick_state = KICKED;
+    return grpc_wakeup_fd_wakeup(&global_wakeup_fd);
+  } else if (specific_worker->initialized_cv) {
+    specific_worker->kick_state = KICKED;
+    gpr_cv_signal(&specific_worker->cv);
+    return GRPC_ERROR_NONE;
+  } else {
+    specific_worker->kick_state = KICKED;
+    return GRPC_ERROR_NONE;
+  }
+}
+
+static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                           grpc_fd *fd) {}
+
+/*******************************************************************************
+ * Workqueue Definitions
+ */
+
+#ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue,
+                                     const char *file, int line,
+                                     const char *reason) {
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
+                            const char *file, int line, const char *reason) {}
+#else
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue) {
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx,
+                            grpc_workqueue *workqueue) {}
+#endif
+
+static void wq_sched(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                     grpc_error *error) {
+  // find a neighbourhood to wakeup
+  bool scheduled = false;
+  size_t initial_neighbourhood = choose_neighbourhood();
+  for (size_t i = 0; !scheduled && i < g_num_neighbourhoods; i++) {
+    pollset_neighbourhood *neighbourhood =
+        &g_neighbourhoods[(initial_neighbourhood + i) % g_num_neighbourhoods];
+    if (gpr_mu_trylock(&neighbourhood->mu)) {
+      if (neighbourhood->active_root != NULL) {
+        grpc_pollset *inspect = neighbourhood->active_root;
+        do {
+          if (gpr_mu_trylock(&inspect->mu)) {
+            if (inspect->root_worker != NULL) {
+              grpc_pollset_worker *inspect_worker = inspect->root_worker;
+              do {
+                if (inspect_worker->kick_state == UNKICKED) {
+                  inspect_worker->kick_state = KICKED;
+                  grpc_closure_list_append(
+                      &inspect_worker->schedule_on_end_work, closure, error);
+                  if (inspect_worker->initialized_cv) {
+                    gpr_cv_signal(&inspect_worker->cv);
+                  }
+                  scheduled = true;
+                }
+                inspect_worker = inspect_worker->next;
+              } while (!scheduled && inspect_worker != inspect->root_worker);
+            }
+            gpr_mu_unlock(&inspect->mu);
+          }
+          inspect = inspect->next;
+        } while (!scheduled && inspect != neighbourhood->active_root);
+      }
+      gpr_mu_unlock(&neighbourhood->mu);
+    }
+  }
+  if (!scheduled) {
+    gpr_mu_lock(&g_wq_mu);
+    grpc_closure_list_append(&g_wq_items, closure, error);
+    gpr_mu_unlock(&g_wq_mu);
+    GRPC_LOG_IF_ERROR("workqueue_scheduler",
+                      grpc_wakeup_fd_wakeup(&global_wakeup_fd));
+  }
+}
+
+static const grpc_closure_scheduler_vtable
+    singleton_workqueue_scheduler_vtable = {wq_sched, wq_sched,
+                                            "epoll1_workqueue"};
+
+static grpc_closure_scheduler singleton_workqueue_scheduler = {
+    &singleton_workqueue_scheduler_vtable};
+
+static grpc_closure_scheduler *workqueue_scheduler(grpc_workqueue *workqueue) {
+  return &singleton_workqueue_scheduler;
+}
+
+/*******************************************************************************
+ * Pollset-set Definitions
+ */
+
+static grpc_pollset_set *pollset_set_create(void) {
+  return (grpc_pollset_set *)((intptr_t)0xdeafbeef);
+}
+
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pss) {}
+
+static void pollset_set_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {}
+
+static void pollset_set_del_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {}
+
+static void pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {}
+
+static void pollset_set_del_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {}
+
+static void pollset_set_add_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {}
+
+static void pollset_set_del_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {}
+
+/*******************************************************************************
+ * Event engine binding
+ */
+
+static void shutdown_engine(void) {
+  fd_global_shutdown();
+  pollset_global_shutdown();
+}
+
+static const grpc_event_engine_vtable vtable = {
+    .pollset_size = sizeof(grpc_pollset),
+
+    .fd_create = fd_create,
+    .fd_wrapped_fd = fd_wrapped_fd,
+    .fd_orphan = fd_orphan,
+    .fd_shutdown = fd_shutdown,
+    .fd_is_shutdown = fd_is_shutdown,
+    .fd_notify_on_read = fd_notify_on_read,
+    .fd_notify_on_write = fd_notify_on_write,
+    .fd_get_read_notifier_pollset = fd_get_read_notifier_pollset,
+    .fd_get_workqueue = fd_get_workqueue,
+
+    .pollset_init = pollset_init,
+    .pollset_shutdown = pollset_shutdown,
+    .pollset_destroy = pollset_destroy,
+    .pollset_work = pollset_work,
+    .pollset_kick = pollset_kick,
+    .pollset_add_fd = pollset_add_fd,
+
+    .pollset_set_create = pollset_set_create,
+    .pollset_set_destroy = pollset_set_destroy,
+    .pollset_set_add_pollset = pollset_set_add_pollset,
+    .pollset_set_del_pollset = pollset_set_del_pollset,
+    .pollset_set_add_pollset_set = pollset_set_add_pollset_set,
+    .pollset_set_del_pollset_set = pollset_set_del_pollset_set,
+    .pollset_set_add_fd = pollset_set_add_fd,
+    .pollset_set_del_fd = pollset_set_del_fd,
+
+    .workqueue_ref = workqueue_ref,
+    .workqueue_unref = workqueue_unref,
+    .workqueue_scheduler = workqueue_scheduler,
+
+    .shutdown_engine = shutdown_engine,
+};
+
+/* It is possible that GLIBC has epoll but the underlying kernel doesn't.
+ * Create a dummy epoll_fd to make sure epoll support is available */
+const grpc_event_engine_vtable *grpc_init_epoll1_linux(bool explicit_request) {
+  /* TODO(ctiller): temporary, until this stabilizes */
+  if (!explicit_request) return NULL;
+
+  if (!grpc_has_wakeup_fd()) {
+    return NULL;
+  }
+
+  g_epfd = epoll_create1(EPOLL_CLOEXEC);
+  if (g_epfd < 0) {
+    gpr_log(GPR_ERROR, "epoll unavailable");
+    return NULL;
+  }
+
+  fd_global_init();
+
+  if (!GRPC_LOG_IF_ERROR("pollset_global_init", pollset_global_init())) {
+    close(g_epfd);
+    fd_global_shutdown();
+    return NULL;
+  }
+
+  return &vtable;
+}
+
+#else /* defined(GRPC_LINUX_EPOLL) */
+#if defined(GRPC_POSIX_SOCKET)
+#include "src/core/lib/iomgr/ev_posix.h"
+/* If GRPC_LINUX_EPOLL is not defined, it means epoll is not available. Return
+ * NULL */
+const grpc_event_engine_vtable *grpc_init_epoll1_linux(bool explicit_request) {
+  return NULL;
+}
+#endif /* defined(GRPC_POSIX_SOCKET) */
+#endif /* !defined(GRPC_LINUX_EPOLL) */
diff --git a/src/core/lib/iomgr/ev_epoll1_linux.h b/src/core/lib/iomgr/ev_epoll1_linux.h
new file mode 100644
index 0000000000..bd52478a7c
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epoll1_linux.h
@@ -0,0 +1,44 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_EV_EPOLL1_LINUX_H
+#define GRPC_CORE_LIB_IOMGR_EV_EPOLL1_LINUX_H
+
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/port.h"
+
+// a polling engine that utilizes a singleton epoll set and turnstile polling
+
+const grpc_event_engine_vtable *grpc_init_epoll1_linux(bool explicit_request);
+
+#endif /* GRPC_CORE_LIB_IOMGR_EV_EPOLL1_LINUX_H */
diff --git a/src/core/lib/iomgr/ev_epoll_limited_pollers_linux.c b/src/core/lib/iomgr/ev_epoll_limited_pollers_linux.c
new file mode 100644
index 0000000000..d23bf6c06c
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epoll_limited_pollers_linux.c
@@ -0,0 +1,2146 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/port.h"
+
+/* This polling engine is only relevant on linux kernels supporting epoll() */
+#ifdef GRPC_LINUX_EPOLL
+
+#include "src/core/lib/iomgr/ev_epoll_limited_pollers_linux.h"
+
+#include <assert.h>
+#include <errno.h>
+#include <limits.h>
+#include <poll.h>
+#include <pthread.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/epoll.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/tls.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/lib/debug/trace.h"
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/iomgr_internal.h"
+#include "src/core/lib/iomgr/lockfree_event.h"
+#include "src/core/lib/iomgr/timer.h"
+#include "src/core/lib/iomgr/wakeup_fd_posix.h"
+#include "src/core/lib/iomgr/workqueue.h"
+#include "src/core/lib/profiling/timers.h"
+#include "src/core/lib/support/block_annotate.h"
+#include "src/core/lib/support/env.h"
+
+#define GRPC_POLLING_TRACE(fmt, ...)        \
+  if (GRPC_TRACER_ON(grpc_polling_trace)) { \
+    gpr_log(GPR_INFO, (fmt), __VA_ARGS__);  \
+  }
+
+#define GRPC_POLLSET_KICK_BROADCAST ((grpc_pollset_worker *)1)
+
+/* Uncomment the following to enable extra checks on poll_object operations */
+/* #define PO_DEBUG */
+
+/* The maximum number of polling threads per polling island. By default no
+   limit */
+static int g_max_pollers_per_pi = INT_MAX;
+
+static int grpc_wakeup_signal = -1;
+static bool is_grpc_wakeup_signal_initialized = false;
+
+/* Implements the function defined in grpc_posix.h. This function might be
+ * called before even calling grpc_init() to set either a different signal to
+ * use. If signum == -1, then the use of signals is disabled */
+static void grpc_use_signal(int signum) {
+  grpc_wakeup_signal = signum;
+  is_grpc_wakeup_signal_initialized = true;
+
+  if (grpc_wakeup_signal < 0) {
+    gpr_log(GPR_INFO,
+            "Use of signals is disabled. Epoll engine will not be used");
+  } else {
+    gpr_log(GPR_INFO, "epoll engine will be using signal: %d",
+            grpc_wakeup_signal);
+  }
+}
+
+struct polling_island;
+
+typedef enum {
+  POLL_OBJ_FD,
+  POLL_OBJ_POLLSET,
+  POLL_OBJ_POLLSET_SET
+} poll_obj_type;
+
+typedef struct poll_obj {
+#ifdef PO_DEBUG
+  poll_obj_type obj_type;
+#endif
+  gpr_mu mu;
+  struct polling_island *pi;
+} poll_obj;
+
+static const char *poll_obj_string(poll_obj_type po_type) {
+  switch (po_type) {
+    case POLL_OBJ_FD:
+      return "fd";
+    case POLL_OBJ_POLLSET:
+      return "pollset";
+    case POLL_OBJ_POLLSET_SET:
+      return "pollset_set";
+  }
+
+  GPR_UNREACHABLE_CODE(return "UNKNOWN");
+}
+
+/*******************************************************************************
+ * Fd Declarations
+ */
+
+#define FD_FROM_PO(po) ((grpc_fd *)(po))
+
+struct grpc_fd {
+  poll_obj po;
+
+  int fd;
+  /* refst format:
+       bit 0    : 1=Active / 0=Orphaned
+       bits 1-n : refcount
+     Ref/Unref by two to avoid altering the orphaned bit */
+  gpr_atm refst;
+
+  /* The fd is either closed or we relinquished control of it. In either
+     cases, this indicates that the 'fd' on this structure is no longer
+     valid */
+  bool orphaned;
+
+  gpr_atm read_closure;
+  gpr_atm write_closure;
+
+  struct grpc_fd *freelist_next;
+  grpc_closure *on_done_closure;
+
+  /* The pollset that last noticed that the fd is readable. The actual type
+   * stored in this is (grpc_pollset *) */
+  gpr_atm read_notifier_pollset;
+
+  grpc_iomgr_object iomgr_object;
+};
+
+/* Reference counting for fds */
+// #define GRPC_FD_REF_COUNT_DEBUG
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+static void fd_ref(grpc_fd *fd, const char *reason, const char *file, int line);
+static void fd_unref(grpc_fd *fd, const char *reason, const char *file,
+                     int line);
+#define GRPC_FD_REF(fd, reason) fd_ref(fd, reason, __FILE__, __LINE__)
+#define GRPC_FD_UNREF(fd, reason) fd_unref(fd, reason, __FILE__, __LINE__)
+#else
+static void fd_ref(grpc_fd *fd);
+static void fd_unref(grpc_fd *fd);
+#define GRPC_FD_REF(fd, reason) fd_ref(fd)
+#define GRPC_FD_UNREF(fd, reason) fd_unref(fd)
+#endif
+
+static void fd_global_init(void);
+static void fd_global_shutdown(void);
+
+/*******************************************************************************
+ * Polling island Declarations
+ */
+
+#ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
+
+#define PI_ADD_REF(p, r) pi_add_ref_dbg((p), (r), __FILE__, __LINE__)
+#define PI_UNREF(exec_ctx, p, r) \
+  pi_unref_dbg((exec_ctx), (p), (r), __FILE__, __LINE__)
+
+#else /* defined(GRPC_WORKQUEUE_REFCOUNT_DEBUG) */
+
+#define PI_ADD_REF(p, r) pi_add_ref((p))
+#define PI_UNREF(exec_ctx, p, r) pi_unref((exec_ctx), (p))
+
+#endif /* !defined(GRPC_PI_REF_COUNT_DEBUG) */
+
+typedef struct worker_node {
+  struct worker_node *next;
+  struct worker_node *prev;
+} worker_node;
+
+/* This is also used as grpc_workqueue (by directly casing it) */
+typedef struct polling_island {
+  grpc_closure_scheduler workqueue_scheduler;
+
+  gpr_mu mu;
+  /* Ref count. Use PI_ADD_REF() and PI_UNREF() macros to increment/decrement
+     the refcount.
+     Once the ref count becomes zero, this structure is destroyed which means
+     we should ensure that there is never a scenario where a PI_ADD_REF() is
+     racing with a PI_UNREF() that just made the ref_count zero. */
+  gpr_atm ref_count;
+
+  /* Pointer to the polling_island this merged into.
+   * merged_to value is only set once in polling_island's lifetime (and that too
+   * only if the island is merged with another island). Because of this, we can
+   * use gpr_atm type here so that we can do atomic access on this and reduce
+   * lock contention on 'mu' mutex.
+   *
+   * Note that if this field is not NULL (i.e not 0), all the remaining fields
+   * (except mu and ref_count) are invalid and must be ignored. */
+  gpr_atm merged_to;
+
+  /* Number of threads currently polling on this island */
+  gpr_atm poller_count;
+  /* Mutex guarding the read end of the workqueue (must be held to pop from
+   * workqueue_items) */
+  gpr_mu workqueue_read_mu;
+  /* Queue of closures to be executed */
+  gpr_mpscq workqueue_items;
+  /* Count of items in workqueue_items */
+  gpr_atm workqueue_item_count;
+  /* Wakeup fd used to wake pollers to check the contents of workqueue_items */
+  grpc_wakeup_fd workqueue_wakeup_fd;
+
+  /* The list of workers waiting to do polling on this polling island */
+  gpr_mu worker_list_mu;
+  worker_node worker_list_head;
+
+  /* The fd of the underlying epoll set */
+  int epoll_fd;
+
+  /* The file descriptors in the epoll set */
+  size_t fd_cnt;
+  size_t fd_capacity;
+  grpc_fd **fds;
+} polling_island;
+
+/*******************************************************************************
+ * Pollset Declarations
+ */
+#define WORKER_FROM_WORKER_LIST_NODE(p)          \
+  (struct grpc_pollset_worker *)(((char *)(p)) - \
+                                 offsetof(grpc_pollset_worker, pi_list_link))
+struct grpc_pollset_worker {
+  /* Thread id of this worker */
+  pthread_t pt_id;
+
+  /* Used to prevent a worker from getting kicked multiple times */
+  gpr_atm is_kicked;
+
+  struct grpc_pollset_worker *next;
+  struct grpc_pollset_worker *prev;
+
+  /* Indicates if it is this worker's turn to do epoll */
+  gpr_atm is_polling_turn;
+
+  /* Node in the polling island's worker list. */
+  worker_node pi_list_link;
+};
+
+struct grpc_pollset {
+  poll_obj po;
+
+  grpc_pollset_worker root_worker;
+  bool kicked_without_pollers;
+
+  bool shutting_down;          /* Is the pollset shutting down ? */
+  bool finish_shutdown_called; /* Is the 'finish_shutdown_locked()' called ? */
+  grpc_closure *shutdown_done; /* Called after after shutdown is complete */
+};
+
+/*******************************************************************************
+ * Pollset-set Declarations
+ */
+struct grpc_pollset_set {
+  poll_obj po;
+};
+
+/*******************************************************************************
+ * Common helpers
+ */
+
+static bool append_error(grpc_error **composite, grpc_error *error,
+                         const char *desc) {
+  if (error == GRPC_ERROR_NONE) return true;
+  if (*composite == GRPC_ERROR_NONE) {
+    *composite = GRPC_ERROR_CREATE_FROM_COPIED_STRING(desc);
+  }
+  *composite = grpc_error_add_child(*composite, error);
+  return false;
+}
+
+/*******************************************************************************
+ * Polling island Definitions
+ */
+
+/* The wakeup fd that is used to wake up all threads in a Polling island. This
+   is useful in the polling island merge operation where we need to wakeup all
+   the threads currently polling the smaller polling island (so that they can
+   start polling the new/merged polling island)
+
+   NOTE: This fd is initialized to be readable and MUST NOT be consumed i.e the
+   threads that woke up MUST NOT call grpc_wakeup_fd_consume_wakeup() */
+static grpc_wakeup_fd polling_island_wakeup_fd;
+
+/* The polling island being polled right now.
+   See comments in workqueue_maybe_wakeup for why this is tracked. */
+static __thread polling_island *g_current_thread_polling_island;
+
+/* Forward declaration */
+static void polling_island_delete(grpc_exec_ctx *exec_ctx, polling_island *pi);
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                              grpc_error *error);
+
+#ifdef GRPC_TSAN
+/* Currently TSAN may incorrectly flag data races between epoll_ctl and
+   epoll_wait for any grpc_fd structs that are added to the epoll set via
+   epoll_ctl and are returned (within a very short window) via epoll_wait().
+
+   To work-around this race, we establish a happens-before relation between
+   the code just-before epoll_ctl() and the code after epoll_wait() by using
+   this atomic */
+gpr_atm g_epoll_sync;
+#endif /* defined(GRPC_TSAN) */
+
+static const grpc_closure_scheduler_vtable workqueue_scheduler_vtable = {
+    workqueue_enqueue, workqueue_enqueue, "workqueue"};
+
+static void pi_add_ref(polling_island *pi);
+static void pi_unref(grpc_exec_ctx *exec_ctx, polling_island *pi);
+
+#ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
+static void pi_add_ref_dbg(polling_island *pi, const char *reason,
+                           const char *file, int line) {
+  long old_cnt = gpr_atm_acq_load(&pi->ref_count);
+  pi_add_ref(pi);
+  gpr_log(GPR_DEBUG, "Add ref pi: %p, old: %ld -> new:%ld (%s) - (%s, %d)",
+          (void *)pi, old_cnt, old_cnt + 1, reason, file, line);
+}
+
+static void pi_unref_dbg(grpc_exec_ctx *exec_ctx, polling_island *pi,
+                         const char *reason, const char *file, int line) {
+  long old_cnt = gpr_atm_acq_load(&pi->ref_count);
+  pi_unref(exec_ctx, pi);
+  gpr_log(GPR_DEBUG, "Unref pi: %p, old:%ld -> new:%ld (%s) - (%s, %d)",
+          (void *)pi, old_cnt, (old_cnt - 1), reason, file, line);
+}
+
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue,
+                                     const char *file, int line,
+                                     const char *reason) {
+  if (workqueue != NULL) {
+    pi_add_ref_dbg((polling_island *)workqueue, reason, file, line);
+  }
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
+                            const char *file, int line, const char *reason) {
+  if (workqueue != NULL) {
+    pi_unref_dbg(exec_ctx, (polling_island *)workqueue, reason, file, line);
+  }
+}
+#else
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue) {
+  if (workqueue != NULL) {
+    pi_add_ref((polling_island *)workqueue);
+  }
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx,
+                            grpc_workqueue *workqueue) {
+  if (workqueue != NULL) {
+    pi_unref(exec_ctx, (polling_island *)workqueue);
+  }
+}
+#endif
+
+static void pi_add_ref(polling_island *pi) {
+  gpr_atm_no_barrier_fetch_add(&pi->ref_count, 1);
+}
+
+static void pi_unref(grpc_exec_ctx *exec_ctx, polling_island *pi) {
+  /* If ref count went to zero, delete the polling island.
+     Note that this deletion not be done under a lock. Once the ref count goes
+     to zero, we are guaranteed that no one else holds a reference to the
+     polling island (and that there is no racing pi_add_ref() call either).
+
+     Also, if we are deleting the polling island and the merged_to field is
+     non-empty, we should remove a ref to the merged_to polling island
+   */
+  if (1 == gpr_atm_full_fetch_add(&pi->ref_count, -1)) {
+    polling_island *next = (polling_island *)gpr_atm_acq_load(&pi->merged_to);
+    polling_island_delete(exec_ctx, pi);
+    if (next != NULL) {
+      PI_UNREF(exec_ctx, next, "pi_delete"); /* Recursive call */
+    }
+  }
+}
+
+static void worker_node_init(worker_node *node) {
+  node->next = node->prev = node;
+}
+
+/* Not thread safe. Do under a list-level lock */
+static void push_back_worker_node(worker_node *head, worker_node *node) {
+  node->next = head;
+  node->prev = head->prev;
+  head->prev->next = node;
+  head->prev = node;
+}
+
+/* Not thread safe. Do under a list-level lock */
+static void remove_worker_node(worker_node *node) {
+  node->next->prev = node->prev;
+  node->prev->next = node->next;
+  /* If node's next and prev point to itself, the node is considered detached
+   * from the list*/
+  node->next = node->prev = node;
+}
+
+/* Not thread safe. Do under a list-level lock */
+static worker_node *pop_front_worker_node(worker_node *head) {
+  worker_node *node = head->next;
+  if (node != head) {
+    remove_worker_node(node);
+  } else {
+    node = NULL;
+  }
+
+  return node;
+}
+
+/* Returns true if the node's next and prev are pointing to itself (which
+   indicates that the node is not in the list */
+static bool is_worker_node_detached(worker_node *node) {
+  return (node->next == node->prev && node->next == node);
+}
+
+/* The caller is expected to hold pi->mu lock before calling this function
+ */
+static void polling_island_add_fds_locked(polling_island *pi, grpc_fd **fds,
+                                          size_t fd_count, bool add_fd_refs,
+                                          grpc_error **error) {
+  int err;
+  size_t i;
+  struct epoll_event ev;
+  char *err_msg;
+  const char *err_desc = "polling_island_add_fds";
+
+#ifdef GRPC_TSAN
+  /* See the definition of g_epoll_sync for more context */
+  gpr_atm_rel_store(&g_epoll_sync, (gpr_atm)0);
+#endif /* defined(GRPC_TSAN) */
+
+  for (i = 0; i < fd_count; i++) {
+    ev.events = (uint32_t)(EPOLLIN | EPOLLOUT | EPOLLET);
+    ev.data.ptr = fds[i];
+    err = epoll_ctl(pi->epoll_fd, EPOLL_CTL_ADD, fds[i]->fd, &ev);
+
+    if (err < 0) {
+      if (errno != EEXIST) {
+        gpr_asprintf(
+            &err_msg,
+            "epoll_ctl (epoll_fd: %d) add fd: %d failed with error: %d (%s)",
+            pi->epoll_fd, fds[i]->fd, errno, strerror(errno));
+        append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+        gpr_free(err_msg);
+      }
+
+      continue;
+    }
+
+    if (pi->fd_cnt == pi->fd_capacity) {
+      pi->fd_capacity = GPR_MAX(pi->fd_capacity + 8, pi->fd_cnt * 3 / 2);
+      pi->fds = gpr_realloc(pi->fds, sizeof(grpc_fd *) * pi->fd_capacity);
+    }
+
+    pi->fds[pi->fd_cnt++] = fds[i];
+    if (add_fd_refs) {
+      GRPC_FD_REF(fds[i], "polling_island");
+    }
+  }
+}
+
+/* The caller is expected to hold pi->mu before calling this */
+static void polling_island_add_wakeup_fd_locked(polling_island *pi,
+                                                grpc_wakeup_fd *wakeup_fd,
+                                                grpc_error **error) {
+  struct epoll_event ev;
+  int err;
+  char *err_msg;
+  const char *err_desc = "polling_island_add_wakeup_fd";
+
+  ev.events = (uint32_t)(EPOLLIN | EPOLLET);
+  ev.data.ptr = wakeup_fd;
+  err = epoll_ctl(pi->epoll_fd, EPOLL_CTL_ADD,
+                  GRPC_WAKEUP_FD_GET_READ_FD(wakeup_fd), &ev);
+  if (err < 0 && errno != EEXIST) {
+    gpr_asprintf(&err_msg,
+                 "epoll_ctl (epoll_fd: %d) add wakeup fd: %d failed with "
+                 "error: %d (%s)",
+                 pi->epoll_fd, GRPC_WAKEUP_FD_GET_READ_FD(wakeup_fd), errno,
+                 strerror(errno));
+    append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+    gpr_free(err_msg);
+  }
+}
+
+/* The caller is expected to hold pi->mu lock before calling this function */
+static void polling_island_remove_all_fds_locked(polling_island *pi,
+                                                 bool remove_fd_refs,
+                                                 grpc_error **error) {
+  int err;
+  size_t i;
+  char *err_msg;
+  const char *err_desc = "polling_island_remove_fds";
+
+  for (i = 0; i < pi->fd_cnt; i++) {
+    err = epoll_ctl(pi->epoll_fd, EPOLL_CTL_DEL, pi->fds[i]->fd, NULL);
+    if (err < 0 && errno != ENOENT) {
+      gpr_asprintf(&err_msg,
+                   "epoll_ctl (epoll_fd: %d) delete fds[%zu]: %d failed with "
+                   "error: %d (%s)",
+                   pi->epoll_fd, i, pi->fds[i]->fd, errno, strerror(errno));
+      append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+      gpr_free(err_msg);
+    }
+
+    if (remove_fd_refs) {
+      GRPC_FD_UNREF(pi->fds[i], "polling_island");
+    }
+  }
+
+  pi->fd_cnt = 0;
+}
+
+/* The caller is expected to hold pi->mu lock before calling this function */
+static void polling_island_remove_fd_locked(polling_island *pi, grpc_fd *fd,
+                                            bool is_fd_closed,
+                                            grpc_error **error) {
+  int err;
+  size_t i;
+  char *err_msg;
+  const char *err_desc = "polling_island_remove_fd";
+
+  /* If fd is already closed, then it would have been automatically been removed
+     from the epoll set */
+  if (!is_fd_closed) {
+    err = epoll_ctl(pi->epoll_fd, EPOLL_CTL_DEL, fd->fd, NULL);
+    if (err < 0 && errno != ENOENT) {
+      gpr_asprintf(
+          &err_msg,
+          "epoll_ctl (epoll_fd: %d) del fd: %d failed with error: %d (%s)",
+          pi->epoll_fd, fd->fd, errno, strerror(errno));
+      append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+      gpr_free(err_msg);
+    }
+  }
+
+  for (i = 0; i < pi->fd_cnt; i++) {
+    if (pi->fds[i] == fd) {
+      pi->fds[i] = pi->fds[--pi->fd_cnt];
+      GRPC_FD_UNREF(fd, "polling_island");
+      break;
+    }
+  }
+}
+
+/* Might return NULL in case of an error */
+static polling_island *polling_island_create(grpc_exec_ctx *exec_ctx,
+                                             grpc_fd *initial_fd,
+                                             grpc_error **error) {
+  polling_island *pi = NULL;
+  const char *err_desc = "polling_island_create";
+
+  *error = GRPC_ERROR_NONE;
+
+  pi = gpr_malloc(sizeof(*pi));
+  pi->workqueue_scheduler.vtable = &workqueue_scheduler_vtable;
+  gpr_mu_init(&pi->mu);
+  pi->fd_cnt = 0;
+  pi->fd_capacity = 0;
+  pi->fds = NULL;
+  pi->epoll_fd = -1;
+
+  gpr_mu_init(&pi->workqueue_read_mu);
+  gpr_mpscq_init(&pi->workqueue_items);
+  gpr_atm_rel_store(&pi->workqueue_item_count, 0);
+
+  gpr_atm_rel_store(&pi->ref_count, 0);
+  gpr_atm_rel_store(&pi->poller_count, 0);
+  gpr_atm_rel_store(&pi->merged_to, (gpr_atm)NULL);
+
+  gpr_mu_init(&pi->worker_list_mu);
+  worker_node_init(&pi->worker_list_head);
+
+  if (!append_error(error, grpc_wakeup_fd_init(&pi->workqueue_wakeup_fd),
+                    err_desc)) {
+    goto done;
+  }
+
+  pi->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
+
+  if (pi->epoll_fd < 0) {
+    append_error(error, GRPC_OS_ERROR(errno, "epoll_create1"), err_desc);
+    goto done;
+  }
+
+  polling_island_add_wakeup_fd_locked(pi, &pi->workqueue_wakeup_fd, error);
+
+  if (initial_fd != NULL) {
+    polling_island_add_fds_locked(pi, &initial_fd, 1, true, error);
+  }
+
+done:
+  if (*error != GRPC_ERROR_NONE) {
+    polling_island_delete(exec_ctx, pi);
+    pi = NULL;
+  }
+  return pi;
+}
+
+static void polling_island_delete(grpc_exec_ctx *exec_ctx, polling_island *pi) {
+  GPR_ASSERT(pi->fd_cnt == 0);
+
+  if (pi->epoll_fd >= 0) {
+    close(pi->epoll_fd);
+  }
+  GPR_ASSERT(gpr_atm_no_barrier_load(&pi->workqueue_item_count) == 0);
+  gpr_mu_destroy(&pi->workqueue_read_mu);
+  gpr_mpscq_destroy(&pi->workqueue_items);
+  gpr_mu_destroy(&pi->mu);
+  grpc_wakeup_fd_destroy(&pi->workqueue_wakeup_fd);
+  gpr_mu_destroy(&pi->worker_list_mu);
+  GPR_ASSERT(is_worker_node_detached(&pi->worker_list_head));
+
+  gpr_free(pi->fds);
+  gpr_free(pi);
+}
+
+/* Attempts to gets the last polling island in the linked list (liked by the
+ * 'merged_to' field). Since this does not lock the polling island, there are no
+ * guarantees that the island returned is the last island */
+static polling_island *polling_island_maybe_get_latest(polling_island *pi) {
+  polling_island *next = (polling_island *)gpr_atm_acq_load(&pi->merged_to);
+  while (next != NULL) {
+    pi = next;
+    next = (polling_island *)gpr_atm_acq_load(&pi->merged_to);
+  }
+
+  return pi;
+}
+
+/* Gets the lock on the *latest* polling island i.e the last polling island in
+   the linked list (linked by the 'merged_to' field). Call gpr_mu_unlock on the
+   returned polling island's mu.
+   Usage: To lock/unlock polling island "pi", do the following:
+      polling_island *pi_latest = polling_island_lock(pi);
+      ...
+      ... critical section ..
+      ...
+      gpr_mu_unlock(&pi_latest->mu); // NOTE: use pi_latest->mu. NOT pi->mu */
+static polling_island *polling_island_lock(polling_island *pi) {
+  polling_island *next = NULL;
+
+  while (true) {
+    next = (polling_island *)gpr_atm_acq_load(&pi->merged_to);
+    if (next == NULL) {
+      /* Looks like 'pi' is the last node in the linked list but unless we check
+         this by holding the pi->mu lock, we cannot be sure (i.e without the
+         pi->mu lock, we don't prevent island merges).
+         To be absolutely sure, check once more by holding the pi->mu lock */
+      gpr_mu_lock(&pi->mu);
+      next = (polling_island *)gpr_atm_acq_load(&pi->merged_to);
+      if (next == NULL) {
+        /* pi is infact the last node and we have the pi->mu lock. we're done */
+        break;
+      }
+
+      /* pi->merged_to is not NULL i.e pi isn't the last node anymore. pi->mu
+       * isn't the lock we are interested in. Continue traversing the list */
+      gpr_mu_unlock(&pi->mu);
+    }
+
+    pi = next;
+  }
+
+  return pi;
+}
+
+/* Gets the lock on the *latest* polling islands in the linked lists pointed by
+   *p and *q (and also updates *p and *q to point to the latest polling islands)
+
+   This function is needed because calling the following block of code to obtain
+   locks on polling islands (*p and *q) is prone to deadlocks.
+     {
+       polling_island_lock(*p, true);
+       polling_island_lock(*q, true);
+     }
+
+   Usage/example:
+     polling_island *p1;
+     polling_island *p2;
+     ..
+     polling_island_lock_pair(&p1, &p2);
+     ..
+     .. Critical section with both p1 and p2 locked
+     ..
+     // Release locks: Always call polling_island_unlock_pair() to release locks
+     polling_island_unlock_pair(p1, p2);
+*/
+static void polling_island_lock_pair(polling_island **p, polling_island **q) {
+  polling_island *pi_1 = *p;
+  polling_island *pi_2 = *q;
+  polling_island *next_1 = NULL;
+  polling_island *next_2 = NULL;
+
+  /* The algorithm is simple:
+      - Go to the last polling islands in the linked lists *pi_1 and *pi_2 (and
+        keep updating pi_1 and pi_2)
+      - Then obtain locks on the islands by following a lock order rule of
+        locking polling_island with lower address first
+           Special case: Before obtaining the locks, check if pi_1 and pi_2 are
+           pointing to the same island. If that is the case, we can just call
+           polling_island_lock()
+      - After obtaining both the locks, double check that the polling islands
+        are still the last polling islands in their respective linked lists
+        (this is because there might have been polling island merges before
+        we got the lock)
+      - If the polling islands are the last islands, we are done. If not,
+        release the locks and continue the process from the first step */
+  while (true) {
+    next_1 = (polling_island *)gpr_atm_acq_load(&pi_1->merged_to);
+    while (next_1 != NULL) {
+      pi_1 = next_1;
+      next_1 = (polling_island *)gpr_atm_acq_load(&pi_1->merged_to);
+    }
+
+    next_2 = (polling_island *)gpr_atm_acq_load(&pi_2->merged_to);
+    while (next_2 != NULL) {
+      pi_2 = next_2;
+      next_2 = (polling_island *)gpr_atm_acq_load(&pi_2->merged_to);
+    }
+
+    if (pi_1 == pi_2) {
+      pi_1 = pi_2 = polling_island_lock(pi_1);
+      break;
+    }
+
+    if (pi_1 < pi_2) {
+      gpr_mu_lock(&pi_1->mu);
+      gpr_mu_lock(&pi_2->mu);
+    } else {
+      gpr_mu_lock(&pi_2->mu);
+      gpr_mu_lock(&pi_1->mu);
+    }
+
+    next_1 = (polling_island *)gpr_atm_acq_load(&pi_1->merged_to);
+    next_2 = (polling_island *)gpr_atm_acq_load(&pi_2->merged_to);
+    if (next_1 == NULL && next_2 == NULL) {
+      break;
+    }
+
+    gpr_mu_unlock(&pi_1->mu);
+    gpr_mu_unlock(&pi_2->mu);
+  }
+
+  *p = pi_1;
+  *q = pi_2;
+}
+
+static void polling_island_unlock_pair(polling_island *p, polling_island *q) {
+  if (p == q) {
+    gpr_mu_unlock(&p->mu);
+  } else {
+    gpr_mu_unlock(&p->mu);
+    gpr_mu_unlock(&q->mu);
+  }
+}
+
+static void workqueue_maybe_wakeup(polling_island *pi) {
+  /* If this thread is the current poller, then it may be that it's about to
+     decrement the current poller count, so we need to look past this thread */
+  bool is_current_poller = (g_current_thread_polling_island == pi);
+  gpr_atm min_current_pollers_for_wakeup = is_current_poller ? 1 : 0;
+  gpr_atm current_pollers = gpr_atm_no_barrier_load(&pi->poller_count);
+  /* Only issue a wakeup if it's likely that some poller could come in and take
+     it right now. Note that since we do an anticipatory mpscq_pop every poll
+     loop, it's ok if we miss the wakeup here, as we'll get the work item when
+     the next poller enters anyway. */
+  if (current_pollers > min_current_pollers_for_wakeup) {
+    GRPC_LOG_IF_ERROR("workqueue_wakeup_fd",
+                      grpc_wakeup_fd_wakeup(&pi->workqueue_wakeup_fd));
+  }
+}
+
+static void workqueue_move_items_to_parent(polling_island *q) {
+  polling_island *p = (polling_island *)gpr_atm_no_barrier_load(&q->merged_to);
+  if (p == NULL) {
+    return;
+  }
+  gpr_mu_lock(&q->workqueue_read_mu);
+  int num_added = 0;
+  while (gpr_atm_no_barrier_load(&q->workqueue_item_count) > 0) {
+    gpr_mpscq_node *n = gpr_mpscq_pop(&q->workqueue_items);
+    if (n != NULL) {
+      gpr_atm_no_barrier_fetch_add(&q->workqueue_item_count, -1);
+      gpr_atm_no_barrier_fetch_add(&p->workqueue_item_count, 1);
+      gpr_mpscq_push(&p->workqueue_items, n);
+      num_added++;
+    }
+  }
+  gpr_mu_unlock(&q->workqueue_read_mu);
+  if (num_added > 0) {
+    workqueue_maybe_wakeup(p);
+  }
+  workqueue_move_items_to_parent(p);
+}
+
+static polling_island *polling_island_merge(polling_island *p,
+                                            polling_island *q,
+                                            grpc_error **error) {
+  /* Get locks on both the polling islands */
+  polling_island_lock_pair(&p, &q);
+
+  if (p != q) {
+    /* Make sure that p points to the polling island with fewer fds than q */
+    if (p->fd_cnt > q->fd_cnt) {
+      GPR_SWAP(polling_island *, p, q);
+    }
+
+    /* Merge p with q i.e move all the fds from p (The one with fewer fds) to q
+       Note that the refcounts on the fds being moved will not change here.
+       This is why the last param in the following two functions is 'false') */
+    polling_island_add_fds_locked(q, p->fds, p->fd_cnt, false, error);
+    polling_island_remove_all_fds_locked(p, false, error);
+
+    /* Wakeup all the pollers (if any) on p so that they pickup this change */
+    polling_island_add_wakeup_fd_locked(p, &polling_island_wakeup_fd, error);
+
+    /* Add the 'merged_to' link from p --> q */
+    gpr_atm_rel_store(&p->merged_to, (gpr_atm)q);
+    PI_ADD_REF(q, "pi_merge"); /* To account for the new incoming ref from p */
+
+    workqueue_move_items_to_parent(p);
+  }
+  /* else if p == q, nothing needs to be done */
+
+  polling_island_unlock_pair(p, q);
+
+  /* Return the merged polling island (Note that no merge would have happened
+     if p == q which is ok) */
+  return q;
+}
+
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                              grpc_error *error) {
+  GPR_TIMER_BEGIN("workqueue.enqueue", 0);
+  grpc_workqueue *workqueue = (grpc_workqueue *)closure->scheduler;
+  /* take a ref to the workqueue: otherwise it can happen that whatever events
+   * this kicks off ends up destroying the workqueue before this function
+   * completes */
+  GRPC_WORKQUEUE_REF(workqueue, "enqueue");
+  polling_island *pi = (polling_island *)workqueue;
+  gpr_atm last = gpr_atm_no_barrier_fetch_add(&pi->workqueue_item_count, 1);
+  closure->error_data.error = error;
+  gpr_mpscq_push(&pi->workqueue_items, &closure->next_data.atm_next);
+  if (last == 0) {
+    workqueue_maybe_wakeup(pi);
+  }
+  workqueue_move_items_to_parent(pi);
+  GRPC_WORKQUEUE_UNREF(exec_ctx, workqueue, "enqueue");
+  GPR_TIMER_END("workqueue.enqueue", 0);
+}
+
+static grpc_closure_scheduler *workqueue_scheduler(grpc_workqueue *workqueue) {
+  polling_island *pi = (polling_island *)workqueue;
+  return workqueue == NULL ? grpc_schedule_on_exec_ctx
+                           : &pi->workqueue_scheduler;
+}
+
+static grpc_error *polling_island_global_init() {
+  grpc_error *error = GRPC_ERROR_NONE;
+
+  error = grpc_wakeup_fd_init(&polling_island_wakeup_fd);
+  if (error == GRPC_ERROR_NONE) {
+    error = grpc_wakeup_fd_wakeup(&polling_island_wakeup_fd);
+  }
+
+  return error;
+}
+
+static void polling_island_global_shutdown() {
+  grpc_wakeup_fd_destroy(&polling_island_wakeup_fd);
+}
+
+/*******************************************************************************
+ * Fd Definitions
+ */
+
+/* We need to keep a freelist not because of any concerns of malloc performance
+ * but instead so that implementations with multiple threads in (for example)
+ * epoll_wait deal with the race between pollset removal and incoming poll
+ * notifications.
+ *
+ * The problem is that the poller ultimately holds a reference to this
+ * object, so it is very difficult to know when is safe to free it, at least
+ * without some expensive synchronization.
+ *
+ * If we keep the object freelisted, in the worst case losing this race just
+ * becomes a spurious read notification on a reused fd.
+ */
+
+/* The alarm system needs to be able to wakeup 'some poller' sometimes
+ * (specifically when a new alarm needs to be triggered earlier than the next
+ * alarm 'epoch'). This wakeup_fd gives us something to alert on when such a
+ * case occurs. */
+
+static grpc_fd *fd_freelist = NULL;
+static gpr_mu fd_freelist_mu;
+
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+#define REF_BY(fd, n, reason) ref_by(fd, n, reason, __FILE__, __LINE__)
+#define UNREF_BY(fd, n, reason) unref_by(fd, n, reason, __FILE__, __LINE__)
+static void ref_by(grpc_fd *fd, int n, const char *reason, const char *file,
+                   int line) {
+  gpr_log(GPR_DEBUG, "FD %d %p   ref %d %ld -> %ld [%s; %s:%d]", fd->fd,
+          (void *)fd, n, gpr_atm_no_barrier_load(&fd->refst),
+          gpr_atm_no_barrier_load(&fd->refst) + n, reason, file, line);
+#else
+#define REF_BY(fd, n, reason) ref_by(fd, n)
+#define UNREF_BY(fd, n, reason) unref_by(fd, n)
+static void ref_by(grpc_fd *fd, int n) {
+#endif
+  GPR_ASSERT(gpr_atm_no_barrier_fetch_add(&fd->refst, n) > 0);
+}
+
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+static void unref_by(grpc_fd *fd, int n, const char *reason, const char *file,
+                     int line) {
+  gpr_atm old;
+  gpr_log(GPR_DEBUG, "FD %d %p unref %d %ld -> %ld [%s; %s:%d]", fd->fd,
+          (void *)fd, n, gpr_atm_no_barrier_load(&fd->refst),
+          gpr_atm_no_barrier_load(&fd->refst) - n, reason, file, line);
+#else
+static void unref_by(grpc_fd *fd, int n) {
+  gpr_atm old;
+#endif
+  old = gpr_atm_full_fetch_add(&fd->refst, -n);
+  if (old == n) {
+    /* Add the fd to the freelist */
+    gpr_mu_lock(&fd_freelist_mu);
+    fd->freelist_next = fd_freelist;
+    fd_freelist = fd;
+    grpc_iomgr_unregister_object(&fd->iomgr_object);
+
+    grpc_lfev_destroy(&fd->read_closure);
+    grpc_lfev_destroy(&fd->write_closure);
+
+    gpr_mu_unlock(&fd_freelist_mu);
+  } else {
+    GPR_ASSERT(old > n);
+  }
+}
+
+/* Increment refcount by two to avoid changing the orphan bit */
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+static void fd_ref(grpc_fd *fd, const char *reason, const char *file,
+                   int line) {
+  ref_by(fd, 2, reason, file, line);
+}
+
+static void fd_unref(grpc_fd *fd, const char *reason, const char *file,
+                     int line) {
+  unref_by(fd, 2, reason, file, line);
+}
+#else
+static void fd_ref(grpc_fd *fd) { ref_by(fd, 2); }
+static void fd_unref(grpc_fd *fd) { unref_by(fd, 2); }
+#endif
+
+static void fd_global_init(void) { gpr_mu_init(&fd_freelist_mu); }
+
+static void fd_global_shutdown(void) {
+  gpr_mu_lock(&fd_freelist_mu);
+  gpr_mu_unlock(&fd_freelist_mu);
+  while (fd_freelist != NULL) {
+    grpc_fd *fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+    gpr_mu_destroy(&fd->po.mu);
+    gpr_free(fd);
+  }
+  gpr_mu_destroy(&fd_freelist_mu);
+}
+
+static grpc_fd *fd_create(int fd, const char *name) {
+  grpc_fd *new_fd = NULL;
+
+  gpr_mu_lock(&fd_freelist_mu);
+  if (fd_freelist != NULL) {
+    new_fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+  }
+  gpr_mu_unlock(&fd_freelist_mu);
+
+  if (new_fd == NULL) {
+    new_fd = gpr_malloc(sizeof(grpc_fd));
+    gpr_mu_init(&new_fd->po.mu);
+  }
+
+  /* Note: It is not really needed to get the new_fd->po.mu lock here. If this
+   * is a newly created fd (or an fd we got from the freelist), no one else
+   * would be holding a lock to it anyway. */
+  gpr_mu_lock(&new_fd->po.mu);
+  new_fd->po.pi = NULL;
+#ifdef PO_DEBUG
+  new_fd->po.obj_type = POLL_OBJ_FD;
+#endif
+
+  gpr_atm_rel_store(&new_fd->refst, (gpr_atm)1);
+  new_fd->fd = fd;
+  new_fd->orphaned = false;
+  grpc_lfev_init(&new_fd->read_closure);
+  grpc_lfev_init(&new_fd->write_closure);
+  gpr_atm_no_barrier_store(&new_fd->read_notifier_pollset, (gpr_atm)NULL);
+
+  new_fd->freelist_next = NULL;
+  new_fd->on_done_closure = NULL;
+
+  gpr_mu_unlock(&new_fd->po.mu);
+
+  char *fd_name;
+  gpr_asprintf(&fd_name, "%s fd=%d", name, fd);
+  grpc_iomgr_register_object(&new_fd->iomgr_object, fd_name);
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+  gpr_log(GPR_DEBUG, "FD %d %p create %s", fd, (void *)new_fd, fd_name);
+#endif
+  gpr_free(fd_name);
+  return new_fd;
+}
+
+static int fd_wrapped_fd(grpc_fd *fd) {
+  int ret_fd = -1;
+  gpr_mu_lock(&fd->po.mu);
+  if (!fd->orphaned) {
+    ret_fd = fd->fd;
+  }
+  gpr_mu_unlock(&fd->po.mu);
+
+  return ret_fd;
+}
+
+static void fd_orphan(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                      grpc_closure *on_done, int *release_fd,
+                      const char *reason) {
+  bool is_fd_closed = false;
+  grpc_error *error = GRPC_ERROR_NONE;
+  polling_island *unref_pi = NULL;
+
+  gpr_mu_lock(&fd->po.mu);
+  fd->on_done_closure = on_done;
+
+  /* If release_fd is not NULL, we should be relinquishing control of the file
+     descriptor fd->fd (but we still own the grpc_fd structure). */
+  if (release_fd != NULL) {
+    *release_fd = fd->fd;
+  } else {
+    close(fd->fd);
+    is_fd_closed = true;
+  }
+
+  fd->orphaned = true;
+
+  /* Remove the active status but keep referenced. We want this grpc_fd struct
+     to be alive (and not added to freelist) until the end of this function */
+  REF_BY(fd, 1, reason);
+
+  /* Remove the fd from the polling island:
+     - Get a lock on the latest polling island (i.e the last island in the
+       linked list pointed by fd->po.pi). This is the island that
+       would actually contain the fd
+     - Remove the fd from the latest polling island
+     - Unlock the latest polling island
+     - Set fd->po.pi to NULL (but remove the ref on the polling island
+       before doing this.) */
+  if (fd->po.pi != NULL) {
+    polling_island *pi_latest = polling_island_lock(fd->po.pi);
+    polling_island_remove_fd_locked(pi_latest, fd, is_fd_closed, &error);
+    gpr_mu_unlock(&pi_latest->mu);
+
+    unref_pi = fd->po.pi;
+    fd->po.pi = NULL;
+  }
+
+  grpc_closure_sched(exec_ctx, fd->on_done_closure, GRPC_ERROR_REF(error));
+
+  gpr_mu_unlock(&fd->po.mu);
+  UNREF_BY(fd, 2, reason); /* Drop the reference */
+  if (unref_pi != NULL) {
+    /* Unref stale polling island here, outside the fd lock above.
+       The polling island owns a workqueue which owns an fd, and unreffing
+       inside the lock can cause an eventual lock loop that makes TSAN very
+       unhappy. */
+    PI_UNREF(exec_ctx, unref_pi, "fd_orphan");
+  }
+  GRPC_LOG_IF_ERROR("fd_orphan", GRPC_ERROR_REF(error));
+  GRPC_ERROR_UNREF(error);
+}
+
+static grpc_pollset *fd_get_read_notifier_pollset(grpc_exec_ctx *exec_ctx,
+                                                  grpc_fd *fd) {
+  gpr_atm notifier = gpr_atm_acq_load(&fd->read_notifier_pollset);
+  return (grpc_pollset *)notifier;
+}
+
+static bool fd_is_shutdown(grpc_fd *fd) {
+  return grpc_lfev_is_shutdown(&fd->read_closure);
+}
+
+/* Might be called multiple times */
+static void fd_shutdown(grpc_exec_ctx *exec_ctx, grpc_fd *fd, grpc_error *why) {
+  if (grpc_lfev_set_shutdown(exec_ctx, &fd->read_closure,
+                             GRPC_ERROR_REF(why))) {
+    shutdown(fd->fd, SHUT_RDWR);
+    grpc_lfev_set_shutdown(exec_ctx, &fd->write_closure, GRPC_ERROR_REF(why));
+  }
+  GRPC_ERROR_UNREF(why);
+}
+
+static void fd_notify_on_read(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                              grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->read_closure, closure);
+}
+
+static void fd_notify_on_write(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                               grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->write_closure, closure);
+}
+
+static grpc_workqueue *fd_get_workqueue(grpc_fd *fd) {
+  gpr_mu_lock(&fd->po.mu);
+  grpc_workqueue *workqueue =
+      GRPC_WORKQUEUE_REF((grpc_workqueue *)fd->po.pi, "fd_get_workqueue");
+  gpr_mu_unlock(&fd->po.mu);
+  return workqueue;
+}
+
+/*******************************************************************************
+ * Pollset Definitions
+ */
+GPR_TLS_DECL(g_current_thread_pollset);
+GPR_TLS_DECL(g_current_thread_worker);
+static __thread bool g_initialized_sigmask;
+static __thread sigset_t g_orig_sigmask;
+static __thread sigset_t g_wakeup_sig_set;
+
+static void sig_handler(int sig_num) {
+#ifdef GRPC_EPOLL_DEBUG
+  gpr_log(GPR_INFO, "Received signal %d", sig_num);
+#endif
+}
+
+static void pollset_worker_init(grpc_pollset_worker *worker) {
+  worker->pt_id = pthread_self();
+  worker->next = worker->prev = NULL;
+  gpr_atm_no_barrier_store(&worker->is_kicked, (gpr_atm)0);
+  gpr_atm_no_barrier_store(&worker->is_polling_turn, (gpr_atm)0);
+  worker_node_init(&worker->pi_list_link);
+}
+
+static void poller_kick_init() { signal(grpc_wakeup_signal, sig_handler); }
+
+/* Global state management */
+static grpc_error *pollset_global_init(void) {
+  gpr_tls_init(&g_current_thread_pollset);
+  gpr_tls_init(&g_current_thread_worker);
+  poller_kick_init();
+  return GRPC_ERROR_NONE;
+}
+
+static void pollset_global_shutdown(void) {
+  gpr_tls_destroy(&g_current_thread_pollset);
+  gpr_tls_destroy(&g_current_thread_worker);
+}
+
+static grpc_error *worker_kick(grpc_pollset_worker *worker,
+                               gpr_atm *is_kicked) {
+  grpc_error *err = GRPC_ERROR_NONE;
+
+  /* Kick the worker only if it was not already kicked */
+  if (gpr_atm_no_barrier_cas(is_kicked, (gpr_atm)0, (gpr_atm)1)) {
+    GRPC_POLLING_TRACE(
+        "pollset_worker_kick: Kicking worker: %p (thread id: %ld)",
+        (void *)worker, (long int)worker->pt_id);
+    int err_num = pthread_kill(worker->pt_id, grpc_wakeup_signal);
+    if (err_num != 0) {
+      err = GRPC_OS_ERROR(err_num, "pthread_kill");
+    }
+  }
+  return err;
+}
+
+static grpc_error *pollset_worker_kick(grpc_pollset_worker *worker) {
+  return worker_kick(worker, &worker->is_kicked);
+}
+
+static grpc_error *poller_kick(grpc_pollset_worker *worker) {
+  return worker_kick(worker, &worker->is_polling_turn);
+}
+
+/* Return 1 if the pollset has active threads in pollset_work (pollset must
+ * be locked) */
+static int pollset_has_workers(grpc_pollset *p) {
+  return p->root_worker.next != &p->root_worker;
+}
+
+static void remove_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
+  worker->prev->next = worker->next;
+  worker->next->prev = worker->prev;
+}
+
+static grpc_pollset_worker *pop_front_worker(grpc_pollset *p) {
+  if (pollset_has_workers(p)) {
+    grpc_pollset_worker *w = p->root_worker.next;
+    remove_worker(p, w);
+    return w;
+  } else {
+    return NULL;
+  }
+}
+
+static void push_back_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
+  worker->next = &p->root_worker;
+  worker->prev = worker->next->prev;
+  worker->prev->next = worker->next->prev = worker;
+}
+
+static void push_front_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
+  worker->prev = &p->root_worker;
+  worker->next = worker->prev->next;
+  worker->prev->next = worker->next->prev = worker;
+}
+
+/* p->mu must be held before calling this function */
+static grpc_error *pollset_kick(grpc_pollset *p,
+                                grpc_pollset_worker *specific_worker) {
+  GPR_TIMER_BEGIN("pollset_kick", 0);
+  grpc_error *error = GRPC_ERROR_NONE;
+  const char *err_desc = "Kick Failure";
+  grpc_pollset_worker *worker = specific_worker;
+  if (worker != NULL) {
+    if (worker == GRPC_POLLSET_KICK_BROADCAST) {
+      if (pollset_has_workers(p)) {
+        GPR_TIMER_BEGIN("pollset_kick.broadcast", 0);
+        for (worker = p->root_worker.next; worker != &p->root_worker;
+             worker = worker->next) {
+          if (gpr_tls_get(&g_current_thread_worker) != (intptr_t)worker) {
+            append_error(&error, pollset_worker_kick(worker), err_desc);
+          }
+        }
+        GPR_TIMER_END("pollset_kick.broadcast", 0);
+      } else {
+        p->kicked_without_pollers = true;
+      }
+    } else {
+      GPR_TIMER_MARK("kicked_specifically", 0);
+      if (gpr_tls_get(&g_current_thread_worker) != (intptr_t)worker) {
+        append_error(&error, pollset_worker_kick(worker), err_desc);
+      }
+    }
+  } else if (gpr_tls_get(&g_current_thread_pollset) != (intptr_t)p) {
+    /* Since worker == NULL, it means that we can kick "any" worker on this
+       pollset 'p'. If 'p' happens to be the same pollset this thread is
+       currently polling (i.e in pollset_work() function), then there is no need
+       to kick any other worker since the current thread can just absorb the
+       kick. This is the reason why we enter this case only when
+       g_current_thread_pollset is != p */
+
+    GPR_TIMER_MARK("kick_anonymous", 0);
+    worker = pop_front_worker(p);
+    if (worker != NULL) {
+      GPR_TIMER_MARK("finally_kick", 0);
+      push_back_worker(p, worker);
+      append_error(&error, pollset_worker_kick(worker), err_desc);
+    } else {
+      GPR_TIMER_MARK("kicked_no_pollers", 0);
+      p->kicked_without_pollers = true;
+    }
+  }
+
+  GPR_TIMER_END("pollset_kick", 0);
+  GRPC_LOG_IF_ERROR("pollset_kick", GRPC_ERROR_REF(error));
+  return error;
+}
+
+static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
+  gpr_mu_init(&pollset->po.mu);
+  *mu = &pollset->po.mu;
+  pollset->po.pi = NULL;
+#ifdef PO_DEBUG
+  pollset->po.obj_type = POLL_OBJ_POLLSET;
+#endif
+
+  pollset->root_worker.next = pollset->root_worker.prev = &pollset->root_worker;
+  pollset->kicked_without_pollers = false;
+
+  pollset->shutting_down = false;
+  pollset->finish_shutdown_called = false;
+  pollset->shutdown_done = NULL;
+}
+
+/* Convert millis to timespec (clock-type is assumed to be GPR_TIMESPAN) */
+static struct timespec millis_to_timespec(int millis) {
+  struct timespec linux_ts;
+  gpr_timespec gpr_ts;
+
+  if (millis == -1) {
+    gpr_ts = gpr_inf_future(GPR_TIMESPAN);
+  } else {
+    gpr_ts = gpr_time_from_millis(millis, GPR_TIMESPAN);
+  }
+
+  linux_ts.tv_sec = (time_t)gpr_ts.tv_sec;
+  linux_ts.tv_nsec = gpr_ts.tv_nsec;
+  return linux_ts;
+}
+
+/* Convert a timespec to milliseconds:
+   - Very small or negative poll times are clamped to zero to do a non-blocking
+     poll (which becomes spin polling)
+   - Other small values are rounded up to one millisecond
+   - Longer than a millisecond polls are rounded up to the next nearest
+     millisecond to avoid spinning
+   - Infinite timeouts are converted to -1 */
+static int poll_deadline_to_millis_timeout(gpr_timespec deadline,
+                                           gpr_timespec now) {
+  gpr_timespec timeout;
+  static const int64_t max_spin_polling_us = 10;
+  if (gpr_time_cmp(deadline, gpr_inf_future(deadline.clock_type)) == 0) {
+    return -1;
+  }
+
+  if (gpr_time_cmp(deadline, gpr_time_add(now, gpr_time_from_micros(
+                                                   max_spin_polling_us,
+                                                   GPR_TIMESPAN))) <= 0) {
+    return 0;
+  }
+  timeout = gpr_time_sub(deadline, now);
+  int millis = gpr_time_to_millis(gpr_time_add(
+      timeout, gpr_time_from_nanos(GPR_NS_PER_MS - 1, GPR_TIMESPAN)));
+  return millis >= 1 ? millis : 1;
+}
+
+static void fd_become_readable(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                               grpc_pollset *notifier) {
+  grpc_lfev_set_ready(exec_ctx, &fd->read_closure);
+
+  /* Note, it is possible that fd_become_readable might be called twice with
+     different 'notifier's when an fd becomes readable and it is in two epoll
+     sets (This can happen briefly during polling island merges). In such cases
+     it does not really matter which notifer is set as the read_notifier_pollset
+     (They would both point to the same polling island anyway) */
+  /* Use release store to match with acquire load in fd_get_read_notifier */
+  gpr_atm_rel_store(&fd->read_notifier_pollset, (gpr_atm)notifier);
+}
+
+static void fd_become_writable(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
+  grpc_lfev_set_ready(exec_ctx, &fd->write_closure);
+}
+
+static void pollset_release_polling_island(grpc_exec_ctx *exec_ctx,
+                                           grpc_pollset *ps, char *reason) {
+  if (ps->po.pi != NULL) {
+    PI_UNREF(exec_ctx, ps->po.pi, reason);
+  }
+  ps->po.pi = NULL;
+}
+
+static void finish_shutdown_locked(grpc_exec_ctx *exec_ctx,
+                                   grpc_pollset *pollset) {
+  /* The pollset cannot have any workers if we are at this stage */
+  GPR_ASSERT(!pollset_has_workers(pollset));
+
+  pollset->finish_shutdown_called = true;
+
+  /* Release the ref and set pollset->po.pi to NULL */
+  pollset_release_polling_island(exec_ctx, pollset, "ps_shutdown");
+  grpc_closure_sched(exec_ctx, pollset->shutdown_done, GRPC_ERROR_NONE);
+}
+
+/* pollset->po.mu lock must be held by the caller before calling this */
+static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                             grpc_closure *closure) {
+  GPR_TIMER_BEGIN("pollset_shutdown", 0);
+  GPR_ASSERT(!pollset->shutting_down);
+  pollset->shutting_down = true;
+  pollset->shutdown_done = closure;
+  pollset_kick(pollset, GRPC_POLLSET_KICK_BROADCAST);
+
+  /* If the pollset has any workers, we cannot call finish_shutdown_locked()
+     because it would release the underlying polling island. In such a case, we
+     let the last worker call finish_shutdown_locked() from pollset_work() */
+  if (!pollset_has_workers(pollset)) {
+    GPR_ASSERT(!pollset->finish_shutdown_called);
+    GPR_TIMER_MARK("pollset_shutdown.finish_shutdown_locked", 0);
+    finish_shutdown_locked(exec_ctx, pollset);
+  }
+  GPR_TIMER_END("pollset_shutdown", 0);
+}
+
+/* pollset_shutdown is guaranteed to be called before pollset_destroy. So other
+ * than destroying the mutexes, there is nothing special that needs to be done
+ * here */
+static void pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
+  GPR_ASSERT(!pollset_has_workers(pollset));
+  gpr_mu_destroy(&pollset->po.mu);
+}
+
+static bool maybe_do_workqueue_work(grpc_exec_ctx *exec_ctx,
+                                    polling_island *pi) {
+  if (gpr_mu_trylock(&pi->workqueue_read_mu)) {
+    gpr_mpscq_node *n = gpr_mpscq_pop(&pi->workqueue_items);
+    gpr_mu_unlock(&pi->workqueue_read_mu);
+    if (n != NULL) {
+      if (gpr_atm_full_fetch_add(&pi->workqueue_item_count, -1) > 1) {
+        workqueue_maybe_wakeup(pi);
+      }
+      grpc_closure *c = (grpc_closure *)n;
+      grpc_error *error = c->error_data.error;
+#ifndef NDEBUG
+      c->scheduled = false;
+#endif
+      c->cb(exec_ctx, c->cb_arg, error);
+      GRPC_ERROR_UNREF(error);
+      return true;
+    } else if (gpr_atm_no_barrier_load(&pi->workqueue_item_count) > 0) {
+      /* n == NULL might mean there's work but it's not available to be popped
+       * yet - try to ensure another workqueue wakes up to check shortly if so
+       */
+      workqueue_maybe_wakeup(pi);
+    }
+  }
+  return false;
+}
+
+/* NOTE: This function may modify 'now' */
+static bool acquire_polling_lease(grpc_pollset_worker *worker,
+                                  polling_island *pi, gpr_timespec deadline,
+                                  gpr_timespec *now) {
+  bool is_lease_acquired = false;
+
+  gpr_mu_lock(&pi->worker_list_mu);  //  LOCK
+  long num_pollers = gpr_atm_no_barrier_load(&pi->poller_count);
+
+  if (num_pollers >= g_max_pollers_per_pi) {
+    push_back_worker_node(&pi->worker_list_head, &worker->pi_list_link);
+    gpr_mu_unlock(&pi->worker_list_mu);  // UNLOCK
+
+    bool is_timeout = false;
+    int ret;
+    int timeout_ms = poll_deadline_to_millis_timeout(deadline, *now);
+    if (timeout_ms == -1) {
+      ret = sigwaitinfo(&g_wakeup_sig_set, NULL);
+    } else {
+      struct timespec sigwait_timeout = millis_to_timespec(timeout_ms);
+      GRPC_SCHEDULING_START_BLOCKING_REGION;
+      ret = sigtimedwait(&g_wakeup_sig_set, NULL, &sigwait_timeout);
+      GRPC_SCHEDULING_END_BLOCKING_REGION;
+    }
+
+    if (ret == -1) {
+      if (errno == EAGAIN) {
+        is_timeout = true;
+      } else {
+        /* NOTE: This should not happen. If we see these log messages, it means
+           we are most likely doing something incorrect in the setup * needed
+           for sigwaitinfo/sigtimedwait */
+        gpr_log(GPR_ERROR,
+                "sigtimedwait failed with retcode: %d (timeout_ms: %d)", errno,
+                timeout_ms);
+      }
+    }
+
+    /* Did the worker come out of sigtimedwait due to a thread that just
+       exited epoll and kicking it (in release_polling_lease function). */
+    bool is_polling_turn = gpr_atm_acq_load(&worker->is_polling_turn);
+
+    /* Did the worker come out of sigtimedwait due to a thread alerting it that
+       some completion event was (likely) available in the completion queue */
+    bool is_kicked = gpr_atm_no_barrier_load(&worker->is_kicked);
+
+    if (is_kicked || is_timeout) {
+      *now = deadline; /* Essentially make the epoll timeout = 0 */
+    } else if (is_polling_turn) {
+      *now = gpr_now(GPR_CLOCK_MONOTONIC); /* Reduce the epoll timeout */
+    }
+
+    gpr_mu_lock(&pi->worker_list_mu);  // LOCK
+    /* The node might have already been removed from the list by the poller
+       that kicked this. However it is safe to call 'remove_worker_node' on
+       an already detached node */
+    remove_worker_node(&worker->pi_list_link);
+    /* It is important to read the num_pollers again under the lock so that we
+     * have the latest num_pollers value that doesn't change while we are doing
+     * the "(num_pollers < g_max_pollers_per_pi)" a a few lines below */
+    num_pollers = gpr_atm_no_barrier_load(&pi->poller_count);
+  }
+
+  if (num_pollers < g_max_pollers_per_pi) {
+    gpr_atm_no_barrier_fetch_add(&pi->poller_count, 1);
+    is_lease_acquired = true;
+  }
+
+  gpr_mu_unlock(&pi->worker_list_mu);  // UNLOCK
+  return is_lease_acquired;
+}
+
+static void release_polling_lease(polling_island *pi, grpc_error **error) {
+  gpr_mu_lock(&pi->worker_list_mu);
+
+  gpr_atm_no_barrier_fetch_add(&pi->poller_count, -1);
+  worker_node *node = pop_front_worker_node(&pi->worker_list_head);
+  if (node != NULL) {
+    grpc_pollset_worker *next_worker = WORKER_FROM_WORKER_LIST_NODE(node);
+    append_error(error, poller_kick(next_worker), "poller kick error");
+  }
+
+  gpr_mu_unlock(&pi->worker_list_mu);
+}
+
+#define GRPC_EPOLL_MAX_EVENTS 100
+static void pollset_do_epoll_pwait(grpc_exec_ctx *exec_ctx, int epoll_fd,
+                                   grpc_pollset *pollset, polling_island *pi,
+                                   grpc_pollset_worker *worker,
+                                   gpr_timespec now, gpr_timespec deadline,
+                                   sigset_t *sig_mask, grpc_error **error) {
+  /* Only g_max_pollers_per_pi threads can be doing polling in parallel.
+     If we cannot get a lease, we cannot continue to do epoll_pwait() */
+  if (!acquire_polling_lease(worker, pi, deadline, &now)) {
+    return;
+  }
+
+  struct epoll_event ep_ev[GRPC_EPOLL_MAX_EVENTS];
+  int ep_rv;
+  char *err_msg;
+  const char *err_desc = "pollset_work_and_unlock";
+
+  /* timeout_ms is the time between 'now' and 'deadline' */
+  int timeout_ms = poll_deadline_to_millis_timeout(deadline, now);
+
+  GRPC_SCHEDULING_START_BLOCKING_REGION;
+  ep_rv =
+      epoll_pwait(epoll_fd, ep_ev, GRPC_EPOLL_MAX_EVENTS, timeout_ms, sig_mask);
+  GRPC_SCHEDULING_END_BLOCKING_REGION;
+
+  /* Give back the lease right away so that some other thread can enter */
+  release_polling_lease(pi, error);
+
+  if (ep_rv < 0) {
+    if (errno != EINTR) {
+      gpr_asprintf(&err_msg,
+                   "epoll_wait() epoll fd: %d failed with error: %d (%s)",
+                   epoll_fd, errno, strerror(errno));
+      append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+    } else {
+      /* We were interrupted. Save an interation by doing a zero timeout
+         epoll_wait to see if there are any other events of interest */
+      GRPC_POLLING_TRACE("pollset_work: pollset: %p, worker: %p received kick",
+                         (void *)pollset, (void *)worker);
+      ep_rv = epoll_wait(epoll_fd, ep_ev, GRPC_EPOLL_MAX_EVENTS, 0);
+    }
+  }
+
+#ifdef GRPC_TSAN
+  /* See the definition of g_poll_sync for more details */
+  gpr_atm_acq_load(&g_epoll_sync);
+#endif /* defined(GRPC_TSAN) */
+
+  for (int i = 0; i < ep_rv; ++i) {
+    void *data_ptr = ep_ev[i].data.ptr;
+    if (data_ptr == &pi->workqueue_wakeup_fd) {
+      append_error(error,
+                   grpc_wakeup_fd_consume_wakeup(&pi->workqueue_wakeup_fd),
+                   err_desc);
+      maybe_do_workqueue_work(exec_ctx, pi);
+    } else if (data_ptr == &polling_island_wakeup_fd) {
+      GRPC_POLLING_TRACE(
+          "pollset_work: pollset: %p, worker: %p polling island (epoll_fd: "
+          "%d) got merged",
+          (void *)pollset, (void *)worker, epoll_fd);
+      /* This means that our polling island is merged with a different
+         island. We do not have to do anything here since the subsequent call
+         to the function pollset_work_and_unlock() will pick up the correct
+         epoll_fd */
+    } else {
+      grpc_fd *fd = data_ptr;
+      int cancel = ep_ev[i].events & (EPOLLERR | EPOLLHUP);
+      int read_ev = ep_ev[i].events & (EPOLLIN | EPOLLPRI);
+      int write_ev = ep_ev[i].events & EPOLLOUT;
+      if (read_ev || cancel) {
+        fd_become_readable(exec_ctx, fd, pollset);
+      }
+      if (write_ev || cancel) {
+        fd_become_writable(exec_ctx, fd);
+      }
+    }
+  }
+}
+
+/* Note: sig_mask contains the signal mask to use *during* epoll_wait() */
+static void pollset_work_and_unlock(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset *pollset,
+                                    grpc_pollset_worker *worker,
+                                    gpr_timespec now, gpr_timespec deadline,
+                                    sigset_t *sig_mask, grpc_error **error) {
+  int epoll_fd = -1;
+  polling_island *pi = NULL;
+  GPR_TIMER_BEGIN("pollset_work_and_unlock", 0);
+
+  /* We need to get the epoll_fd to wait on. The epoll_fd is in inside the
+     latest polling island pointed by pollset->po.pi
+
+     Since epoll_fd is immutable, it is safe to read it without a lock on the
+     polling island. There is however a possibility that the polling island from
+     which we got the epoll_fd, got merged with another island in the meantime.
+     This is okay because in such a case, we will wakeup right-away from
+     epoll_pwait() (because any merge will poison the old polling island's epoll
+     set 'polling_island_wakeup_fd') and then pick up the latest polling_island
+     the next time this function - pollset_work_and_unlock()) is called */
+
+  if (pollset->po.pi == NULL) {
+    pollset->po.pi = polling_island_create(exec_ctx, NULL, error);
+    if (pollset->po.pi == NULL) {
+      GPR_TIMER_END("pollset_work_and_unlock", 0);
+      return; /* Fatal error. Cannot continue */
+    }
+
+    PI_ADD_REF(pollset->po.pi, "ps");
+    GRPC_POLLING_TRACE("pollset_work: pollset: %p created new pi: %p",
+                       (void *)pollset, (void *)pollset->po.pi);
+  }
+
+  pi = polling_island_maybe_get_latest(pollset->po.pi);
+  epoll_fd = pi->epoll_fd;
+
+  /* Update the pollset->po.pi since the island being pointed by
+     pollset->po.pi maybe older than the one pointed by pi) */
+  if (pollset->po.pi != pi) {
+    /* Always do PI_ADD_REF before PI_UNREF because PI_UNREF may cause the
+       polling island to be deleted */
+    PI_ADD_REF(pi, "ps");
+    PI_UNREF(exec_ctx, pollset->po.pi, "ps");
+    pollset->po.pi = pi;
+  }
+
+  /* Add an extra ref so that the island does not get destroyed (which means
+     the epoll_fd won't be closed) while we are are doing an epoll_wait() on the
+     epoll_fd */
+  PI_ADD_REF(pi, "ps_work");
+  gpr_mu_unlock(&pollset->po.mu);
+
+  /* If we get some workqueue work to do, it might end up completing an item on
+     the completion queue, so there's no need to poll... so we skip that and
+     redo the complete loop to verify */
+  if (!maybe_do_workqueue_work(exec_ctx, pi)) {
+    g_current_thread_polling_island = pi;
+    pollset_do_epoll_pwait(exec_ctx, epoll_fd, pollset, pi, worker, now,
+                           deadline, sig_mask, error);
+    g_current_thread_polling_island = NULL;
+  }
+
+  GPR_ASSERT(pi != NULL);
+
+  /* Before leaving, release the extra ref we added to the polling island. It
+     is important to use "pi" here (i.e our old copy of pollset->po.pi
+     that we got before releasing the polling island lock). This is because
+     pollset->po.pi pointer might get udpated in other parts of the
+     code when there is an island merge while we are doing epoll_wait() above */
+  PI_UNREF(exec_ctx, pi, "ps_work");
+
+  GPR_TIMER_END("pollset_work_and_unlock", 0);
+}
+
+/* pollset->po.mu lock must be held by the caller before calling this.
+   The function pollset_work() may temporarily release the lock (pollset->po.mu)
+   during the course of its execution but it will always re-acquire the lock and
+   ensure that it is held by the time the function returns */
+static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                                grpc_pollset_worker **worker_hdl,
+                                gpr_timespec now, gpr_timespec deadline) {
+  GPR_TIMER_BEGIN("pollset_work", 0);
+  grpc_error *error = GRPC_ERROR_NONE;
+
+  grpc_pollset_worker worker;
+  pollset_worker_init(&worker);
+
+  if (worker_hdl) *worker_hdl = &worker;
+
+  gpr_tls_set(&g_current_thread_pollset, (intptr_t)pollset);
+  gpr_tls_set(&g_current_thread_worker, (intptr_t)&worker);
+
+  if (pollset->kicked_without_pollers) {
+    /* If the pollset was kicked without pollers, pretend that the current
+       worker got the kick and skip polling. A kick indicates that there is some
+       work that needs attention like an event on the completion queue or an
+       alarm */
+    GPR_TIMER_MARK("pollset_work.kicked_without_pollers", 0);
+    pollset->kicked_without_pollers = 0;
+  } else if (!pollset->shutting_down) {
+    /* We use the posix-signal with number 'grpc_wakeup_signal' for waking up
+       (i.e 'kicking') a worker in the pollset. A 'kick' is a way to inform the
+       worker that there is some pending work that needs immediate attention
+       (like an event on the completion queue, or a polling island merge that
+       results in a new epoll-fd to wait on) and that the worker should not
+       spend time waiting in epoll_pwait().
+
+       A worker can be kicked anytime from the point it is added to the pollset
+       via push_front_worker() (or push_back_worker()) to the point it is
+       removed via remove_worker().
+       If the worker is kicked before/during it calls epoll_pwait(), it should
+       immediately exit from epoll_wait(). If the worker is kicked after it
+       returns from epoll_wait(), then nothing really needs to be done.
+
+       To accomplish this, we mask 'grpc_wakeup_signal' on this thread at all
+       times *except* when it is in epoll_pwait(). This way, the worker never
+       misses acting on a kick */
+
+    if (!g_initialized_sigmask) {
+      sigemptyset(&g_wakeup_sig_set);
+      sigaddset(&g_wakeup_sig_set, grpc_wakeup_signal);
+      pthread_sigmask(SIG_BLOCK, &g_wakeup_sig_set, &g_orig_sigmask);
+      sigdelset(&g_orig_sigmask, grpc_wakeup_signal);
+      g_initialized_sigmask = true;
+      /* new_mask:       The new thread mask which blocks 'grpc_wakeup_signal'.
+                         This is the mask used at all times *except during
+                         epoll_wait()*"
+         g_orig_sigmask: The thread mask which allows 'grpc_wakeup_signal' and
+                         this is the mask to use *during epoll_wait()*
+
+         The new_mask is set on the worker before it is added to the pollset
+         (i.e before it can be kicked) */
+    }
+
+    push_front_worker(pollset, &worker); /* Add worker to pollset */
+
+    pollset_work_and_unlock(exec_ctx, pollset, &worker, now, deadline,
+                            &g_orig_sigmask, &error);
+    grpc_exec_ctx_flush(exec_ctx);
+
+    gpr_mu_lock(&pollset->po.mu);
+
+    /* Note: There is no need to reset worker.is_kicked to 0 since we are no
+       longer going to use this worker */
+    remove_worker(pollset, &worker);
+  }
+
+  /* If we are the last worker on the pollset (i.e pollset_has_workers() is
+     false at this point) and the pollset is shutting down, we may have to
+     finish the shutdown process by calling finish_shutdown_locked().
+     See pollset_shutdown() for more details.
+
+     Note: Continuing to access pollset here is safe; it is the caller's
+     responsibility to not destroy a pollset when it has outstanding calls to
+     pollset_work() */
+  if (pollset->shutting_down && !pollset_has_workers(pollset) &&
+      !pollset->finish_shutdown_called) {
+    GPR_TIMER_MARK("pollset_work.finish_shutdown_locked", 0);
+    finish_shutdown_locked(exec_ctx, pollset);
+
+    gpr_mu_unlock(&pollset->po.mu);
+    grpc_exec_ctx_flush(exec_ctx);
+    gpr_mu_lock(&pollset->po.mu);
+  }
+
+  if (worker_hdl) *worker_hdl = NULL;
+
+  gpr_tls_set(&g_current_thread_pollset, (intptr_t)0);
+  gpr_tls_set(&g_current_thread_worker, (intptr_t)0);
+
+  GPR_TIMER_END("pollset_work", 0);
+
+  GRPC_LOG_IF_ERROR("pollset_work", GRPC_ERROR_REF(error));
+  return error;
+}
+
+static void add_poll_object(grpc_exec_ctx *exec_ctx, poll_obj *bag,
+                            poll_obj_type bag_type, poll_obj *item,
+                            poll_obj_type item_type) {
+  GPR_TIMER_BEGIN("add_poll_object", 0);
+
+#ifdef PO_DEBUG
+  GPR_ASSERT(item->obj_type == item_type);
+  GPR_ASSERT(bag->obj_type == bag_type);
+#endif
+
+  grpc_error *error = GRPC_ERROR_NONE;
+  polling_island *pi_new = NULL;
+
+  gpr_mu_lock(&bag->mu);
+  gpr_mu_lock(&item->mu);
+
+retry:
+  /*
+   * 1) If item->pi and bag->pi are both non-NULL and equal, do nothing
+   * 2) If item->pi and bag->pi are both NULL, create a new polling island (with
+   *    a refcount of 2) and point item->pi and bag->pi to the new island
+   * 3) If exactly one of item->pi or bag->pi is NULL, update it to point to
+   *    the other's non-NULL pi
+   * 4) Finally if item->pi and bag-pi are non-NULL and not-equal, merge the
+   *    polling islands and update item->pi and bag->pi to point to the new
+   *    island
+   */
+
+  /* Early out if we are trying to add an 'fd' to a 'bag' but the fd is already
+   * orphaned */
+  if (item_type == POLL_OBJ_FD && (FD_FROM_PO(item))->orphaned) {
+    gpr_mu_unlock(&item->mu);
+    gpr_mu_unlock(&bag->mu);
+    return;
+  }
+
+  if (item->pi == bag->pi) {
+    pi_new = item->pi;
+    if (pi_new == NULL) {
+      /* GPR_ASSERT(item->pi == bag->pi == NULL) */
+
+      /* If we are adding an fd to a bag (i.e pollset or pollset_set), then
+       * we need to do some extra work to make TSAN happy */
+      if (item_type == POLL_OBJ_FD) {
+        /* Unlock before creating a new polling island: the polling island will
+           create a workqueue which creates a file descriptor, and holding an fd
+           lock here can eventually cause a loop to appear to TSAN (making it
+           unhappy). We don't think it's a real loop (there's an epoch point
+           where that loop possibility disappears), but the advantages of
+           keeping TSAN happy outweigh any performance advantage we might have
+           by keeping the lock held. */
+        gpr_mu_unlock(&item->mu);
+        pi_new = polling_island_create(exec_ctx, FD_FROM_PO(item), &error);
+        gpr_mu_lock(&item->mu);
+
+        /* Need to reverify any assumptions made between the initial lock and
+           getting to this branch: if they've changed, we need to throw away our
+           work and figure things out again. */
+        if (item->pi != NULL) {
+          GRPC_POLLING_TRACE(
+              "add_poll_object: Raced creating new polling island. pi_new: %p "
+              "(fd: %d, %s: %p)",
+              (void *)pi_new, FD_FROM_PO(item)->fd, poll_obj_string(bag_type),
+              (void *)bag);
+          /* No need to lock 'pi_new' here since this is a new polling island
+             and no one has a reference to it yet */
+          polling_island_remove_all_fds_locked(pi_new, true, &error);
+
+          /* Ref and unref so that the polling island gets deleted during unref
+           */
+          PI_ADD_REF(pi_new, "dance_of_destruction");
+          PI_UNREF(exec_ctx, pi_new, "dance_of_destruction");
+          goto retry;
+        }
+      } else {
+        pi_new = polling_island_create(exec_ctx, NULL, &error);
+      }
+
+      GRPC_POLLING_TRACE(
+          "add_poll_object: Created new polling island. pi_new: %p (%s: %p, "
+          "%s: %p)",
+          (void *)pi_new, poll_obj_string(item_type), (void *)item,
+          poll_obj_string(bag_type), (void *)bag);
+    } else {
+      GRPC_POLLING_TRACE(
+          "add_poll_object: Same polling island. pi: %p (%s, %s)",
+          (void *)pi_new, poll_obj_string(item_type),
+          poll_obj_string(bag_type));
+    }
+  } else if (item->pi == NULL) {
+    /* GPR_ASSERT(bag->pi != NULL) */
+    /* Make pi_new point to latest pi*/
+    pi_new = polling_island_lock(bag->pi);
+
+    if (item_type == POLL_OBJ_FD) {
+      grpc_fd *fd = FD_FROM_PO(item);
+      polling_island_add_fds_locked(pi_new, &fd, 1, true, &error);
+    }
+
+    gpr_mu_unlock(&pi_new->mu);
+    GRPC_POLLING_TRACE(
+        "add_poll_obj: item->pi was NULL. pi_new: %p (item(%s): %p, "
+        "bag(%s): %p)",
+        (void *)pi_new, poll_obj_string(item_type), (void *)item,
+        poll_obj_string(bag_type), (void *)bag);
+  } else if (bag->pi == NULL) {
+    /* GPR_ASSERT(item->pi != NULL) */
+    /* Make pi_new to point to latest pi */
+    pi_new = polling_island_lock(item->pi);
+    gpr_mu_unlock(&pi_new->mu);
+    GRPC_POLLING_TRACE(
+        "add_poll_obj: bag->pi was NULL. pi_new: %p (item(%s): %p, "
+        "bag(%s): %p)",
+        (void *)pi_new, poll_obj_string(item_type), (void *)item,
+        poll_obj_string(bag_type), (void *)bag);
+  } else {
+    pi_new = polling_island_merge(item->pi, bag->pi, &error);
+    GRPC_POLLING_TRACE(
+        "add_poll_obj: polling islands merged. pi_new: %p (item(%s): %p, "
+        "bag(%s): %p)",
+        (void *)pi_new, poll_obj_string(item_type), (void *)item,
+        poll_obj_string(bag_type), (void *)bag);
+  }
+
+  /* At this point, pi_new is the polling island that both item->pi and bag->pi
+     MUST be pointing to */
+
+  if (item->pi != pi_new) {
+    PI_ADD_REF(pi_new, poll_obj_string(item_type));
+    if (item->pi != NULL) {
+      PI_UNREF(exec_ctx, item->pi, poll_obj_string(item_type));
+    }
+    item->pi = pi_new;
+  }
+
+  if (bag->pi != pi_new) {
+    PI_ADD_REF(pi_new, poll_obj_string(bag_type));
+    if (bag->pi != NULL) {
+      PI_UNREF(exec_ctx, bag->pi, poll_obj_string(bag_type));
+    }
+    bag->pi = pi_new;
+  }
+
+  gpr_mu_unlock(&item->mu);
+  gpr_mu_unlock(&bag->mu);
+
+  GRPC_LOG_IF_ERROR("add_poll_object", error);
+  GPR_TIMER_END("add_poll_object", 0);
+}
+
+static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                           grpc_fd *fd) {
+  add_poll_object(exec_ctx, &pollset->po, POLL_OBJ_POLLSET, &fd->po,
+                  POLL_OBJ_FD);
+}
+
+/*******************************************************************************
+ * Pollset-set Definitions
+ */
+
+static grpc_pollset_set *pollset_set_create(void) {
+  grpc_pollset_set *pss = gpr_malloc(sizeof(*pss));
+  gpr_mu_init(&pss->po.mu);
+  pss->po.pi = NULL;
+#ifdef PO_DEBUG
+  pss->po.obj_type = POLL_OBJ_POLLSET_SET;
+#endif
+  return pss;
+}
+
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pss) {
+  gpr_mu_destroy(&pss->po.mu);
+
+  if (pss->po.pi != NULL) {
+    PI_UNREF(exec_ctx, pss->po.pi, "pss_destroy");
+  }
+
+  gpr_free(pss);
+}
+
+static void pollset_set_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {
+  add_poll_object(exec_ctx, &pss->po, POLL_OBJ_POLLSET_SET, &fd->po,
+                  POLL_OBJ_FD);
+}
+
+static void pollset_set_del_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {
+  /* Nothing to do */
+}
+
+static void pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {
+  add_poll_object(exec_ctx, &pss->po, POLL_OBJ_POLLSET_SET, &ps->po,
+                  POLL_OBJ_POLLSET);
+}
+
+static void pollset_set_del_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {
+  /* Nothing to do */
+}
+
+static void pollset_set_add_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {
+  add_poll_object(exec_ctx, &bag->po, POLL_OBJ_POLLSET_SET, &item->po,
+                  POLL_OBJ_POLLSET_SET);
+}
+
+static void pollset_set_del_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {
+  /* Nothing to do */
+}
+
+/*******************************************************************************
+ * Event engine binding
+ */
+
+static void shutdown_engine(void) {
+  fd_global_shutdown();
+  pollset_global_shutdown();
+  polling_island_global_shutdown();
+}
+
+static const grpc_event_engine_vtable vtable = {
+    .pollset_size = sizeof(grpc_pollset),
+
+    .fd_create = fd_create,
+    .fd_wrapped_fd = fd_wrapped_fd,
+    .fd_orphan = fd_orphan,
+    .fd_shutdown = fd_shutdown,
+    .fd_is_shutdown = fd_is_shutdown,
+    .fd_notify_on_read = fd_notify_on_read,
+    .fd_notify_on_write = fd_notify_on_write,
+    .fd_get_read_notifier_pollset = fd_get_read_notifier_pollset,
+    .fd_get_workqueue = fd_get_workqueue,
+
+    .pollset_init = pollset_init,
+    .pollset_shutdown = pollset_shutdown,
+    .pollset_destroy = pollset_destroy,
+    .pollset_work = pollset_work,
+    .pollset_kick = pollset_kick,
+    .pollset_add_fd = pollset_add_fd,
+
+    .pollset_set_create = pollset_set_create,
+    .pollset_set_destroy = pollset_set_destroy,
+    .pollset_set_add_pollset = pollset_set_add_pollset,
+    .pollset_set_del_pollset = pollset_set_del_pollset,
+    .pollset_set_add_pollset_set = pollset_set_add_pollset_set,
+    .pollset_set_del_pollset_set = pollset_set_del_pollset_set,
+    .pollset_set_add_fd = pollset_set_add_fd,
+    .pollset_set_del_fd = pollset_set_del_fd,
+
+    .workqueue_ref = workqueue_ref,
+    .workqueue_unref = workqueue_unref,
+    .workqueue_scheduler = workqueue_scheduler,
+
+    .shutdown_engine = shutdown_engine,
+};
+
+/* It is possible that GLIBC has epoll but the underlying kernel doesn't.
+ * Create a dummy epoll_fd to make sure epoll support is available */
+static bool is_epoll_available() {
+  int fd = epoll_create1(EPOLL_CLOEXEC);
+  if (fd < 0) {
+    gpr_log(
+        GPR_ERROR,
+        "epoll_create1 failed with error: %d. Not using epoll polling engine",
+        fd);
+    return false;
+  }
+  close(fd);
+  return true;
+}
+
+/* This is mainly for testing purposes. Checks to see if environment variable
+ * GRPC_MAX_POLLERS_PER_PI is set and if so, assigns that value to
+ * g_max_pollers_per_pi (any negative value is considered INT_MAX) */
+static void set_max_pollers_per_island() {
+  char *s = gpr_getenv("GRPC_MAX_POLLERS_PER_PI");
+  if (s) {
+    g_max_pollers_per_pi = (int)strtol(s, NULL, 10);
+    if (g_max_pollers_per_pi < 0) {
+      g_max_pollers_per_pi = INT_MAX;
+    }
+  } else {
+    g_max_pollers_per_pi = INT_MAX;
+  }
+
+  gpr_log(GPR_INFO, "Max number of pollers per polling island: %d",
+          g_max_pollers_per_pi);
+}
+
+const grpc_event_engine_vtable *grpc_init_epoll_limited_pollers_linux(
+    bool explicitly_requested) {
+  if (!explicitly_requested) {
+    return NULL;
+  }
+
+  /* If use of signals is disabled, we cannot use epoll engine*/
+  if (is_grpc_wakeup_signal_initialized && grpc_wakeup_signal < 0) {
+    return NULL;
+  }
+
+  if (!grpc_has_wakeup_fd()) {
+    return NULL;
+  }
+
+  if (!is_epoll_available()) {
+    return NULL;
+  }
+
+  if (!is_grpc_wakeup_signal_initialized) {
+    grpc_use_signal(SIGRTMIN + 6);
+  }
+
+  set_max_pollers_per_island();
+
+  fd_global_init();
+
+  if (!GRPC_LOG_IF_ERROR("pollset_global_init", pollset_global_init())) {
+    return NULL;
+  }
+
+  if (!GRPC_LOG_IF_ERROR("polling_island_global_init",
+                         polling_island_global_init())) {
+    return NULL;
+  }
+
+  return &vtable;
+}
+
+#else /* defined(GRPC_LINUX_EPOLL) */
+#if defined(GRPC_POSIX_SOCKET)
+#include "src/core/lib/iomgr/ev_posix.h"
+/* If GRPC_LINUX_EPOLL is not defined, it means epoll is not available. Return
+ * NULL */
+const grpc_event_engine_vtable *grpc_init_epoll_limited_pollers_linux(
+    bool explicitly_requested) {
+  return NULL;
+}
+#endif /* defined(GRPC_POSIX_SOCKET) */
+#endif /* !defined(GRPC_LINUX_EPOLL) */
diff --git a/src/core/lib/iomgr/ev_epoll_limited_pollers_linux.h b/src/core/lib/iomgr/ev_epoll_limited_pollers_linux.h
new file mode 100644
index 0000000000..379e1ded3b
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epoll_limited_pollers_linux.h
@@ -0,0 +1,43 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_EV_EPOLL_LIMITED_POLLERS_LINUX_H
+#define GRPC_CORE_LIB_IOMGR_EV_EPOLL_LIMITED_POLLERS_LINUX_H
+
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/port.h"
+
+const grpc_event_engine_vtable *grpc_init_epoll_limited_pollers_linux(
+    bool explicitly_requested);
+
+#endif /* GRPC_CORE_LIB_IOMGR_EV_EPOLL_LIMITED_POLLERS_LINUX_H */
diff --git a/src/core/lib/iomgr/ev_epoll_thread_pool_linux.c b/src/core/lib/iomgr/ev_epoll_thread_pool_linux.c
new file mode 100644
index 0000000000..bb44321922
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epoll_thread_pool_linux.c
@@ -0,0 +1,1337 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/port.h"
+
+/* This polling engine is only relevant on linux kernels supporting epoll() */
+#ifdef GRPC_LINUX_EPOLL
+
+#include "src/core/lib/iomgr/ev_epoll_thread_pool_linux.h"
+
+#include <assert.h>
+#include <errno.h>
+#include <limits.h>
+#include <poll.h>
+#include <pthread.h>
+#include <string.h>
+#include <sys/epoll.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/cpu.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/thd.h>
+#include <grpc/support/tls.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/iomgr_internal.h"
+#include "src/core/lib/iomgr/lockfree_event.h"
+#include "src/core/lib/iomgr/timer.h"
+#include "src/core/lib/iomgr/wakeup_fd_posix.h"
+#include "src/core/lib/iomgr/workqueue.h"
+#include "src/core/lib/profiling/timers.h"
+#include "src/core/lib/support/block_annotate.h"
+
+/* TODO: sreek - Move this to init.c and initialize this like other tracers. */
+#define GRPC_POLLING_TRACE(fmt, ...)        \
+  if (GRPC_TRACER_ON(grpc_polling_trace)) { \
+    gpr_log(GPR_INFO, (fmt), __VA_ARGS__);  \
+  }
+
+/* The alarm system needs to be able to wakeup 'some poller' sometimes
+ * (specifically when a new alarm needs to be triggered earlier than the next
+ * alarm 'epoch'). This wakeup_fd gives us something to alert on when such a
+ * case occurs. */
+
+struct epoll_set;
+
+#define GRPC_POLLSET_KICK_BROADCAST ((grpc_pollset_worker *)1)
+
+/*******************************************************************************
+ * Fd Declarations
+ */
+struct grpc_fd {
+  gpr_mu mu;
+  struct epoll_set *eps;
+
+  int fd;
+
+  /* The fd is either closed or we relinquished control of it. In either cases,
+     this indicates that the 'fd' on this structure is no longer valid */
+  bool orphaned;
+
+  gpr_atm read_closure;
+  gpr_atm write_closure;
+
+  struct grpc_fd *freelist_next;
+  grpc_closure *on_done_closure;
+
+  grpc_iomgr_object iomgr_object;
+};
+
+static void fd_global_init(void);
+static void fd_global_shutdown(void);
+
+/*******************************************************************************
+ * epoll set Declarations
+ */
+
+#ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
+
+#define EPS_ADD_REF(p, r) eps_add_ref_dbg((p), (r), __FILE__, __LINE__)
+#define EPS_UNREF(exec_ctx, p, r) \
+  eps_unref_dbg((exec_ctx), (p), (r), __FILE__, __LINE__)
+
+#else /* defined(GRPC_WORKQUEUE_REFCOUNT_DEBUG) */
+
+#define EPS_ADD_REF(p, r) eps_add_ref((p))
+#define EPS_UNREF(exec_ctx, p, r) eps_unref((exec_ctx), (p))
+
+#endif /* !defined(GRPC_EPS_REF_COUNT_DEBUG) */
+
+/* This is also used as grpc_workqueue (by directly casting it) */
+typedef struct epoll_set {
+  grpc_closure_scheduler workqueue_scheduler;
+
+  /* Mutex poller should acquire to poll this. This enforces that only one
+   * poller can be polling on epoll_set at any time */
+  gpr_mu mu;
+
+  /* Ref count. Use EPS_ADD_REF() and EPS_UNREF() macros to increment/decrement
+     the refcount. Once the ref count becomes zero, this structure is destroyed
+     which means we should ensure that there is never a scenario where a
+     EPS_ADD_REF() is racing with a EPS_UNREF() that just made the ref_count
+     zero. */
+  gpr_atm ref_count;
+
+  /* Number of threads currently polling on this epoll set*/
+  gpr_atm poller_count;
+  /* Mutex guarding the read end of the workqueue (must be held to pop from
+   * workqueue_items) */
+  gpr_mu workqueue_read_mu;
+  /* Queue of closures to be executed */
+  gpr_mpscq workqueue_items;
+  /* Count of items in workqueue_items */
+  gpr_atm workqueue_item_count;
+  /* Wakeup fd used to wake pollers to check the contents of workqueue_items */
+  grpc_wakeup_fd workqueue_wakeup_fd;
+
+  /* Is the epoll set shutdown */
+  gpr_atm is_shutdown;
+
+  /* The fd of the underlying epoll set */
+  int epoll_fd;
+} epoll_set;
+
+/*******************************************************************************
+ * Pollset Declarations
+ */
+struct grpc_pollset_worker {
+  gpr_cv kick_cv;
+
+  struct grpc_pollset_worker *next;
+  struct grpc_pollset_worker *prev;
+};
+
+struct grpc_pollset {
+  gpr_mu mu;
+  struct epoll_set *eps;
+
+  grpc_pollset_worker root_worker;
+  bool kicked_without_pollers;
+
+  bool shutting_down;          /* Is the pollset shutting down ? */
+  bool finish_shutdown_called; /* Is the 'finish_shutdown_locked()' called ? */
+  grpc_closure *shutdown_done; /* Called after after shutdown is complete */
+};
+
+/*******************************************************************************
+ * Pollset-set Declarations
+ */
+struct grpc_pollset_set {};
+
+/*****************************************************************************
+ * Dedicated polling threads and pollsets - Declarations
+ */
+
+size_t g_num_eps = 1;
+struct epoll_set **g_epoll_sets = NULL;
+gpr_atm g_next_eps;
+size_t g_num_threads_per_eps = 1;
+gpr_thd_id *g_poller_threads = NULL;
+
+/* Used as read-notifier pollsets for fds. We won't be using read notifier
+ * pollsets with this polling engine. So it does not matter what pollset we
+ * return */
+grpc_pollset g_read_notifier;
+
+static void add_fd_to_eps(grpc_fd *fd);
+static bool init_epoll_sets();
+static void shutdown_epoll_sets();
+static void poller_thread_loop(void *arg);
+static void start_poller_threads();
+static void shutdown_poller_threads();
+
+/*******************************************************************************
+ * Common helpers
+ */
+
+static bool append_error(grpc_error **composite, grpc_error *error,
+                         const char *desc) {
+  if (error == GRPC_ERROR_NONE) return true;
+  if (*composite == GRPC_ERROR_NONE) {
+    *composite = GRPC_ERROR_CREATE_FROM_COPIED_STRING(desc);
+  }
+  *composite = grpc_error_add_child(*composite, error);
+  return false;
+}
+
+/*******************************************************************************
+ * epoll set Definitions
+ */
+
+/* The wakeup fd that is used to wake up all threads in an epoll_set informing
+   that the epoll set is shutdown.  This wakeup fd initialized to be readable
+   and MUST NOT be consumed i.e the threads that woke up MUST NOT call
+   grpc_wakeup_fd_consume_wakeup() */
+static grpc_wakeup_fd epoll_set_wakeup_fd;
+
+/* The epoll set being polled right now.
+   See comments in workqueue_maybe_wakeup for why this is tracked. */
+static __thread epoll_set *g_current_thread_epoll_set;
+
+/* Forward declaration */
+static void epoll_set_delete(epoll_set *eps);
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                              grpc_error *error);
+
+#ifdef GRPC_TSAN
+/* Currently TSAN may incorrectly flag data races between epoll_ctl and
+   epoll_wait for any grpc_fd structs that are added to the epoll set via
+   epoll_ctl and are returned (within a very short window) via epoll_wait().
+
+   To work-around this race, we establish a happens-before relation between
+   the code just-before epoll_ctl() and the code after epoll_wait() by using
+   this atomic */
+gpr_atm g_epoll_sync;
+#endif /* defined(GRPC_TSAN) */
+
+static const grpc_closure_scheduler_vtable workqueue_scheduler_vtable = {
+    workqueue_enqueue, workqueue_enqueue, "workqueue"};
+
+static void eps_add_ref(epoll_set *eps);
+static void eps_unref(grpc_exec_ctx *exec_ctx, epoll_set *eps);
+
+#ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
+static void eps_add_ref_dbg(epoll_set *eps, const char *reason,
+                            const char *file, int line) {
+  long old_cnt = gpr_atm_acq_load(&eps->ref_count);
+  eps_add_ref(eps);
+  gpr_log(GPR_DEBUG, "Add ref eps: %p, old: %ld -> new:%ld (%s) - (%s, %d)",
+          (void *)eps, old_cnt, old_cnt + 1, reason, file, line);
+}
+
+static void eps_unref_dbg(grpc_exec_ctx *exec_ctx, epoll_set *eps,
+                          const char *reason, const char *file, int line) {
+  long old_cnt = gpr_atm_acq_load(&eps->ref_count);
+  eps_unref(exec_ctx, eps);
+  gpr_log(GPR_DEBUG, "Unref eps: %p, old:%ld -> new:%ld (%s) - (%s, %d)",
+          (void *)eps, old_cnt, (old_cnt - 1), reason, file, line);
+}
+
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue,
+                                     const char *file, int line,
+                                     const char *reason) {
+  if (workqueue != NULL) {
+    eps_add_ref_dbg((epoll_set *)workqueue, reason, file, line);
+  }
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
+                            const char *file, int line, const char *reason) {
+  if (workqueue != NULL) {
+    eps_unref_dbg(exec_ctx, (epoll_set *)workqueue, reason, file, line);
+  }
+}
+#else
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue) {
+  if (workqueue != NULL) {
+    eps_add_ref((epoll_set *)workqueue);
+  }
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx,
+                            grpc_workqueue *workqueue) {
+  if (workqueue != NULL) {
+    eps_unref(exec_ctx, (epoll_set *)workqueue);
+  }
+}
+#endif
+
+static void eps_add_ref(epoll_set *eps) {
+  gpr_atm_no_barrier_fetch_add(&eps->ref_count, 1);
+}
+
+static void eps_unref(grpc_exec_ctx *exec_ctx, epoll_set *eps) {
+  /* If ref count went to zero, delete the epoll set. This deletion is
+     not done under a lock since once the ref count goes to zero, we are
+     guaranteed that no one else holds a reference to the epoll set (and
+     that there is no racing eps_add_ref() call either).*/
+  if (1 == gpr_atm_full_fetch_add(&eps->ref_count, -1)) {
+    epoll_set_delete(eps);
+  }
+}
+
+static void epoll_set_add_fd_locked(epoll_set *eps, grpc_fd *fd,
+                                    grpc_error **error) {
+  int err;
+  struct epoll_event ev;
+  char *err_msg;
+  const char *err_desc = "epoll_set_add_fd_locked";
+
+#ifdef GRPC_TSAN
+  /* See the definition of g_epoll_sync for more context */
+  gpr_atm_rel_store(&g_epoll_sync, (gpr_atm)0);
+#endif /* defined(GRPC_TSAN) */
+
+  ev.events = (uint32_t)(EPOLLIN | EPOLLOUT | EPOLLET);
+  ev.data.ptr = fd;
+  err = epoll_ctl(eps->epoll_fd, EPOLL_CTL_ADD, fd->fd, &ev);
+  if (err < 0 && errno != EEXIST) {
+    gpr_asprintf(
+        &err_msg,
+        "epoll_ctl (epoll_fd: %d) add fd: %d failed with error: %d (%s)",
+        eps->epoll_fd, fd->fd, errno, strerror(errno));
+    append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+    gpr_free(err_msg);
+  }
+}
+
+static void epoll_set_add_wakeup_fd_locked(epoll_set *eps,
+                                           grpc_wakeup_fd *wakeup_fd,
+                                           grpc_error **error) {
+  struct epoll_event ev;
+  int err;
+  char *err_msg;
+  const char *err_desc = "epoll_set_add_wakeup_fd";
+
+  ev.events = (uint32_t)(EPOLLIN | EPOLLET);
+  ev.data.ptr = wakeup_fd;
+  err = epoll_ctl(eps->epoll_fd, EPOLL_CTL_ADD,
+                  GRPC_WAKEUP_FD_GET_READ_FD(wakeup_fd), &ev);
+  if (err < 0 && errno != EEXIST) {
+    gpr_asprintf(&err_msg,
+                 "epoll_ctl (epoll_fd: %d) add wakeup fd: %d failed with "
+                 "error: %d (%s)",
+                 eps->epoll_fd, GRPC_WAKEUP_FD_GET_READ_FD(wakeup_fd), errno,
+                 strerror(errno));
+    append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+    gpr_free(err_msg);
+  }
+}
+
+static void epoll_set_remove_fd(epoll_set *eps, grpc_fd *fd, bool is_fd_closed,
+                                grpc_error **error) {
+  int err;
+  char *err_msg;
+  const char *err_desc = "epoll_set_remove_fd";
+
+  /* If fd is already closed, then it would have been automatically been removed
+     from the epoll set */
+  if (!is_fd_closed) {
+    err = epoll_ctl(eps->epoll_fd, EPOLL_CTL_DEL, fd->fd, NULL);
+    if (err < 0 && errno != ENOENT) {
+      gpr_asprintf(
+          &err_msg,
+          "epoll_ctl (epoll_fd: %d) del fd: %d failed with error: %d (%s)",
+          eps->epoll_fd, fd->fd, errno, strerror(errno));
+      append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+      gpr_free(err_msg);
+    }
+  }
+}
+
+/* Might return NULL in case of an error */
+static epoll_set *epoll_set_create(grpc_error **error) {
+  epoll_set *eps = NULL;
+  const char *err_desc = "epoll_set_create";
+
+  *error = GRPC_ERROR_NONE;
+
+  eps = gpr_malloc(sizeof(*eps));
+  eps->workqueue_scheduler.vtable = &workqueue_scheduler_vtable;
+  eps->epoll_fd = -1;
+
+  gpr_mu_init(&eps->mu);
+  gpr_mu_init(&eps->workqueue_read_mu);
+  gpr_mpscq_init(&eps->workqueue_items);
+  gpr_atm_rel_store(&eps->workqueue_item_count, 0);
+
+  gpr_atm_rel_store(&eps->ref_count, 0);
+  gpr_atm_rel_store(&eps->poller_count, 0);
+
+  gpr_atm_rel_store(&eps->is_shutdown, false);
+
+  if (!append_error(error, grpc_wakeup_fd_init(&eps->workqueue_wakeup_fd),
+                    err_desc)) {
+    goto done;
+  }
+
+  eps->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
+
+  if (eps->epoll_fd < 0) {
+    append_error(error, GRPC_OS_ERROR(errno, "epoll_create1"), err_desc);
+    goto done;
+  }
+
+  epoll_set_add_wakeup_fd_locked(eps, &eps->workqueue_wakeup_fd, error);
+
+done:
+  if (*error != GRPC_ERROR_NONE) {
+    epoll_set_delete(eps);
+    eps = NULL;
+  }
+  return eps;
+}
+
+static void epoll_set_delete(epoll_set *eps) {
+  if (eps->epoll_fd >= 0) {
+    close(eps->epoll_fd);
+  }
+
+  GPR_ASSERT(gpr_atm_no_barrier_load(&eps->workqueue_item_count) == 0);
+  gpr_mu_destroy(&eps->mu);
+  gpr_mu_destroy(&eps->workqueue_read_mu);
+  gpr_mpscq_destroy(&eps->workqueue_items);
+  grpc_wakeup_fd_destroy(&eps->workqueue_wakeup_fd);
+
+  gpr_free(eps);
+}
+
+static void workqueue_maybe_wakeup(epoll_set *eps) {
+  /* If this thread is the current poller, then it may be that it's about to
+     decrement the current poller count, so we need to look past this thread */
+  bool is_current_poller = (g_current_thread_epoll_set == eps);
+  gpr_atm min_current_pollers_for_wakeup = is_current_poller ? 1 : 0;
+  gpr_atm current_pollers = gpr_atm_no_barrier_load(&eps->poller_count);
+  /* Only issue a wakeup if it's likely that some poller could come in and take
+     it right now. Note that since we do an anticipatory mpscq_pop every poll
+     loop, it's ok if we miss the wakeup here, as we'll get the work item when
+     the next poller enters anyway. */
+  if (current_pollers > min_current_pollers_for_wakeup) {
+    GRPC_LOG_IF_ERROR("workqueue_wakeup_fd",
+                      grpc_wakeup_fd_wakeup(&eps->workqueue_wakeup_fd));
+  }
+}
+
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                              grpc_error *error) {
+  GPR_TIMER_BEGIN("workqueue.enqueue", 0);
+  grpc_workqueue *workqueue = (grpc_workqueue *)closure->scheduler;
+  /* take a ref to the workqueue: otherwise it can happen that whatever events
+   * this kicks off ends up destroying the workqueue before this function
+   * completes */
+  GRPC_WORKQUEUE_REF(workqueue, "enqueue");
+  epoll_set *eps = (epoll_set *)workqueue;
+  gpr_atm last = gpr_atm_no_barrier_fetch_add(&eps->workqueue_item_count, 1);
+  closure->error_data.error = error;
+  gpr_mpscq_push(&eps->workqueue_items, &closure->next_data.atm_next);
+  if (last == 0) {
+    workqueue_maybe_wakeup(eps);
+  }
+
+  GRPC_WORKQUEUE_UNREF(exec_ctx, workqueue, "enqueue");
+  GPR_TIMER_END("workqueue.enqueue", 0);
+}
+
+static grpc_closure_scheduler *workqueue_scheduler(grpc_workqueue *workqueue) {
+  epoll_set *eps = (epoll_set *)workqueue;
+  return workqueue == NULL ? grpc_schedule_on_exec_ctx
+                           : &eps->workqueue_scheduler;
+}
+
+static grpc_error *epoll_set_global_init() {
+  grpc_error *error = GRPC_ERROR_NONE;
+
+  error = grpc_wakeup_fd_init(&epoll_set_wakeup_fd);
+  if (error == GRPC_ERROR_NONE) {
+    error = grpc_wakeup_fd_wakeup(&epoll_set_wakeup_fd);
+  }
+
+  return error;
+}
+
+static void epoll_set_global_shutdown() {
+  grpc_wakeup_fd_destroy(&epoll_set_wakeup_fd);
+}
+
+/*******************************************************************************
+ * Fd Definitions
+ */
+
+/* We need to keep a freelist not because of any concerns of malloc performance
+ * but instead so that implementations with multiple threads in (for example)
+ * epoll_wait deal with the race between pollset removal and incoming poll
+ * notifications.
+ *
+ * The problem is that the poller ultimately holds a reference to this
+ * object, so it is very difficult to know when is safe to free it, at least
+ * without some expensive synchronization.
+ *
+ * If we keep the object freelisted, in the worst case losing this race just
+ * becomes a spurious read notification on a reused fd.
+ */
+
+static grpc_fd *fd_freelist = NULL;
+static gpr_mu fd_freelist_mu;
+
+static grpc_fd *get_fd_from_freelist() {
+  grpc_fd *new_fd = NULL;
+
+  gpr_mu_lock(&fd_freelist_mu);
+  if (fd_freelist != NULL) {
+    new_fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+  }
+  gpr_mu_unlock(&fd_freelist_mu);
+  return new_fd;
+}
+
+static void add_fd_to_freelist(grpc_fd *fd) {
+  gpr_mu_lock(&fd_freelist_mu);
+  fd->freelist_next = fd_freelist;
+  fd_freelist = fd;
+  grpc_iomgr_unregister_object(&fd->iomgr_object);
+
+  grpc_lfev_destroy(&fd->read_closure);
+  grpc_lfev_destroy(&fd->write_closure);
+
+  gpr_mu_unlock(&fd_freelist_mu);
+}
+
+static void fd_global_init(void) { gpr_mu_init(&fd_freelist_mu); }
+
+static void fd_global_shutdown(void) {
+  gpr_mu_lock(&fd_freelist_mu);
+  gpr_mu_unlock(&fd_freelist_mu);
+  while (fd_freelist != NULL) {
+    grpc_fd *fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+    gpr_mu_destroy(&fd->mu);
+    gpr_free(fd);
+  }
+  gpr_mu_destroy(&fd_freelist_mu);
+}
+
+static grpc_fd *fd_create(int fd, const char *name) {
+  grpc_fd *new_fd = get_fd_from_freelist();
+  if (new_fd == NULL) {
+    new_fd = gpr_malloc(sizeof(grpc_fd));
+    gpr_mu_init(&new_fd->mu);
+  }
+
+  /* Note: It is not really needed to get the new_fd->mu lock here. If this
+   * is a newly created fd (or an fd we got from the freelist), no one else
+   * would be holding a lock to it anyway. */
+  gpr_mu_lock(&new_fd->mu);
+  new_fd->eps = NULL;
+
+  new_fd->fd = fd;
+  new_fd->orphaned = false;
+  grpc_lfev_init(&new_fd->read_closure);
+  grpc_lfev_init(&new_fd->write_closure);
+
+  new_fd->freelist_next = NULL;
+  new_fd->on_done_closure = NULL;
+
+  gpr_mu_unlock(&new_fd->mu);
+
+  char *fd_name;
+  gpr_asprintf(&fd_name, "%s fd=%d", name, fd);
+  grpc_iomgr_register_object(&new_fd->iomgr_object, fd_name);
+  gpr_log(GPR_DEBUG, "FD %d %p create %s", fd, (void *)new_fd, fd_name);
+  gpr_free(fd_name);
+
+  /* Associate the fd with one of the eps */
+  add_fd_to_eps(new_fd);
+  return new_fd;
+}
+
+static int fd_wrapped_fd(grpc_fd *fd) {
+  int ret_fd = -1;
+  gpr_mu_lock(&fd->mu);
+  if (!fd->orphaned) {
+    ret_fd = fd->fd;
+  }
+  gpr_mu_unlock(&fd->mu);
+
+  return ret_fd;
+}
+
+static void fd_orphan(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                      grpc_closure *on_done, int *release_fd,
+                      const char *reason) {
+  bool is_fd_closed = false;
+  grpc_error *error = GRPC_ERROR_NONE;
+  epoll_set *unref_eps = NULL;
+
+  gpr_mu_lock(&fd->mu);
+  fd->on_done_closure = on_done;
+
+  /* If release_fd is not NULL, we should be relinquishing control of the file
+     descriptor fd->fd (but we still own the grpc_fd structure). */
+  if (release_fd != NULL) {
+    *release_fd = fd->fd;
+  } else {
+    close(fd->fd);
+    is_fd_closed = true;
+  }
+
+  fd->orphaned = true;
+
+  /* Remove the fd from the epoll set */
+  if (fd->eps != NULL) {
+    epoll_set_remove_fd(fd->eps, fd, is_fd_closed, &error);
+    unref_eps = fd->eps;
+    fd->eps = NULL;
+  }
+
+  grpc_closure_sched(exec_ctx, fd->on_done_closure, GRPC_ERROR_REF(error));
+
+  gpr_mu_unlock(&fd->mu);
+
+  /* We are done with this fd. Release it (i.e add back to freelist) */
+  add_fd_to_freelist(fd);
+
+  if (unref_eps != NULL) {
+    /* Unref stale epoll set here, outside the fd lock above.
+       The epoll set owns a workqueue which owns an fd, and unreffing
+       inside the lock can cause an eventual lock loop that makes TSAN very
+       unhappy. */
+    EPS_UNREF(exec_ctx, unref_eps, "fd_orphan");
+  }
+  GRPC_LOG_IF_ERROR("fd_orphan", GRPC_ERROR_REF(error));
+  GRPC_ERROR_UNREF(error);
+}
+
+/* This polling engine doesn't really need the read notifier functionality. So
+ * it just returns a dummy read notifier pollset */
+static grpc_pollset *fd_get_read_notifier_pollset(grpc_exec_ctx *exec_ctx,
+                                                  grpc_fd *fd) {
+  return &g_read_notifier;
+}
+
+static bool fd_is_shutdown(grpc_fd *fd) {
+  return grpc_lfev_is_shutdown(&fd->read_closure);
+}
+
+/* Might be called multiple times */
+static void fd_shutdown(grpc_exec_ctx *exec_ctx, grpc_fd *fd, grpc_error *why) {
+  if (grpc_lfev_set_shutdown(exec_ctx, &fd->read_closure,
+                             GRPC_ERROR_REF(why))) {
+    shutdown(fd->fd, SHUT_RDWR);
+    grpc_lfev_set_shutdown(exec_ctx, &fd->write_closure, GRPC_ERROR_REF(why));
+  }
+  GRPC_ERROR_UNREF(why);
+}
+
+static void fd_notify_on_read(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                              grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->read_closure, closure);
+}
+
+static void fd_notify_on_write(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                               grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->write_closure, closure);
+}
+
+static grpc_workqueue *fd_get_workqueue(grpc_fd *fd) { return NULL; }
+
+/*******************************************************************************
+ * Pollset Definitions
+ */
+/* TODO: sreek - Not needed anymore */
+GPR_TLS_DECL(g_current_thread_pollset);
+GPR_TLS_DECL(g_current_thread_worker);
+
+static void pollset_worker_init(grpc_pollset_worker *worker) {
+  worker->next = worker->prev = NULL;
+  gpr_cv_init(&worker->kick_cv);
+}
+
+/* Global state management */
+static grpc_error *pollset_global_init(void) {
+  gpr_tls_init(&g_current_thread_pollset);
+  gpr_tls_init(&g_current_thread_worker);
+  return GRPC_ERROR_NONE;
+}
+
+static void pollset_global_shutdown(void) {
+  gpr_tls_destroy(&g_current_thread_pollset);
+  gpr_tls_destroy(&g_current_thread_worker);
+}
+
+static grpc_error *pollset_worker_kick(grpc_pollset_worker *worker) {
+  gpr_cv_signal(&worker->kick_cv);
+  return GRPC_ERROR_NONE;
+}
+
+/* Return 1 if the pollset has active threads in pollset_work (pollset must
+ * be locked) */
+static int pollset_has_workers(grpc_pollset *p) {
+  return p->root_worker.next != &p->root_worker;
+}
+
+static void remove_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
+  worker->prev->next = worker->next;
+  worker->next->prev = worker->prev;
+}
+
+static grpc_pollset_worker *pop_front_worker(grpc_pollset *p) {
+  if (pollset_has_workers(p)) {
+    grpc_pollset_worker *w = p->root_worker.next;
+    remove_worker(p, w);
+    return w;
+  } else {
+    return NULL;
+  }
+}
+
+static void push_back_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
+  worker->next = &p->root_worker;
+  worker->prev = worker->next->prev;
+  worker->prev->next = worker->next->prev = worker;
+}
+
+static void push_front_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
+  worker->prev = &p->root_worker;
+  worker->next = worker->prev->next;
+  worker->prev->next = worker->next->prev = worker;
+}
+
+/* p->mu must be held before calling this function */
+static grpc_error *pollset_kick(grpc_pollset *p,
+                                grpc_pollset_worker *specific_worker) {
+  GPR_TIMER_BEGIN("pollset_kick", 0);
+  grpc_error *error = GRPC_ERROR_NONE;
+  const char *err_desc = "Kick Failure";
+  grpc_pollset_worker *worker = specific_worker;
+  if (worker != NULL) {
+    if (worker == GRPC_POLLSET_KICK_BROADCAST) {
+      if (pollset_has_workers(p)) {
+        GPR_TIMER_BEGIN("pollset_kick.broadcast", 0);
+        for (worker = p->root_worker.next; worker != &p->root_worker;
+             worker = worker->next) {
+          if (gpr_tls_get(&g_current_thread_worker) != (intptr_t)worker) {
+            append_error(&error, pollset_worker_kick(worker), err_desc);
+          }
+        }
+        GPR_TIMER_END("pollset_kick.broadcast", 0);
+      } else {
+        p->kicked_without_pollers = true;
+      }
+    } else {
+      GPR_TIMER_MARK("kicked_specifically", 0);
+      if (gpr_tls_get(&g_current_thread_worker) != (intptr_t)worker) {
+        append_error(&error, pollset_worker_kick(worker), err_desc);
+      }
+    }
+  } else if (gpr_tls_get(&g_current_thread_pollset) != (intptr_t)p) {
+    /* Since worker == NULL, it means that we can kick "any" worker on this
+       pollset 'p'. If 'p' happens to be the same pollset this thread is
+       currently polling (i.e in pollset_work() function), then there is no need
+       to kick any other worker since the current thread can just absorb the
+       kick. This is the reason why we enter this case only when
+       g_current_thread_pollset is != p */
+
+    GPR_TIMER_MARK("kick_anonymous", 0);
+    worker = pop_front_worker(p);
+    if (worker != NULL) {
+      GPR_TIMER_MARK("finally_kick", 0);
+      push_back_worker(p, worker);
+      append_error(&error, pollset_worker_kick(worker), err_desc);
+    } else {
+      GPR_TIMER_MARK("kicked_no_pollers", 0);
+      p->kicked_without_pollers = true;
+    }
+  }
+
+  GPR_TIMER_END("pollset_kick", 0);
+  GRPC_LOG_IF_ERROR("pollset_kick", GRPC_ERROR_REF(error));
+  return error;
+}
+
+static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
+  gpr_mu_init(&pollset->mu);
+  *mu = &pollset->mu;
+  pollset->eps = NULL;
+
+  pollset->root_worker.next = pollset->root_worker.prev = &pollset->root_worker;
+  pollset->kicked_without_pollers = false;
+
+  pollset->shutting_down = false;
+  pollset->finish_shutdown_called = false;
+  pollset->shutdown_done = NULL;
+}
+
+static void fd_become_readable(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
+  grpc_lfev_set_ready(exec_ctx, &fd->read_closure);
+}
+
+static void fd_become_writable(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
+  grpc_lfev_set_ready(exec_ctx, &fd->write_closure);
+}
+
+static void pollset_release_epoll_set(grpc_exec_ctx *exec_ctx, grpc_pollset *ps,
+                                      char *reason) {
+  if (ps->eps != NULL) {
+    EPS_UNREF(exec_ctx, ps->eps, reason);
+  }
+  ps->eps = NULL;
+}
+
+static void finish_shutdown_locked(grpc_exec_ctx *exec_ctx,
+                                   grpc_pollset *pollset) {
+  /* The pollset cannot have any workers if we are at this stage */
+  GPR_ASSERT(!pollset_has_workers(pollset));
+
+  pollset->finish_shutdown_called = true;
+
+  /* Release the ref and set pollset->eps to NULL */
+  pollset_release_epoll_set(exec_ctx, pollset, "ps_shutdown");
+  grpc_closure_sched(exec_ctx, pollset->shutdown_done, GRPC_ERROR_NONE);
+}
+
+/* pollset->mu lock must be held by the caller before calling this */
+static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                             grpc_closure *closure) {
+  GPR_TIMER_BEGIN("pollset_shutdown", 0);
+  GPR_ASSERT(!pollset->shutting_down);
+  pollset->shutting_down = true;
+  pollset->shutdown_done = closure;
+  pollset_kick(pollset, GRPC_POLLSET_KICK_BROADCAST);
+
+  /* If the pollset has any workers, we cannot call finish_shutdown_locked()
+     because it would release the underlying epoll set. In such a case, we
+     let the last worker call finish_shutdown_locked() from pollset_work() */
+  if (!pollset_has_workers(pollset)) {
+    GPR_ASSERT(!pollset->finish_shutdown_called);
+    GPR_TIMER_MARK("pollset_shutdown.finish_shutdown_locked", 0);
+    finish_shutdown_locked(exec_ctx, pollset);
+  }
+  GPR_TIMER_END("pollset_shutdown", 0);
+}
+
+/* pollset_shutdown is guaranteed to be called before pollset_destroy. So other
+ * than destroying the mutexes, there is nothing special that needs to be done
+ * here */
+static void pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
+  GPR_ASSERT(!pollset_has_workers(pollset));
+  gpr_mu_destroy(&pollset->mu);
+}
+
+static bool maybe_do_workqueue_work(grpc_exec_ctx *exec_ctx, epoll_set *eps) {
+  if (gpr_mu_trylock(&eps->workqueue_read_mu)) {
+    gpr_mpscq_node *n = gpr_mpscq_pop(&eps->workqueue_items);
+    gpr_mu_unlock(&eps->workqueue_read_mu);
+    if (n != NULL) {
+      if (gpr_atm_full_fetch_add(&eps->workqueue_item_count, -1) > 1) {
+        workqueue_maybe_wakeup(eps);
+      }
+      grpc_closure *c = (grpc_closure *)n;
+      grpc_error *error = c->error_data.error;
+#ifndef NDEBUG
+      c->scheduled = false;
+#endif
+      c->cb(exec_ctx, c->cb_arg, error);
+      GRPC_ERROR_UNREF(error);
+      return true;
+    } else if (gpr_atm_no_barrier_load(&eps->workqueue_item_count) > 0) {
+      /* n == NULL might mean there's work but it's not available to be popped
+       * yet - try to ensure another workqueue wakes up to check shortly if so
+       */
+      workqueue_maybe_wakeup(eps);
+    }
+  }
+  return false;
+}
+
+/* Blocking call */
+static void acquire_epoll_lease(epoll_set *eps) {
+  if (g_num_threads_per_eps > 1) {
+    gpr_mu_lock(&eps->mu);
+  }
+}
+
+static void release_epoll_lease(epoll_set *eps) {
+  if (g_num_threads_per_eps > 1) {
+    gpr_mu_unlock(&eps->mu);
+  }
+}
+
+#define GRPC_EPOLL_MAX_EVENTS 100
+static void do_epoll_wait(grpc_exec_ctx *exec_ctx, int epoll_fd, epoll_set *eps,
+                          grpc_error **error) {
+  struct epoll_event ep_ev[GRPC_EPOLL_MAX_EVENTS];
+  int ep_rv;
+  char *err_msg;
+  const char *err_desc = "do_epoll_wait";
+
+  int timeout_ms = -1;
+
+  GRPC_SCHEDULING_START_BLOCKING_REGION;
+  acquire_epoll_lease(eps);
+  ep_rv = epoll_wait(epoll_fd, ep_ev, GRPC_EPOLL_MAX_EVENTS, timeout_ms);
+  release_epoll_lease(eps);
+  GRPC_SCHEDULING_END_BLOCKING_REGION;
+
+  if (ep_rv < 0) {
+    gpr_asprintf(&err_msg,
+                 "epoll_wait() epoll fd: %d failed with error: %d (%s)",
+                 epoll_fd, errno, strerror(errno));
+    append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
+  }
+
+#ifdef GRPC_TSAN
+  /* See the definition of g_poll_sync for more details */
+  gpr_atm_acq_load(&g_epoll_sync);
+#endif /* defined(GRPC_TSAN) */
+
+  for (int i = 0; i < ep_rv; ++i) {
+    void *data_ptr = ep_ev[i].data.ptr;
+    if (data_ptr == &eps->workqueue_wakeup_fd) {
+      append_error(error,
+                   grpc_wakeup_fd_consume_wakeup(&eps->workqueue_wakeup_fd),
+                   err_desc);
+      maybe_do_workqueue_work(exec_ctx, eps);
+    } else if (data_ptr == &epoll_set_wakeup_fd) {
+      gpr_atm_rel_store(&eps->is_shutdown, 1);
+      gpr_log(GPR_INFO, "pollset poller: shutdown set");
+    } else {
+      grpc_fd *fd = data_ptr;
+      int cancel = ep_ev[i].events & (EPOLLERR | EPOLLHUP);
+      int read_ev = ep_ev[i].events & (EPOLLIN | EPOLLPRI);
+      int write_ev = ep_ev[i].events & EPOLLOUT;
+      if (read_ev || cancel) {
+        fd_become_readable(exec_ctx, fd);
+      }
+      if (write_ev || cancel) {
+        fd_become_writable(exec_ctx, fd);
+      }
+    }
+  }
+}
+
+static void epoll_set_work(grpc_exec_ctx *exec_ctx, epoll_set *eps,
+                           grpc_error **error) {
+  int epoll_fd = -1;
+  GPR_TIMER_BEGIN("epoll_set_work", 0);
+
+  /* Since epoll_fd is immutable, it is safe to read it without a lock on the
+     epoll set. */
+  epoll_fd = eps->epoll_fd;
+
+  /* If we get some workqueue work to do, it might end up completing an item on
+     the completion queue, so there's no need to poll... so we skip that and
+     redo the complete loop to verify */
+  if (!maybe_do_workqueue_work(exec_ctx, eps)) {
+    gpr_atm_no_barrier_fetch_add(&eps->poller_count, 1);
+    g_current_thread_epoll_set = eps;
+
+    do_epoll_wait(exec_ctx, epoll_fd, eps, error);
+
+    g_current_thread_epoll_set = NULL;
+    gpr_atm_no_barrier_fetch_add(&eps->poller_count, -1);
+  }
+
+  GPR_TIMER_END("epoll_set_work", 0);
+}
+
+/* pollset->mu lock must be held by the caller before calling this.
+   The function pollset_work() may temporarily release the lock (pollset->mu)
+   during the course of its execution but it will always re-acquire the lock and
+   ensure that it is held by the time the function returns */
+static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                                grpc_pollset_worker **worker_hdl,
+                                gpr_timespec now, gpr_timespec deadline) {
+  GPR_TIMER_BEGIN("pollset_work", 0);
+  grpc_error *error = GRPC_ERROR_NONE;
+
+  grpc_pollset_worker worker;
+  pollset_worker_init(&worker);
+
+  if (worker_hdl) *worker_hdl = &worker;
+
+  gpr_tls_set(&g_current_thread_pollset, (intptr_t)pollset);
+  gpr_tls_set(&g_current_thread_worker, (intptr_t)&worker);
+
+  if (pollset->kicked_without_pollers) {
+    /* If the pollset was kicked without pollers, pretend that the current
+       worker got the kick and skip polling. A kick indicates that there is some
+       work that needs attention like an event on the completion queue or an
+       alarm */
+    GPR_TIMER_MARK("pollset_work.kicked_without_pollers", 0);
+    pollset->kicked_without_pollers = 0;
+  } else if (!pollset->shutting_down) {
+    push_front_worker(pollset, &worker);
+
+    gpr_cv_wait(&worker.kick_cv, &pollset->mu,
+                gpr_convert_clock_type(deadline, GPR_CLOCK_REALTIME));
+    /* pollset->mu locked here */
+
+    remove_worker(pollset, &worker);
+  }
+
+  /* If we are the last worker on the pollset (i.e pollset_has_workers() is
+     false at this point) and the pollset is shutting down, we may have to
+     finish the shutdown process by calling finish_shutdown_locked().
+     See pollset_shutdown() for more details.
+
+     Note: Continuing to access pollset here is safe; it is the caller's
+     responsibility to not destroy a pollset when it has outstanding calls to
+     pollset_work() */
+  if (pollset->shutting_down && !pollset_has_workers(pollset) &&
+      !pollset->finish_shutdown_called) {
+    GPR_TIMER_MARK("pollset_work.finish_shutdown_locked", 0);
+    finish_shutdown_locked(exec_ctx, pollset);
+
+    gpr_mu_unlock(&pollset->mu);
+    grpc_exec_ctx_flush(exec_ctx);
+    gpr_mu_lock(&pollset->mu);
+  }
+
+  if (worker_hdl) *worker_hdl = NULL;
+
+  gpr_tls_set(&g_current_thread_pollset, (intptr_t)0);
+  gpr_tls_set(&g_current_thread_worker, (intptr_t)0);
+
+  GPR_TIMER_END("pollset_work", 0);
+
+  GRPC_LOG_IF_ERROR("pollset_work", GRPC_ERROR_REF(error));
+  return error;
+}
+
+static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                           grpc_fd *fd) {
+  /* Nothing to do */
+}
+
+/*******************************************************************************
+ * Pollset-set Definitions
+ */
+grpc_pollset_set g_dummy_pollset_set;
+static grpc_pollset_set *pollset_set_create(void) {
+  return &g_dummy_pollset_set;
+}
+
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pss) {
+  /* Nothing to do */
+}
+
+static void pollset_set_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {
+  /* Nothing to do */
+}
+
+static void pollset_set_del_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {
+  /* Nothing to do */
+}
+
+static void pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {
+  /* Nothing to do */
+}
+
+static void pollset_set_del_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {
+  /* Nothing to do */
+}
+
+static void pollset_set_add_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {
+  /* Nothing to do */
+}
+
+static void pollset_set_del_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {
+  /* Nothing to do */
+}
+
+/*******************************************************************************
+ * Event engine binding
+ */
+
+static void shutdown_engine(void) {
+  shutdown_poller_threads();
+  shutdown_epoll_sets();
+  fd_global_shutdown();
+  pollset_global_shutdown();
+  epoll_set_global_shutdown();
+  gpr_log(GPR_INFO, "ev-epoll-threadpool engine shutdown complete");
+}
+
+static const grpc_event_engine_vtable vtable = {
+    .pollset_size = sizeof(grpc_pollset),
+
+    .fd_create = fd_create,
+    .fd_wrapped_fd = fd_wrapped_fd,
+    .fd_orphan = fd_orphan,
+    .fd_shutdown = fd_shutdown,
+    .fd_is_shutdown = fd_is_shutdown,
+    .fd_notify_on_read = fd_notify_on_read,
+    .fd_notify_on_write = fd_notify_on_write,
+    .fd_get_read_notifier_pollset = fd_get_read_notifier_pollset,
+    .fd_get_workqueue = fd_get_workqueue,
+
+    .pollset_init = pollset_init,
+    .pollset_shutdown = pollset_shutdown,
+    .pollset_destroy = pollset_destroy,
+    .pollset_work = pollset_work,
+    .pollset_kick = pollset_kick,
+    .pollset_add_fd = pollset_add_fd,
+
+    .pollset_set_create = pollset_set_create,
+    .pollset_set_destroy = pollset_set_destroy,
+    .pollset_set_add_pollset = pollset_set_add_pollset,
+    .pollset_set_del_pollset = pollset_set_del_pollset,
+    .pollset_set_add_pollset_set = pollset_set_add_pollset_set,
+    .pollset_set_del_pollset_set = pollset_set_del_pollset_set,
+    .pollset_set_add_fd = pollset_set_add_fd,
+    .pollset_set_del_fd = pollset_set_del_fd,
+
+    .workqueue_ref = workqueue_ref,
+    .workqueue_unref = workqueue_unref,
+    .workqueue_scheduler = workqueue_scheduler,
+
+    .shutdown_engine = shutdown_engine,
+};
+
+/*****************************************************************************
+ * Dedicated polling threads and pollsets - Definitions
+ */
+static void add_fd_to_eps(grpc_fd *fd) {
+  GPR_ASSERT(fd->eps == NULL);
+  GPR_TIMER_BEGIN("add_fd_to_eps", 0);
+
+  grpc_error *error = GRPC_ERROR_NONE;
+  size_t idx = (size_t)gpr_atm_no_barrier_fetch_add(&g_next_eps, 1) % g_num_eps;
+  epoll_set *eps = g_epoll_sets[idx];
+
+  gpr_mu_lock(&fd->mu);
+
+  if (fd->orphaned) {
+    gpr_mu_unlock(&fd->mu);
+    return; /* Early out */
+  }
+
+  epoll_set_add_fd_locked(eps, fd, &error);
+  EPS_ADD_REF(eps, "fd");
+  fd->eps = eps;
+
+  GRPC_POLLING_TRACE("add_fd_to_eps (fd: %d, eps idx = %" PRIdPTR ")", fd->fd,
+                     idx);
+  gpr_mu_unlock(&fd->mu);
+
+  GRPC_LOG_IF_ERROR("add_fd_to_eps", error);
+  GPR_TIMER_END("add_fd_to_eps", 0);
+}
+
+static bool init_epoll_sets() {
+  grpc_error *error = GRPC_ERROR_NONE;
+  bool is_success = true;
+
+  g_epoll_sets = (epoll_set **)malloc(g_num_eps * sizeof(epoll_set *));
+
+  for (size_t i = 0; i < g_num_eps; i++) {
+    g_epoll_sets[i] = epoll_set_create(&error);
+    if (g_epoll_sets[i] == NULL) {
+      gpr_log(GPR_ERROR, "Error in creating a epoll set");
+      g_num_eps = i; /* Helps cleanup */
+      shutdown_epoll_sets();
+      is_success = false;
+      goto done;
+    }
+
+    EPS_ADD_REF(g_epoll_sets[i], "init_epoll_sets");
+  }
+
+  gpr_atm_no_barrier_store(&g_next_eps, 0);
+  gpr_mu *mu;
+  pollset_init(&g_read_notifier, &mu);
+
+done:
+  GRPC_LOG_IF_ERROR("init_epoll_sets", error);
+  return is_success;
+}
+
+static void shutdown_epoll_sets() {
+  if (!g_epoll_sets) {
+    return;
+  }
+
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  for (size_t i = 0; i < g_num_eps; i++) {
+    EPS_UNREF(&exec_ctx, g_epoll_sets[i], "shutdown_epoll_sets");
+  }
+  grpc_exec_ctx_flush(&exec_ctx);
+
+  gpr_free(g_epoll_sets);
+  g_epoll_sets = NULL;
+  pollset_destroy(&exec_ctx, &g_read_notifier);
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+static void poller_thread_loop(void *arg) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_error *error = GRPC_ERROR_NONE;
+  epoll_set *eps = (epoll_set *)arg;
+
+  while (!gpr_atm_acq_load(&eps->is_shutdown)) {
+    epoll_set_work(&exec_ctx, eps, &error);
+    grpc_exec_ctx_flush(&exec_ctx);
+  }
+
+  grpc_exec_ctx_finish(&exec_ctx);
+  GRPC_LOG_IF_ERROR("poller_thread_loop", error);
+}
+
+/* g_epoll_sets MUST be initialized before calling this */
+static void start_poller_threads() {
+  GPR_ASSERT(g_epoll_sets);
+
+  gpr_log(GPR_INFO, "Starting poller threads");
+
+  size_t num_threads = g_num_eps * g_num_threads_per_eps;
+  g_poller_threads = (gpr_thd_id *)malloc(num_threads * sizeof(gpr_thd_id));
+  gpr_thd_options options = gpr_thd_options_default();
+  gpr_thd_options_set_joinable(&options);
+
+  for (size_t i = 0; i < num_threads; i++) {
+    gpr_thd_new(&g_poller_threads[i], poller_thread_loop,
+                (void *)g_epoll_sets[i % g_num_eps], &options);
+  }
+}
+
+static void shutdown_poller_threads() {
+  GPR_ASSERT(g_poller_threads);
+  GPR_ASSERT(g_epoll_sets);
+  grpc_error *error = GRPC_ERROR_NONE;
+
+  gpr_log(GPR_INFO, "Shutting down pollers");
+
+  epoll_set *eps = NULL;
+  size_t num_threads = g_num_eps * g_num_threads_per_eps;
+  for (size_t i = 0; i < num_threads; i++) {
+    eps = g_epoll_sets[i];
+    epoll_set_add_wakeup_fd_locked(eps, &epoll_set_wakeup_fd, &error);
+  }
+
+  for (size_t i = 0; i < g_num_eps; i++) {
+    gpr_thd_join(g_poller_threads[i]);
+  }
+
+  GRPC_LOG_IF_ERROR("shutdown_poller_threads", error);
+  gpr_free(g_poller_threads);
+  g_poller_threads = NULL;
+}
+
+/****************************************************************************/
+
+/* It is possible that GLIBC has epoll but the underlying kernel doesn't.
+ * Create a dummy epoll_fd to make sure epoll support is available */
+static bool is_epoll_available() {
+  int fd = epoll_create1(EPOLL_CLOEXEC);
+  if (fd < 0) {
+    gpr_log(
+        GPR_ERROR,
+        "epoll_create1 failed with error: %d. Not using epoll polling engine",
+        fd);
+    return false;
+  }
+  close(fd);
+  return true;
+}
+
+const grpc_event_engine_vtable *grpc_init_epoll_thread_pool_linux(
+    bool requested_explicitly) {
+  if (!requested_explicitly) return NULL;
+
+  if (!grpc_has_wakeup_fd()) {
+    return NULL;
+  }
+
+  if (!is_epoll_available()) {
+    return NULL;
+  }
+
+  fd_global_init();
+
+  if (!GRPC_LOG_IF_ERROR("pollset_global_init", pollset_global_init())) {
+    return NULL;
+  }
+
+  if (!GRPC_LOG_IF_ERROR("epoll_set_global_init", epoll_set_global_init())) {
+    return NULL;
+  }
+
+  if (!init_epoll_sets()) {
+    return NULL;
+  }
+
+  /* TODO (sreek): Maynot be a good idea to start threads here (especially if
+   * this engine doesn't get picked. Consider introducing an engine_init
+   * function in the vtable */
+  start_poller_threads();
+  return &vtable;
+}
+
+#else /* defined(GRPC_LINUX_EPOLL) */
+#if defined(GRPC_POSIX_SOCKET)
+#include "src/core/lib/iomgr/ev_posix.h"
+/* If GRPC_LINUX_EPOLL is not defined, it means epoll is not available. Return
+ * NULL */
+const grpc_event_engine_vtable *grpc_init_epoll_thread_pool_linux(
+    bool requested_explicitly) {
+  return NULL;
+}
+#endif /* defined(GRPC_POSIX_SOCKET) */
+#endif /* !defined(GRPC_LINUX_EPOLL) */
diff --git a/src/core/lib/iomgr/ev_epoll_thread_pool_linux.h b/src/core/lib/iomgr/ev_epoll_thread_pool_linux.h
new file mode 100644
index 0000000000..9af776a52e
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epoll_thread_pool_linux.h
@@ -0,0 +1,43 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_EV_EPOLL_THREAD_POOL_LINUX_H
+#define GRPC_CORE_LIB_IOMGR_EV_EPOLL_THREAD_POOL_LINUX_H
+
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/port.h"
+
+const grpc_event_engine_vtable *grpc_init_epoll_thread_pool_linux(
+    bool requested_explicitly);
+
+#endif /* GRPC_CORE_LIB_IOMGR_EV_EPOLL_THREAD_POOL_LINUX_H */
diff --git a/src/core/lib/iomgr/ev_epollex_linux.c b/src/core/lib/iomgr/ev_epollex_linux.c
new file mode 100644
index 0000000000..7cb6085e25
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epollex_linux.c
@@ -0,0 +1,1511 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/port.h"
+
+/* This polling engine is only relevant on linux kernels supporting epoll() */
+#ifdef GRPC_LINUX_EPOLL
+
+#include "src/core/lib/iomgr/ev_epollex_linux.h"
+
+#include <assert.h>
+#include <errno.h>
+#include <poll.h>
+#include <pthread.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/tls.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/iomgr_internal.h"
+#include "src/core/lib/iomgr/is_epollexclusive_available.h"
+#include "src/core/lib/iomgr/lockfree_event.h"
+#include "src/core/lib/iomgr/sys_epoll_wrapper.h"
+#include "src/core/lib/iomgr/timer.h"
+#include "src/core/lib/iomgr/wakeup_fd_posix.h"
+#include "src/core/lib/iomgr/workqueue.h"
+#include "src/core/lib/profiling/timers.h"
+#include "src/core/lib/support/block_annotate.h"
+#include "src/core/lib/support/spinlock.h"
+
+/*******************************************************************************
+ * Pollset-set sibling link
+ */
+
+typedef enum {
+  PO_POLLING_GROUP,
+  PO_POLLSET_SET,
+  PO_POLLSET,
+  PO_FD, /* ordering is important: we always want to lock pollsets before fds:
+            this guarantees that using an fd as a pollable is safe */
+  PO_EMPTY_POLLABLE,
+  PO_COUNT
+} polling_obj_type;
+
+typedef struct polling_obj polling_obj;
+typedef struct polling_group polling_group;
+
+struct polling_obj {
+  gpr_mu mu;
+  polling_obj_type type;
+  polling_group *group;
+  struct polling_obj *next;
+  struct polling_obj *prev;
+};
+
+struct polling_group {
+  polling_obj po;
+  gpr_refcount refs;
+};
+
+static void po_init(polling_obj *po, polling_obj_type type);
+static void po_destroy(polling_obj *po);
+static void po_join(grpc_exec_ctx *exec_ctx, polling_obj *a, polling_obj *b);
+static int po_cmp(polling_obj *a, polling_obj *b);
+
+static void pg_create(grpc_exec_ctx *exec_ctx, polling_obj **initial_po,
+                      size_t initial_po_count);
+static polling_group *pg_ref(polling_group *pg);
+static void pg_unref(polling_group *pg);
+static void pg_merge(grpc_exec_ctx *exec_ctx, polling_group *a,
+                     polling_group *b);
+static void pg_join(grpc_exec_ctx *exec_ctx, polling_group *pg,
+                    polling_obj *po);
+
+/*******************************************************************************
+ * pollable Declarations
+ */
+
+typedef struct pollable {
+  polling_obj po;
+  int epfd;
+  grpc_wakeup_fd wakeup;
+  grpc_pollset_worker *root_worker;
+} pollable;
+
+static pollable g_empty_pollable;
+
+static void pollable_init(pollable *p, polling_obj_type type);
+static void pollable_destroy(pollable *p);
+/* ensure that p->epfd, p->wakeup are initialized; p->po.mu must be held */
+static grpc_error *pollable_materialize(pollable *p);
+
+/*******************************************************************************
+ * Fd Declarations
+ */
+
+struct grpc_fd {
+  pollable pollable;
+  int fd;
+  /* refst format:
+       bit 0    : 1=Active / 0=Orphaned
+       bits 1-n : refcount
+     Ref/Unref by two to avoid altering the orphaned bit */
+  gpr_atm refst;
+
+  /* Wakeup fd used to wake pollers to check the contents of workqueue_items */
+  grpc_wakeup_fd workqueue_wakeup_fd;
+  grpc_closure_scheduler workqueue_scheduler;
+  /* Spinlock guarding the read end of the workqueue (must be held to pop from
+   * workqueue_items) */
+  gpr_spinlock workqueue_read_mu;
+  /* Queue of closures to be executed */
+  gpr_mpscq workqueue_items;
+  /* Count of items in workqueue_items */
+  gpr_atm workqueue_item_count;
+
+  /* The fd is either closed or we relinquished control of it. In either
+     cases, this indicates that the 'fd' on this structure is no longer
+     valid */
+  gpr_mu orphaned_mu;
+  bool orphaned;
+
+  gpr_atm read_closure;
+  gpr_atm write_closure;
+
+  struct grpc_fd *freelist_next;
+  grpc_closure *on_done_closure;
+
+  /* The pollset that last noticed that the fd is readable. The actual type
+   * stored in this is (grpc_pollset *) */
+  gpr_atm read_notifier_pollset;
+
+  grpc_iomgr_object iomgr_object;
+};
+
+static void fd_global_init(void);
+static void fd_global_shutdown(void);
+
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                              grpc_error *error);
+
+static const grpc_closure_scheduler_vtable workqueue_scheduler_vtable = {
+    workqueue_enqueue, workqueue_enqueue, "workqueue"};
+
+/*******************************************************************************
+ * Pollset Declarations
+ */
+
+typedef struct pollset_worker_link {
+  grpc_pollset_worker *next;
+  grpc_pollset_worker *prev;
+} pollset_worker_link;
+
+typedef enum {
+  PWL_POLLSET,
+  PWL_POLLABLE,
+  POLLSET_WORKER_LINK_COUNT
+} pollset_worker_links;
+
+struct grpc_pollset_worker {
+  bool kicked;
+  bool initialized_cv;
+  pollset_worker_link links[POLLSET_WORKER_LINK_COUNT];
+  gpr_cv cv;
+  grpc_pollset *pollset;
+  pollable *pollable;
+};
+
+struct grpc_pollset {
+  pollable pollable;
+  pollable *current_pollable;
+  bool kicked_without_poller;
+  grpc_closure *shutdown_closure;
+  grpc_pollset_worker *root_worker;
+};
+
+/*******************************************************************************
+ * Pollset-set Declarations
+ */
+struct grpc_pollset_set {
+  polling_obj po;
+};
+
+/*******************************************************************************
+ * Common helpers
+ */
+
+static bool append_error(grpc_error **composite, grpc_error *error,
+                         const char *desc) {
+  if (error == GRPC_ERROR_NONE) return true;
+  if (*composite == GRPC_ERROR_NONE) {
+    *composite = GRPC_ERROR_CREATE_FROM_COPIED_STRING(desc);
+  }
+  *composite = grpc_error_add_child(*composite, error);
+  return false;
+}
+
+/*******************************************************************************
+ * Fd Definitions
+ */
+
+/* We need to keep a freelist not because of any concerns of malloc performance
+ * but instead so that implementations with multiple threads in (for example)
+ * epoll_wait deal with the race between pollset removal and incoming poll
+ * notifications.
+ *
+ * The problem is that the poller ultimately holds a reference to this
+ * object, so it is very difficult to know when is safe to free it, at least
+ * without some expensive synchronization.
+ *
+ * If we keep the object freelisted, in the worst case losing this race just
+ * becomes a spurious read notification on a reused fd.
+ */
+
+/* The alarm system needs to be able to wakeup 'some poller' sometimes
+ * (specifically when a new alarm needs to be triggered earlier than the next
+ * alarm 'epoch'). This wakeup_fd gives us something to alert on when such a
+ * case occurs. */
+
+static grpc_fd *fd_freelist = NULL;
+static gpr_mu fd_freelist_mu;
+
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+#define REF_BY(fd, n, reason) ref_by(fd, n, reason, __FILE__, __LINE__)
+#define UNREF_BY(ec, fd, n, reason) \
+  unref_by(ec, fd, n, reason, __FILE__, __LINE__)
+static void ref_by(grpc_fd *fd, int n, const char *reason, const char *file,
+                   int line) {
+  gpr_log(GPR_DEBUG, "FD %d %p   ref %d %ld -> %ld [%s; %s:%d]", fd->fd,
+          (void *)fd, n, gpr_atm_no_barrier_load(&fd->refst),
+          gpr_atm_no_barrier_load(&fd->refst) + n, reason, file, line);
+#else
+#define REF_BY(fd, n, reason) ref_by(fd, n)
+#define UNREF_BY(ec, fd, n, reason) unref_by(ec, fd, n)
+static void ref_by(grpc_fd *fd, int n) {
+#endif
+  GPR_ASSERT(gpr_atm_no_barrier_fetch_add(&fd->refst, n) > 0);
+}
+
+static void fd_destroy(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
+  grpc_fd *fd = arg;
+  /* Add the fd to the freelist */
+  grpc_iomgr_unregister_object(&fd->iomgr_object);
+  pollable_destroy(&fd->pollable);
+  gpr_mu_destroy(&fd->orphaned_mu);
+  gpr_mu_lock(&fd_freelist_mu);
+  fd->freelist_next = fd_freelist;
+  fd_freelist = fd;
+
+  grpc_lfev_destroy(&fd->read_closure);
+  grpc_lfev_destroy(&fd->write_closure);
+
+  gpr_mu_unlock(&fd_freelist_mu);
+}
+
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+static void unref_by(grpc_exec_ctx *exec_ctx, grpc_fd *fd, int n,
+                     const char *reason, const char *file, int line) {
+  gpr_atm old;
+  gpr_log(GPR_DEBUG, "FD %d %p unref %d %ld -> %ld [%s; %s:%d]", fd->fd,
+          (void *)fd, n, gpr_atm_no_barrier_load(&fd->refst),
+          gpr_atm_no_barrier_load(&fd->refst) - n, reason, file, line);
+#else
+static void unref_by(grpc_exec_ctx *exec_ctx, grpc_fd *fd, int n) {
+  gpr_atm old;
+#endif
+  old = gpr_atm_full_fetch_add(&fd->refst, -n);
+  if (old == n) {
+    grpc_closure_sched(exec_ctx, grpc_closure_create(fd_destroy, fd,
+                                                     grpc_schedule_on_exec_ctx),
+                       GRPC_ERROR_NONE);
+  } else {
+    GPR_ASSERT(old > n);
+  }
+}
+
+static void fd_global_init(void) { gpr_mu_init(&fd_freelist_mu); }
+
+static void fd_global_shutdown(void) {
+  gpr_mu_lock(&fd_freelist_mu);
+  gpr_mu_unlock(&fd_freelist_mu);
+  while (fd_freelist != NULL) {
+    grpc_fd *fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+    gpr_free(fd);
+  }
+  gpr_mu_destroy(&fd_freelist_mu);
+}
+
+static grpc_fd *fd_create(int fd, const char *name) {
+  grpc_fd *new_fd = NULL;
+
+  gpr_mu_lock(&fd_freelist_mu);
+  if (fd_freelist != NULL) {
+    new_fd = fd_freelist;
+    fd_freelist = fd_freelist->freelist_next;
+  }
+  gpr_mu_unlock(&fd_freelist_mu);
+
+  if (new_fd == NULL) {
+    new_fd = gpr_malloc(sizeof(grpc_fd));
+  }
+
+  pollable_init(&new_fd->pollable, PO_FD);
+
+  gpr_atm_rel_store(&new_fd->refst, (gpr_atm)1);
+  new_fd->fd = fd;
+  gpr_mu_init(&new_fd->orphaned_mu);
+  new_fd->orphaned = false;
+  grpc_lfev_init(&new_fd->read_closure);
+  grpc_lfev_init(&new_fd->write_closure);
+  gpr_atm_no_barrier_store(&new_fd->read_notifier_pollset, (gpr_atm)NULL);
+
+  GRPC_LOG_IF_ERROR("fd_create",
+                    grpc_wakeup_fd_init(&new_fd->workqueue_wakeup_fd));
+  new_fd->workqueue_scheduler.vtable = &workqueue_scheduler_vtable;
+  new_fd->workqueue_read_mu = GPR_SPINLOCK_INITIALIZER;
+  gpr_mpscq_init(&new_fd->workqueue_items);
+  gpr_atm_no_barrier_store(&new_fd->workqueue_item_count, 0);
+
+  new_fd->freelist_next = NULL;
+  new_fd->on_done_closure = NULL;
+
+  char *fd_name;
+  gpr_asprintf(&fd_name, "%s fd=%d", name, fd);
+  grpc_iomgr_register_object(&new_fd->iomgr_object, fd_name);
+#ifdef GRPC_FD_REF_COUNT_DEBUG
+  gpr_log(GPR_DEBUG, "FD %d %p create %s", fd, (void *)new_fd, fd_name);
+#endif
+  gpr_free(fd_name);
+  return new_fd;
+}
+
+static int fd_wrapped_fd(grpc_fd *fd) {
+  int ret_fd = -1;
+  gpr_mu_lock(&fd->orphaned_mu);
+  if (!fd->orphaned) {
+    ret_fd = fd->fd;
+  }
+  gpr_mu_unlock(&fd->orphaned_mu);
+
+  return ret_fd;
+}
+
+static void fd_orphan(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                      grpc_closure *on_done, int *release_fd,
+                      const char *reason) {
+  bool is_fd_closed = false;
+  grpc_error *error = GRPC_ERROR_NONE;
+
+  gpr_mu_lock(&fd->pollable.po.mu);
+  gpr_mu_lock(&fd->orphaned_mu);
+  fd->on_done_closure = on_done;
+
+  /* If release_fd is not NULL, we should be relinquishing control of the file
+     descriptor fd->fd (but we still own the grpc_fd structure). */
+  if (release_fd != NULL) {
+    *release_fd = fd->fd;
+  } else {
+    close(fd->fd);
+    is_fd_closed = true;
+  }
+
+  fd->orphaned = true;
+
+  if (!is_fd_closed) {
+    gpr_log(GPR_DEBUG, "TODO: handle fd removal?");
+  }
+
+  /* Remove the active status but keep referenced. We want this grpc_fd struct
+     to be alive (and not added to freelist) until the end of this function */
+  REF_BY(fd, 1, reason);
+
+  grpc_closure_sched(exec_ctx, fd->on_done_closure, GRPC_ERROR_REF(error));
+
+  gpr_mu_unlock(&fd->orphaned_mu);
+  gpr_mu_unlock(&fd->pollable.po.mu);
+  UNREF_BY(exec_ctx, fd, 2, reason); /* Drop the reference */
+  GRPC_LOG_IF_ERROR("fd_orphan", GRPC_ERROR_REF(error));
+  GRPC_ERROR_UNREF(error);
+}
+
+static grpc_pollset *fd_get_read_notifier_pollset(grpc_exec_ctx *exec_ctx,
+                                                  grpc_fd *fd) {
+  gpr_atm notifier = gpr_atm_acq_load(&fd->read_notifier_pollset);
+  return (grpc_pollset *)notifier;
+}
+
+static bool fd_is_shutdown(grpc_fd *fd) {
+  return grpc_lfev_is_shutdown(&fd->read_closure);
+}
+
+/* Might be called multiple times */
+static void fd_shutdown(grpc_exec_ctx *exec_ctx, grpc_fd *fd, grpc_error *why) {
+  if (grpc_lfev_set_shutdown(exec_ctx, &fd->read_closure,
+                             GRPC_ERROR_REF(why))) {
+    shutdown(fd->fd, SHUT_RDWR);
+    grpc_lfev_set_shutdown(exec_ctx, &fd->write_closure, GRPC_ERROR_REF(why));
+  }
+  GRPC_ERROR_UNREF(why);
+}
+
+static void fd_notify_on_read(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                              grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->read_closure, closure);
+}
+
+static void fd_notify_on_write(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                               grpc_closure *closure) {
+  grpc_lfev_notify_on(exec_ctx, &fd->write_closure, closure);
+}
+
+static grpc_workqueue *fd_get_workqueue(grpc_fd *fd) {
+  REF_BY(fd, 2, "return_workqueue");
+  return (grpc_workqueue *)fd;
+}
+
+#ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue,
+                                     const char *file, int line,
+                                     const char *reason) {
+  if (workqueue != NULL) {
+    ref_by((grpc_fd *)workqueue, 2, file, line, reason);
+  }
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
+                            const char *file, int line, const char *reason) {
+  if (workqueue != NULL) {
+    unref_by(exec_ctx, (grpc_fd *)workqueue, 2, file, line, reason);
+  }
+}
+#else
+static grpc_workqueue *workqueue_ref(grpc_workqueue *workqueue) {
+  if (workqueue != NULL) {
+    ref_by((grpc_fd *)workqueue, 2);
+  }
+  return workqueue;
+}
+
+static void workqueue_unref(grpc_exec_ctx *exec_ctx,
+                            grpc_workqueue *workqueue) {
+  if (workqueue != NULL) {
+    unref_by(exec_ctx, (grpc_fd *)workqueue, 2);
+  }
+}
+#endif
+
+static void workqueue_wakeup(grpc_fd *fd) {
+  GRPC_LOG_IF_ERROR("workqueue_enqueue",
+                    grpc_wakeup_fd_wakeup(&fd->workqueue_wakeup_fd));
+}
+
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                              grpc_error *error) {
+  GPR_TIMER_BEGIN("workqueue.enqueue", 0);
+  grpc_fd *fd = (grpc_fd *)(((char *)closure->scheduler) -
+                            offsetof(grpc_fd, workqueue_scheduler));
+  REF_BY(fd, 2, "workqueue_enqueue");
+  gpr_atm last = gpr_atm_no_barrier_fetch_add(&fd->workqueue_item_count, 1);
+  closure->error_data.error = error;
+  gpr_mpscq_push(&fd->workqueue_items, &closure->next_data.atm_next);
+  if (last == 0) {
+    workqueue_wakeup(fd);
+  }
+  UNREF_BY(exec_ctx, fd, 2, "workqueue_enqueue");
+}
+
+static void fd_invoke_workqueue(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
+  /* handle spurious wakeups */
+  if (!gpr_spinlock_trylock(&fd->workqueue_read_mu)) return;
+  gpr_mpscq_node *n = gpr_mpscq_pop(&fd->workqueue_items);
+  gpr_spinlock_unlock(&fd->workqueue_read_mu);
+  if (n != NULL) {
+    if (gpr_atm_full_fetch_add(&fd->workqueue_item_count, -1) > 1) {
+      workqueue_wakeup(fd);
+    }
+    grpc_closure *c = (grpc_closure *)n;
+    grpc_error *error = c->error_data.error;
+#ifndef NDEBUG
+    c->scheduled = false;
+#endif
+    c->cb(exec_ctx, c->cb_arg, error);
+    GRPC_ERROR_UNREF(error);
+  } else if (gpr_atm_no_barrier_load(&fd->workqueue_item_count) > 0) {
+    /* n == NULL might mean there's work but it's not available to be popped
+     * yet - try to ensure another workqueue wakes up to check shortly if so
+     */
+    workqueue_wakeup(fd);
+  }
+}
+
+static grpc_closure_scheduler *workqueue_scheduler(grpc_workqueue *workqueue) {
+  return &((grpc_fd *)workqueue)->workqueue_scheduler;
+}
+
+/*******************************************************************************
+ * Pollable Definitions
+ */
+
+static void pollable_init(pollable *p, polling_obj_type type) {
+  po_init(&p->po, type);
+  p->root_worker = NULL;
+  p->epfd = -1;
+}
+
+static void pollable_destroy(pollable *p) {
+  po_destroy(&p->po);
+  if (p->epfd != -1) {
+    close(p->epfd);
+    grpc_wakeup_fd_destroy(&p->wakeup);
+  }
+}
+
+/* ensure that p->epfd, p->wakeup are initialized; p->po.mu must be held */
+static grpc_error *pollable_materialize(pollable *p) {
+  if (p->epfd == -1) {
+    int new_epfd = epoll_create1(EPOLL_CLOEXEC);
+    if (new_epfd < 0) {
+      return GRPC_OS_ERROR(errno, "epoll_create1");
+    }
+    grpc_error *err = grpc_wakeup_fd_init(&p->wakeup);
+    if (err != GRPC_ERROR_NONE) {
+      close(new_epfd);
+      return err;
+    }
+    struct epoll_event ev = {.events = (uint32_t)(EPOLLIN | EPOLLET),
+                             .data.ptr = &p->wakeup};
+    if (epoll_ctl(new_epfd, EPOLL_CTL_ADD, p->wakeup.read_fd, &ev) != 0) {
+      err = GRPC_OS_ERROR(errno, "epoll_ctl");
+      close(new_epfd);
+      grpc_wakeup_fd_destroy(&p->wakeup);
+      return err;
+    }
+
+    p->epfd = new_epfd;
+  }
+  return GRPC_ERROR_NONE;
+}
+
+/* pollable must be materialized */
+static grpc_error *pollable_add_fd(pollable *p, grpc_fd *fd) {
+  grpc_error *error = GRPC_ERROR_NONE;
+  static const char *err_desc = "pollable_add_fd";
+  const int epfd = p->epfd;
+  GPR_ASSERT(epfd != -1);
+
+  if (GRPC_TRACER_ON(grpc_polling_trace)) {
+    gpr_log(GPR_DEBUG, "add fd %p to pollable %p", fd, p);
+  }
+
+  gpr_mu_lock(&fd->orphaned_mu);
+  if (fd->orphaned) {
+    gpr_mu_unlock(&fd->orphaned_mu);
+    return GRPC_ERROR_NONE;
+  }
+  struct epoll_event ev_fd = {
+      .events = (uint32_t)(EPOLLET | EPOLLIN | EPOLLOUT | EPOLLEXCLUSIVE),
+      .data.ptr = fd};
+  if (epoll_ctl(epfd, EPOLL_CTL_ADD, fd->fd, &ev_fd) != 0) {
+    switch (errno) {
+      case EEXIST: /* if this fd is already in the epoll set, the workqueue fd
+                      must also be - just return */
+        gpr_mu_unlock(&fd->orphaned_mu);
+        return GRPC_ERROR_NONE;
+      default:
+        append_error(&error, GRPC_OS_ERROR(errno, "epoll_ctl"), err_desc);
+    }
+  }
+  struct epoll_event ev_wq = {
+      .events = (uint32_t)(EPOLLET | EPOLLIN | EPOLLEXCLUSIVE),
+      .data.ptr = (void *)(1 + (intptr_t)fd)};
+  if (epoll_ctl(epfd, EPOLL_CTL_ADD, fd->workqueue_wakeup_fd.read_fd, &ev_wq) !=
+      0) {
+    switch (errno) {
+      case EEXIST: /* if the workqueue fd is already in the epoll set we're ok
+                      - no need to do anything special */
+        break;
+      default:
+        append_error(&error, GRPC_OS_ERROR(errno, "epoll_ctl"), err_desc);
+    }
+  }
+  gpr_mu_unlock(&fd->orphaned_mu);
+
+  return error;
+}
+
+/*******************************************************************************
+ * Pollset Definitions
+ */
+
+GPR_TLS_DECL(g_current_thread_pollset);
+GPR_TLS_DECL(g_current_thread_worker);
+
+/* Global state management */
+static grpc_error *pollset_global_init(void) {
+  gpr_tls_init(&g_current_thread_pollset);
+  gpr_tls_init(&g_current_thread_worker);
+  pollable_init(&g_empty_pollable, PO_EMPTY_POLLABLE);
+  return GRPC_ERROR_NONE;
+}
+
+static void pollset_global_shutdown(void) {
+  pollable_destroy(&g_empty_pollable);
+  gpr_tls_destroy(&g_current_thread_pollset);
+  gpr_tls_destroy(&g_current_thread_worker);
+}
+
+static grpc_error *pollset_kick_all(grpc_pollset *pollset) {
+  grpc_error *error = GRPC_ERROR_NONE;
+  if (pollset->root_worker != NULL) {
+    grpc_pollset_worker *worker = pollset->root_worker;
+    do {
+      if (worker->pollable != &pollset->pollable) {
+        gpr_mu_lock(&worker->pollable->po.mu);
+      }
+      if (worker->initialized_cv) {
+        worker->kicked = true;
+        gpr_cv_signal(&worker->cv);
+      } else {
+        append_error(&error, grpc_wakeup_fd_wakeup(&worker->pollable->wakeup),
+                     "pollset_shutdown");
+      }
+      if (worker->pollable != &pollset->pollable) {
+        gpr_mu_unlock(&worker->pollable->po.mu);
+      }
+
+      worker = worker->links[PWL_POLLSET].next;
+    } while (worker != pollset->root_worker);
+  }
+  return error;
+}
+
+static grpc_error *pollset_kick_inner(grpc_pollset *pollset, pollable *p,
+                                      grpc_pollset_worker *specific_worker) {
+  if (GRPC_TRACER_ON(grpc_polling_trace)) {
+    gpr_log(GPR_DEBUG,
+            "PS:%p kick %p tls_pollset=%p tls_worker=%p "
+            "root_worker=(pollset:%p pollable:%p)",
+            p, specific_worker, (void *)gpr_tls_get(&g_current_thread_pollset),
+            (void *)gpr_tls_get(&g_current_thread_worker), pollset->root_worker,
+            p->root_worker);
+  }
+  if (specific_worker == NULL) {
+    if (gpr_tls_get(&g_current_thread_pollset) != (intptr_t)pollset) {
+      if (pollset->root_worker == NULL) {
+        if (GRPC_TRACER_ON(grpc_polling_trace)) {
+          gpr_log(GPR_DEBUG, "PS:%p kicked_any_without_poller", p);
+        }
+        pollset->kicked_without_poller = true;
+        return GRPC_ERROR_NONE;
+      } else {
+        if (GRPC_TRACER_ON(grpc_polling_trace)) {
+          gpr_log(GPR_DEBUG, "PS:%p kicked_any_via_wakeup_fd", p);
+        }
+        grpc_error *err = pollable_materialize(p);
+        if (err != GRPC_ERROR_NONE) return err;
+        return grpc_wakeup_fd_wakeup(&p->wakeup);
+      }
+    } else {
+      if (GRPC_TRACER_ON(grpc_polling_trace)) {
+        gpr_log(GPR_DEBUG, "PS:%p kicked_any_but_awake", p);
+      }
+      return GRPC_ERROR_NONE;
+    }
+  } else if (specific_worker->kicked) {
+    if (GRPC_TRACER_ON(grpc_polling_trace)) {
+      gpr_log(GPR_DEBUG, "PS:%p kicked_specific_but_already_kicked", p);
+    }
+    return GRPC_ERROR_NONE;
+  } else if (gpr_tls_get(&g_current_thread_worker) ==
+             (intptr_t)specific_worker) {
+    if (GRPC_TRACER_ON(grpc_polling_trace)) {
+      gpr_log(GPR_DEBUG, "PS:%p kicked_specific_but_awake", p);
+    }
+    specific_worker->kicked = true;
+    return GRPC_ERROR_NONE;
+  } else if (specific_worker == p->root_worker) {
+    if (GRPC_TRACER_ON(grpc_polling_trace)) {
+      gpr_log(GPR_DEBUG, "PS:%p kicked_specific_via_wakeup_fd", p);
+    }
+    grpc_error *err = pollable_materialize(p);
+    if (err != GRPC_ERROR_NONE) return err;
+    specific_worker->kicked = true;
+    return grpc_wakeup_fd_wakeup(&p->wakeup);
+  } else {
+    if (GRPC_TRACER_ON(grpc_polling_trace)) {
+      gpr_log(GPR_DEBUG, "PS:%p kicked_specific_via_cv", p);
+    }
+    specific_worker->kicked = true;
+    gpr_cv_signal(&specific_worker->cv);
+    return GRPC_ERROR_NONE;
+  }
+}
+
+/* p->po.mu must be held before calling this function */
+static grpc_error *pollset_kick(grpc_pollset *pollset,
+                                grpc_pollset_worker *specific_worker) {
+  pollable *p = pollset->current_pollable;
+  if (p != &pollset->pollable) {
+    gpr_mu_lock(&p->po.mu);
+  }
+  grpc_error *error = pollset_kick_inner(pollset, p, specific_worker);
+  if (p != &pollset->pollable) {
+    gpr_mu_unlock(&p->po.mu);
+  }
+  return error;
+}
+
+static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
+  pollable_init(&pollset->pollable, PO_POLLSET);
+  pollset->current_pollable = &g_empty_pollable;
+  pollset->kicked_without_poller = false;
+  pollset->shutdown_closure = NULL;
+  pollset->root_worker = NULL;
+  *mu = &pollset->pollable.po.mu;
+}
+
+/* Convert a timespec to milliseconds:
+   - Very small or negative poll times are clamped to zero to do a non-blocking
+     poll (which becomes spin polling)
+   - Other small values are rounded up to one millisecond
+   - Longer than a millisecond polls are rounded up to the next nearest
+     millisecond to avoid spinning
+   - Infinite timeouts are converted to -1 */
+static int poll_deadline_to_millis_timeout(gpr_timespec deadline,
+                                           gpr_timespec now) {
+  gpr_timespec timeout;
+  if (gpr_time_cmp(deadline, gpr_inf_future(deadline.clock_type)) == 0) {
+    return -1;
+  }
+
+  if (gpr_time_cmp(deadline, now) <= 0) {
+    return 0;
+  }
+
+  static const gpr_timespec round_up = {
+      .clock_type = GPR_TIMESPAN, .tv_sec = 0, .tv_nsec = GPR_NS_PER_MS - 1};
+  timeout = gpr_time_sub(deadline, now);
+  int millis = gpr_time_to_millis(gpr_time_add(timeout, round_up));
+  return millis >= 1 ? millis : 1;
+}
+
+static void fd_become_readable(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
+                               grpc_pollset *notifier) {
+  grpc_lfev_set_ready(exec_ctx, &fd->read_closure);
+
+  /* Note, it is possible that fd_become_readable might be called twice with
+     different 'notifier's when an fd becomes readable and it is in two epoll
+     sets (This can happen briefly during polling island merges). In such cases
+     it does not really matter which notifer is set as the read_notifier_pollset
+     (They would both point to the same polling island anyway) */
+  /* Use release store to match with acquire load in fd_get_read_notifier */
+  gpr_atm_rel_store(&fd->read_notifier_pollset, (gpr_atm)notifier);
+}
+
+static void fd_become_writable(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
+  grpc_lfev_set_ready(exec_ctx, &fd->write_closure);
+}
+
+static grpc_error *fd_become_pollable_locked(grpc_fd *fd) {
+  grpc_error *error = GRPC_ERROR_NONE;
+  static const char *err_desc = "fd_become_pollable";
+  if (append_error(&error, pollable_materialize(&fd->pollable), err_desc)) {
+    append_error(&error, pollable_add_fd(&fd->pollable, fd), err_desc);
+  }
+  return error;
+}
+
+static void pollset_maybe_finish_shutdown(grpc_exec_ctx *exec_ctx,
+                                          grpc_pollset *pollset) {
+  if (pollset->shutdown_closure != NULL && pollset->root_worker == NULL) {
+    grpc_closure_sched(exec_ctx, pollset->shutdown_closure, GRPC_ERROR_NONE);
+    pollset->shutdown_closure = NULL;
+  }
+}
+
+/* pollset->po.mu lock must be held by the caller before calling this */
+static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                             grpc_closure *closure) {
+  GPR_ASSERT(pollset->shutdown_closure == NULL);
+  pollset->shutdown_closure = closure;
+  GRPC_LOG_IF_ERROR("pollset_shutdown", pollset_kick_all(pollset));
+  pollset_maybe_finish_shutdown(exec_ctx, pollset);
+}
+
+static bool pollset_is_pollable_fd(grpc_pollset *pollset, pollable *p) {
+  return p != &g_empty_pollable && p != &pollset->pollable;
+}
+
+/* pollset_shutdown is guaranteed to be called before pollset_destroy. */
+static void pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
+  pollable_destroy(&pollset->pollable);
+  if (pollset_is_pollable_fd(pollset, pollset->current_pollable)) {
+    UNREF_BY(exec_ctx, (grpc_fd *)pollset->current_pollable, 2,
+             "pollset_pollable");
+  }
+}
+
+#define MAX_EPOLL_EVENTS 100
+
+static grpc_error *pollset_epoll(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                                 pollable *p, gpr_timespec now,
+                                 gpr_timespec deadline) {
+  struct epoll_event events[MAX_EPOLL_EVENTS];
+  static const char *err_desc = "pollset_poll";
+
+  int timeout = poll_deadline_to_millis_timeout(deadline, now);
+
+  if (GRPC_TRACER_ON(grpc_polling_trace)) {
+    gpr_log(GPR_DEBUG, "PS:%p poll %p for %dms", pollset, p, timeout);
+  }
+
+  if (timeout != 0) {
+    GRPC_SCHEDULING_START_BLOCKING_REGION;
+  }
+  int r;
+  do {
+    r = epoll_wait(p->epfd, events, MAX_EPOLL_EVENTS, timeout);
+  } while (r < 0 && errno == EINTR);
+  if (timeout != 0) {
+    GRPC_SCHEDULING_END_BLOCKING_REGION;
+  }
+
+  if (r < 0) return GRPC_OS_ERROR(errno, "epoll_wait");
+
+  if (GRPC_TRACER_ON(grpc_polling_trace)) {
+    gpr_log(GPR_DEBUG, "PS:%p poll %p got %d events", pollset, p, r);
+  }
+
+  grpc_error *error = GRPC_ERROR_NONE;
+  for (int i = 0; i < r; i++) {
+    void *data_ptr = events[i].data.ptr;
+    if (data_ptr == &p->wakeup) {
+      if (GRPC_TRACER_ON(grpc_polling_trace)) {
+        gpr_log(GPR_DEBUG, "PS:%p poll %p got pollset_wakeup", pollset, p);
+      }
+      append_error(&error, grpc_wakeup_fd_consume_wakeup(&p->wakeup), err_desc);
+    } else {
+      grpc_fd *fd = (grpc_fd *)(((intptr_t)data_ptr) & ~(intptr_t)1);
+      bool is_workqueue = (((intptr_t)data_ptr) & 1) != 0;
+      bool cancel = (events[i].events & (EPOLLERR | EPOLLHUP)) != 0;
+      bool read_ev = (events[i].events & (EPOLLIN | EPOLLPRI)) != 0;
+      bool write_ev = (events[i].events & EPOLLOUT) != 0;
+      if (GRPC_TRACER_ON(grpc_polling_trace)) {
+        gpr_log(GPR_DEBUG,
+                "PS:%p poll %p got fd %p: is_wq=%d cancel=%d read=%d "
+                "write=%d",
+                pollset, p, fd, is_workqueue, cancel, read_ev, write_ev);
+      }
+      if (is_workqueue) {
+        append_error(&error,
+                     grpc_wakeup_fd_consume_wakeup(&fd->workqueue_wakeup_fd),
+                     err_desc);
+        fd_invoke_workqueue(exec_ctx, fd);
+      } else {
+        if (read_ev || cancel) {
+          fd_become_readable(exec_ctx, fd, pollset);
+        }
+        if (write_ev || cancel) {
+          fd_become_writable(exec_ctx, fd);
+        }
+      }
+    }
+  }
+
+  return error;
+}
+
+/* Return true if first in list */
+static bool worker_insert(grpc_pollset_worker **root, pollset_worker_links link,
+                          grpc_pollset_worker *worker) {
+  if (*root == NULL) {
+    *root = worker;
+    worker->links[link].next = worker->links[link].prev = worker;
+    return true;
+  } else {
+    worker->links[link].next = *root;
+    worker->links[link].prev = worker->links[link].next->links[link].prev;
+    worker->links[link].next->links[link].prev = worker;
+    worker->links[link].prev->links[link].next = worker;
+    return false;
+  }
+}
+
+/* Return true if last in list */
+typedef enum { EMPTIED, NEW_ROOT, REMOVED } worker_remove_result;
+
+static worker_remove_result worker_remove(grpc_pollset_worker **root,
+                                          pollset_worker_links link,
+                                          grpc_pollset_worker *worker) {
+  if (worker == *root) {
+    if (worker == worker->links[link].next) {
+      *root = NULL;
+      return EMPTIED;
+    } else {
+      *root = worker->links[link].next;
+      worker->links[link].prev->links[link].next = worker->links[link].next;
+      worker->links[link].next->links[link].prev = worker->links[link].prev;
+      return NEW_ROOT;
+    }
+  } else {
+    worker->links[link].prev->links[link].next = worker->links[link].next;
+    worker->links[link].next->links[link].prev = worker->links[link].prev;
+    return REMOVED;
+  }
+}
+
+/* Return true if this thread should poll */
+static bool begin_worker(grpc_pollset *pollset, grpc_pollset_worker *worker,
+                         grpc_pollset_worker **worker_hdl, gpr_timespec *now,
+                         gpr_timespec deadline) {
+  bool do_poll = true;
+  if (worker_hdl != NULL) *worker_hdl = worker;
+  worker->initialized_cv = false;
+  worker->kicked = false;
+  worker->pollset = pollset;
+  worker->pollable = pollset->current_pollable;
+
+  if (pollset_is_pollable_fd(pollset, worker->pollable)) {
+    REF_BY((grpc_fd *)worker->pollable, 2, "one_poll");
+  }
+
+  worker_insert(&pollset->root_worker, PWL_POLLSET, worker);
+  if (!worker_insert(&worker->pollable->root_worker, PWL_POLLABLE, worker)) {
+    worker->initialized_cv = true;
+    gpr_cv_init(&worker->cv);
+    if (worker->pollable != &pollset->pollable) {
+      gpr_mu_unlock(&pollset->pollable.po.mu);
+    }
+    if (GRPC_TRACER_ON(grpc_polling_trace) &&
+        worker->pollable->root_worker != worker) {
+      gpr_log(GPR_DEBUG, "PS:%p wait %p w=%p for %dms", pollset,
+              worker->pollable, worker,
+              poll_deadline_to_millis_timeout(deadline, *now));
+    }
+    while (do_poll && worker->pollable->root_worker != worker) {
+      if (gpr_cv_wait(&worker->cv, &worker->pollable->po.mu, deadline)) {
+        if (GRPC_TRACER_ON(grpc_polling_trace)) {
+          gpr_log(GPR_DEBUG, "PS:%p timeout_wait %p w=%p", pollset,
+                  worker->pollable, worker);
+        }
+        do_poll = false;
+      } else if (worker->kicked) {
+        if (GRPC_TRACER_ON(grpc_polling_trace)) {
+          gpr_log(GPR_DEBUG, "PS:%p wakeup %p w=%p", pollset, worker->pollable,
+                  worker);
+        }
+        do_poll = false;
+      } else if (GRPC_TRACER_ON(grpc_polling_trace) &&
+                 worker->pollable->root_worker != worker) {
+        gpr_log(GPR_DEBUG, "PS:%p spurious_wakeup %p w=%p", pollset,
+                worker->pollable, worker);
+      }
+    }
+    if (worker->pollable != &pollset->pollable) {
+      gpr_mu_unlock(&worker->pollable->po.mu);
+      gpr_mu_lock(&pollset->pollable.po.mu);
+      gpr_mu_lock(&worker->pollable->po.mu);
+    }
+    *now = gpr_now(now->clock_type);
+  }
+
+  return do_poll && pollset->shutdown_closure == NULL &&
+         pollset->current_pollable == worker->pollable;
+}
+
+static void end_worker(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                       grpc_pollset_worker *worker,
+                       grpc_pollset_worker **worker_hdl) {
+  if (NEW_ROOT ==
+      worker_remove(&worker->pollable->root_worker, PWL_POLLABLE, worker)) {
+    gpr_cv_signal(&worker->pollable->root_worker->cv);
+  }
+  if (worker->initialized_cv) {
+    gpr_cv_destroy(&worker->cv);
+  }
+  if (pollset_is_pollable_fd(pollset, worker->pollable)) {
+    UNREF_BY(exec_ctx, (grpc_fd *)worker->pollable, 2, "one_poll");
+  }
+  if (EMPTIED == worker_remove(&pollset->root_worker, PWL_POLLSET, worker)) {
+    pollset_maybe_finish_shutdown(exec_ctx, pollset);
+  }
+}
+
+/* pollset->po.mu lock must be held by the caller before calling this.
+   The function pollset_work() may temporarily release the lock (pollset->po.mu)
+   during the course of its execution but it will always re-acquire the lock and
+   ensure that it is held by the time the function returns */
+static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                                grpc_pollset_worker **worker_hdl,
+                                gpr_timespec now, gpr_timespec deadline) {
+  grpc_pollset_worker worker;
+  if (0 && GRPC_TRACER_ON(grpc_polling_trace)) {
+    gpr_log(GPR_DEBUG, "PS:%p work hdl=%p worker=%p now=%" PRId64
+                       ".%09d deadline=%" PRId64 ".%09d kwp=%d root_worker=%p",
+            pollset, worker_hdl, &worker, now.tv_sec, now.tv_nsec,
+            deadline.tv_sec, deadline.tv_nsec, pollset->kicked_without_poller,
+            pollset->root_worker);
+  }
+  grpc_error *error = GRPC_ERROR_NONE;
+  static const char *err_desc = "pollset_work";
+  if (pollset->kicked_without_poller) {
+    pollset->kicked_without_poller = false;
+    return GRPC_ERROR_NONE;
+  }
+  if (pollset->current_pollable != &pollset->pollable) {
+    gpr_mu_lock(&pollset->current_pollable->po.mu);
+  }
+  if (begin_worker(pollset, &worker, worker_hdl, &now, deadline)) {
+    gpr_tls_set(&g_current_thread_pollset, (intptr_t)pollset);
+    gpr_tls_set(&g_current_thread_worker, (intptr_t)&worker);
+    GPR_ASSERT(!pollset->shutdown_closure);
+    append_error(&error, pollable_materialize(worker.pollable), err_desc);
+    if (worker.pollable != &pollset->pollable) {
+      gpr_mu_unlock(&worker.pollable->po.mu);
+    }
+    gpr_mu_unlock(&pollset->pollable.po.mu);
+    append_error(&error, pollset_epoll(exec_ctx, pollset, worker.pollable, now,
+                                       deadline),
+                 err_desc);
+    grpc_exec_ctx_flush(exec_ctx);
+    gpr_mu_lock(&pollset->pollable.po.mu);
+    if (worker.pollable != &pollset->pollable) {
+      gpr_mu_lock(&worker.pollable->po.mu);
+    }
+    gpr_tls_set(&g_current_thread_pollset, 0);
+    gpr_tls_set(&g_current_thread_worker, 0);
+    pollset_maybe_finish_shutdown(exec_ctx, pollset);
+  }
+  end_worker(exec_ctx, pollset, &worker, worker_hdl);
+  if (worker.pollable != &pollset->pollable) {
+    gpr_mu_unlock(&worker.pollable->po.mu);
+  }
+  return error;
+}
+
+static void unref_fd_no_longer_poller(grpc_exec_ctx *exec_ctx, void *arg,
+                                      grpc_error *error) {
+  grpc_fd *fd = arg;
+  UNREF_BY(exec_ctx, fd, 2, "pollset_pollable");
+}
+
+/* expects pollsets locked, flag whether fd is locked or not */
+static grpc_error *pollset_add_fd_locked(grpc_exec_ctx *exec_ctx,
+                                         grpc_pollset *pollset, grpc_fd *fd,
+                                         bool fd_locked) {
+  static const char *err_desc = "pollset_add_fd";
+  grpc_error *error = GRPC_ERROR_NONE;
+  if (pollset->current_pollable == &g_empty_pollable) {
+    if (GRPC_TRACER_ON(grpc_polling_trace))
+      gpr_log(GPR_DEBUG,
+              "PS:%p add fd %p; transition pollable from empty to fd", pollset,
+              fd);
+    /* empty pollable --> single fd pollable */
+    append_error(&error, pollset_kick_all(pollset), err_desc);
+    pollset->current_pollable = &fd->pollable;
+    if (!fd_locked) gpr_mu_lock(&fd->pollable.po.mu);
+    append_error(&error, fd_become_pollable_locked(fd), err_desc);
+    if (!fd_locked) gpr_mu_unlock(&fd->pollable.po.mu);
+    REF_BY(fd, 2, "pollset_pollable");
+  } else if (pollset->current_pollable == &pollset->pollable) {
+    if (GRPC_TRACER_ON(grpc_polling_trace))
+      gpr_log(GPR_DEBUG, "PS:%p add fd %p; already multipolling", pollset, fd);
+    append_error(&error, pollable_add_fd(pollset->current_pollable, fd),
+                 err_desc);
+  } else if (pollset->current_pollable != &fd->pollable) {
+    grpc_fd *had_fd = (grpc_fd *)pollset->current_pollable;
+    if (GRPC_TRACER_ON(grpc_polling_trace))
+      gpr_log(GPR_DEBUG,
+              "PS:%p add fd %p; transition pollable from fd %p to multipoller",
+              pollset, fd, had_fd);
+    append_error(&error, pollset_kick_all(pollset), err_desc);
+    pollset->current_pollable = &pollset->pollable;
+    if (append_error(&error, pollable_materialize(&pollset->pollable),
+                     err_desc)) {
+      pollable_add_fd(&pollset->pollable, had_fd);
+      pollable_add_fd(&pollset->pollable, fd);
+    }
+    grpc_closure_sched(exec_ctx,
+                       grpc_closure_create(unref_fd_no_longer_poller, had_fd,
+                                           grpc_schedule_on_exec_ctx),
+                       GRPC_ERROR_NONE);
+  }
+  return error;
+}
+
+static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
+                           grpc_fd *fd) {
+  gpr_mu_lock(&pollset->pollable.po.mu);
+  grpc_error *error = pollset_add_fd_locked(exec_ctx, pollset, fd, false);
+  gpr_mu_unlock(&pollset->pollable.po.mu);
+  GRPC_LOG_IF_ERROR("pollset_add_fd", error);
+}
+
+/*******************************************************************************
+ * Pollset-set Definitions
+ */
+
+static grpc_pollset_set *pollset_set_create(void) {
+  grpc_pollset_set *pss = gpr_zalloc(sizeof(*pss));
+  po_init(&pss->po, PO_POLLSET_SET);
+  return pss;
+}
+
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pss) {
+  po_destroy(&pss->po);
+  gpr_free(pss);
+}
+
+static void pollset_set_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {
+  po_join(exec_ctx, &pss->po, &fd->pollable.po);
+}
+
+static void pollset_set_del_fd(grpc_exec_ctx *exec_ctx, grpc_pollset_set *pss,
+                               grpc_fd *fd) {}
+
+static void pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {
+  po_join(exec_ctx, &pss->po, &ps->pollable.po);
+}
+
+static void pollset_set_del_pollset(grpc_exec_ctx *exec_ctx,
+                                    grpc_pollset_set *pss, grpc_pollset *ps) {}
+
+static void pollset_set_add_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {
+  po_join(exec_ctx, &bag->po, &item->po);
+}
+
+static void pollset_set_del_pollset_set(grpc_exec_ctx *exec_ctx,
+                                        grpc_pollset_set *bag,
+                                        grpc_pollset_set *item) {}
+
+static void po_init(polling_obj *po, polling_obj_type type) {
+  gpr_mu_init(&po->mu);
+  po->type = type;
+  po->group = NULL;
+  po->next = po;
+  po->prev = po;
+}
+
+static polling_group *pg_lock_latest(polling_group *pg) {
+  /* assumes pg unlocked; consumes ref, returns ref */
+  gpr_mu_lock(&pg->po.mu);
+  while (pg->po.group != NULL) {
+    polling_group *new_pg = pg_ref(pg->po.group);
+    gpr_mu_unlock(&pg->po.mu);
+    pg_unref(pg);
+    pg = new_pg;
+    gpr_mu_lock(&pg->po.mu);
+  }
+  return pg;
+}
+
+static void po_destroy(polling_obj *po) {
+  if (po->group != NULL) {
+    polling_group *pg = pg_lock_latest(po->group);
+    po->prev->next = po->next;
+    po->next->prev = po->prev;
+    gpr_mu_unlock(&pg->po.mu);
+    pg_unref(pg);
+  }
+  gpr_mu_destroy(&po->mu);
+}
+
+static polling_group *pg_ref(polling_group *pg) {
+  gpr_ref(&pg->refs);
+  return pg;
+}
+
+static void pg_unref(polling_group *pg) {
+  if (gpr_unref(&pg->refs)) {
+    po_destroy(&pg->po);
+    gpr_free(pg);
+  }
+}
+
+static int po_cmp(polling_obj *a, polling_obj *b) {
+  if (a == b) return 0;
+  if (a->type < b->type) return -1;
+  if (a->type > b->type) return 1;
+  if (a < b) return -1;
+  assert(a > b);
+  return 1;
+}
+
+static void po_join(grpc_exec_ctx *exec_ctx, polling_obj *a, polling_obj *b) {
+  switch (po_cmp(a, b)) {
+    case 0:
+      return;
+    case 1:
+      GPR_SWAP(polling_obj *, a, b);
+    /* fall through */
+    case -1:
+      gpr_mu_lock(&a->mu);
+      gpr_mu_lock(&b->mu);
+
+      if (a->group == NULL) {
+        if (b->group == NULL) {
+          polling_obj *initial_po[] = {a, b};
+          pg_create(exec_ctx, initial_po, GPR_ARRAY_SIZE(initial_po));
+          gpr_mu_unlock(&a->mu);
+          gpr_mu_unlock(&b->mu);
+        } else {
+          polling_group *b_group = pg_ref(b->group);
+          gpr_mu_unlock(&b->mu);
+          gpr_mu_unlock(&a->mu);
+          pg_join(exec_ctx, b_group, a);
+        }
+      } else if (b->group == NULL) {
+        polling_group *a_group = pg_ref(a->group);
+        gpr_mu_unlock(&a->mu);
+        gpr_mu_unlock(&b->mu);
+        pg_join(exec_ctx, a_group, b);
+      } else if (a->group == b->group) {
+        /* nothing to do */
+        gpr_mu_unlock(&a->mu);
+        gpr_mu_unlock(&b->mu);
+      } else {
+        polling_group *a_group = pg_ref(a->group);
+        polling_group *b_group = pg_ref(b->group);
+        gpr_mu_unlock(&a->mu);
+        gpr_mu_unlock(&b->mu);
+        pg_merge(exec_ctx, a_group, b_group);
+      }
+  }
+}
+
+static void pg_notify(grpc_exec_ctx *exec_ctx, polling_obj *a, polling_obj *b) {
+  if (a->type == PO_FD && b->type == PO_POLLSET) {
+    pollset_add_fd_locked(exec_ctx, (grpc_pollset *)b, (grpc_fd *)a, true);
+  } else if (a->type == PO_POLLSET && b->type == PO_FD) {
+    pollset_add_fd_locked(exec_ctx, (grpc_pollset *)a, (grpc_fd *)b, true);
+  }
+}
+
+static void pg_broadcast(grpc_exec_ctx *exec_ctx, polling_group *from,
+                         polling_group *to) {
+  for (polling_obj *a = from->po.next; a != &from->po; a = a->next) {
+    for (polling_obj *b = to->po.next; b != &to->po; b = b->next) {
+      if (po_cmp(a, b) < 0) {
+        gpr_mu_lock(&a->mu);
+        gpr_mu_lock(&b->mu);
+      } else {
+        GPR_ASSERT(po_cmp(a, b) != 0);
+        gpr_mu_lock(&b->mu);
+        gpr_mu_lock(&a->mu);
+      }
+      pg_notify(exec_ctx, a, b);
+      gpr_mu_unlock(&a->mu);
+      gpr_mu_unlock(&b->mu);
+    }
+  }
+}
+
+static void pg_create(grpc_exec_ctx *exec_ctx, polling_obj **initial_po,
+                      size_t initial_po_count) {
+  /* assumes all polling objects in initial_po are locked */
+  polling_group *pg = gpr_malloc(sizeof(*pg));
+  po_init(&pg->po, PO_POLLING_GROUP);
+  gpr_ref_init(&pg->refs, (int)initial_po_count);
+  for (size_t i = 0; i < initial_po_count; i++) {
+    GPR_ASSERT(initial_po[i]->group == NULL);
+    initial_po[i]->group = pg;
+  }
+  for (size_t i = 1; i < initial_po_count; i++) {
+    initial_po[i]->prev = initial_po[i - 1];
+  }
+  for (size_t i = 0; i < initial_po_count - 1; i++) {
+    initial_po[i]->next = initial_po[i + 1];
+  }
+  initial_po[0]->prev = &pg->po;
+  initial_po[initial_po_count - 1]->next = &pg->po;
+  pg->po.next = initial_po[0];
+  pg->po.prev = initial_po[initial_po_count - 1];
+  for (size_t i = 1; i < initial_po_count; i++) {
+    for (size_t j = 0; j < i; j++) {
+      pg_notify(exec_ctx, initial_po[i], initial_po[j]);
+    }
+  }
+}
+
+static void pg_join(grpc_exec_ctx *exec_ctx, polling_group *pg,
+                    polling_obj *po) {
+  /* assumes neither pg nor po are locked; consumes one ref to pg */
+  pg = pg_lock_latest(pg);
+  /* pg locked */
+  for (polling_obj *existing = pg->po.next /* skip pg - it's just a stub */;
+       existing != &pg->po; existing = existing->next) {
+    if (po_cmp(po, existing) < 0) {
+      gpr_mu_lock(&po->mu);
+      gpr_mu_lock(&existing->mu);
+    } else {
+      GPR_ASSERT(po_cmp(po, existing) != 0);
+      gpr_mu_lock(&existing->mu);
+      gpr_mu_lock(&po->mu);
+    }
+    /* pg, po, existing locked */
+    if (po->group != NULL) {
+      gpr_mu_unlock(&pg->po.mu);
+      polling_group *po_group = pg_ref(po->group);
+      gpr_mu_unlock(&po->mu);
+      gpr_mu_unlock(&existing->mu);
+      pg_merge(exec_ctx, pg, po_group);
+      /* early exit: polling obj picked up a group during joining: we needed
+         to do a full merge */
+      return;
+    }
+    pg_notify(exec_ctx, po, existing);
+    gpr_mu_unlock(&po->mu);
+    gpr_mu_unlock(&existing->mu);
+  }
+  gpr_mu_lock(&po->mu);
+  if (po->group != NULL) {
+    gpr_mu_unlock(&pg->po.mu);
+    polling_group *po_group = pg_ref(po->group);
+    gpr_mu_unlock(&po->mu);
+    pg_merge(exec_ctx, pg, po_group);
+    /* early exit: polling obj picked up a group during joining: we needed
+       to do a full merge */
+    return;
+  }
+  po->group = pg;
+  po->next = &pg->po;
+  po->prev = pg->po.prev;
+  po->prev->next = po->next->prev = po;
+  gpr_mu_unlock(&pg->po.mu);
+  gpr_mu_unlock(&po->mu);
+}
+
+static void pg_merge(grpc_exec_ctx *exec_ctx, polling_group *a,
+                     polling_group *b) {
+  for (;;) {
+    if (a == b) {
+      pg_unref(a);
+      pg_unref(b);
+      return;
+    }
+    if (a > b) GPR_SWAP(polling_group *, a, b);
+    gpr_mu_lock(&a->po.mu);
+    gpr_mu_lock(&b->po.mu);
+    if (a->po.group != NULL) {
+      polling_group *m2 = pg_ref(a->po.group);
+      gpr_mu_unlock(&a->po.mu);
+      gpr_mu_unlock(&b->po.mu);
+      pg_unref(a);
+      a = m2;
+    } else if (b->po.group != NULL) {
+      polling_group *m2 = pg_ref(b->po.group);
+      gpr_mu_unlock(&a->po.mu);
+      gpr_mu_unlock(&b->po.mu);
+      pg_unref(b);
+      b = m2;
+    } else {
+      break;
+    }
+  }
+  polling_group **unref = NULL;
+  size_t unref_count = 0;
+  size_t unref_cap = 0;
+  b->po.group = a;
+  pg_broadcast(exec_ctx, a, b);
+  pg_broadcast(exec_ctx, b, a);
+  while (b->po.next != &b->po) {
+    polling_obj *po = b->po.next;
+    gpr_mu_lock(&po->mu);
+    if (unref_count == unref_cap) {
+      unref_cap = GPR_MAX(8, 3 * unref_cap / 2);
+      unref = gpr_realloc(unref, unref_cap * sizeof(*unref));
+    }
+    unref[unref_count++] = po->group;
+    po->group = pg_ref(a);
+    // unlink from b
+    po->prev->next = po->next;
+    po->next->prev = po->prev;
+    // link to a
+    po->next = &a->po;
+    po->prev = a->po.prev;
+    po->next->prev = po->prev->next = po;
+    gpr_mu_unlock(&po->mu);
+  }
+  gpr_mu_unlock(&a->po.mu);
+  gpr_mu_unlock(&b->po.mu);
+  for (size_t i = 0; i < unref_count; i++) {
+    pg_unref(unref[i]);
+  }
+  gpr_free(unref);
+  pg_unref(b);
+}
+
+/*******************************************************************************
+ * Event engine binding
+ */
+
+static void shutdown_engine(void) {
+  fd_global_shutdown();
+  pollset_global_shutdown();
+}
+
+static const grpc_event_engine_vtable vtable = {
+    .pollset_size = sizeof(grpc_pollset),
+
+    .fd_create = fd_create,
+    .fd_wrapped_fd = fd_wrapped_fd,
+    .fd_orphan = fd_orphan,
+    .fd_shutdown = fd_shutdown,
+    .fd_is_shutdown = fd_is_shutdown,
+    .fd_notify_on_read = fd_notify_on_read,
+    .fd_notify_on_write = fd_notify_on_write,
+    .fd_get_read_notifier_pollset = fd_get_read_notifier_pollset,
+    .fd_get_workqueue = fd_get_workqueue,
+
+    .pollset_init = pollset_init,
+    .pollset_shutdown = pollset_shutdown,
+    .pollset_destroy = pollset_destroy,
+    .pollset_work = pollset_work,
+    .pollset_kick = pollset_kick,
+    .pollset_add_fd = pollset_add_fd,
+
+    .pollset_set_create = pollset_set_create,
+    .pollset_set_destroy = pollset_set_destroy,
+    .pollset_set_add_pollset = pollset_set_add_pollset,
+    .pollset_set_del_pollset = pollset_set_del_pollset,
+    .pollset_set_add_pollset_set = pollset_set_add_pollset_set,
+    .pollset_set_del_pollset_set = pollset_set_del_pollset_set,
+    .pollset_set_add_fd = pollset_set_add_fd,
+    .pollset_set_del_fd = pollset_set_del_fd,
+
+    .workqueue_ref = workqueue_ref,
+    .workqueue_unref = workqueue_unref,
+    .workqueue_scheduler = workqueue_scheduler,
+
+    .shutdown_engine = shutdown_engine,
+};
+
+const grpc_event_engine_vtable *grpc_init_epollex_linux(
+    bool explicitly_requested) {
+  if (!explicitly_requested) return NULL;
+
+  if (!grpc_has_wakeup_fd()) {
+    return NULL;
+  }
+
+  if (!grpc_is_epollexclusive_available()) {
+    return NULL;
+  }
+
+  fd_global_init();
+
+  if (!GRPC_LOG_IF_ERROR("pollset_global_init", pollset_global_init())) {
+    pollset_global_shutdown();
+    fd_global_shutdown();
+    return NULL;
+  }
+
+  return &vtable;
+}
+
+#else /* defined(GRPC_LINUX_EPOLL) */
+#if defined(GRPC_POSIX_SOCKET)
+#include "src/core/lib/iomgr/ev_posix.h"
+/* If GRPC_LINUX_EPOLL is not defined, it means epoll is not available. Return
+ * NULL */
+const grpc_event_engine_vtable *grpc_init_epollex_linux(
+    bool explicitly_requested) {
+  return NULL;
+}
+#endif /* defined(GRPC_POSIX_SOCKET) */
+
+#endif /* !defined(GRPC_LINUX_EPOLL) */
diff --git a/src/core/lib/iomgr/ev_epollex_linux.h b/src/core/lib/iomgr/ev_epollex_linux.h
new file mode 100644
index 0000000000..a078a7f19a
--- /dev/null
+++ b/src/core/lib/iomgr/ev_epollex_linux.h
@@ -0,0 +1,43 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_EV_EPOLLEX_LINUX_H
+#define GRPC_CORE_LIB_IOMGR_EV_EPOLLEX_LINUX_H
+
+#include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/iomgr/port.h"
+
+const grpc_event_engine_vtable *grpc_init_epollex_linux(
+    bool explicitly_requested);
+
+#endif /* GRPC_CORE_LIB_IOMGR_EV_EPOLLEX_LINUX_H */
diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epollsig_linux.c
index e603a75593..52362a62f4 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epollsig_linux.c
@@ -36,7 +36,7 @@
 /* This polling engine is only relevant on linux kernels supporting epoll() */
 #ifdef GRPC_LINUX_EPOLL
 
-#include "src/core/lib/iomgr/ev_epoll_linux.h"
+#include "src/core/lib/iomgr/ev_epollsig_linux.h"
 
 #include <assert.h>
 #include <errno.h>
@@ -63,11 +63,11 @@
 #include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/support/block_annotate.h"
 
-/* TODO: sreek - Move this to init.c and initialize this like other tracers. */
-static int grpc_polling_trace = 0; /* Disabled by default */
-#define GRPC_POLLING_TRACE(fmt, ...)       \
-  if (grpc_polling_trace) {                \
-    gpr_log(GPR_INFO, (fmt), __VA_ARGS__); \
+#define GRPC_POLLSET_KICK_BROADCAST ((grpc_pollset_worker *)1)
+
+#define GRPC_POLLING_TRACE(fmt, ...)        \
+  if (GRPC_TRACER_ON(grpc_polling_trace)) { \
+    gpr_log(GPR_INFO, (fmt), __VA_ARGS__);  \
   }
 
 /* Uncomment the following to enable extra checks on poll_object operations */
@@ -76,11 +76,6 @@ static int grpc_polling_trace = 0; /* Disabled by default */
 static int grpc_wakeup_signal = -1;
 static bool is_grpc_wakeup_signal_initialized = false;
 
-/* TODO: sreek: Right now, this wakes up all pollers. In future we should make
- * sure to wake up one polling thread (which can wake up other threads if
- * needed) */
-static grpc_wakeup_fd global_wakeup_fd;
-
 /* Implements the function defined in grpc_posix.h. This function might be
  * called before even calling grpc_init() to set either a different signal to
  * use. If signum == -1, then the use of signals is disabled */
@@ -454,8 +449,8 @@ static void polling_island_add_wakeup_fd_locked(polling_island *pi,
     gpr_asprintf(&err_msg,
                  "epoll_ctl (epoll_fd: %d) add wakeup fd: %d failed with "
                  "error: %d (%s)",
-                 pi->epoll_fd, GRPC_WAKEUP_FD_GET_READ_FD(&global_wakeup_fd),
-                 errno, strerror(errno));
+                 pi->epoll_fd, GRPC_WAKEUP_FD_GET_READ_FD(wakeup_fd), errno,
+                 strerror(errno));
     append_error(error, GRPC_OS_ERROR(errno, err_msg), err_desc);
     gpr_free(err_msg);
   }
@@ -558,7 +553,6 @@ static polling_island *polling_island_create(grpc_exec_ctx *exec_ctx,
     goto done;
   }
 
-  polling_island_add_wakeup_fd_locked(pi, &global_wakeup_fd, error);
   polling_island_add_wakeup_fd_locked(pi, &pi->workqueue_wakeup_fd, error);
 
   if (initial_fd != NULL) {
@@ -1116,11 +1110,10 @@ static grpc_error *pollset_global_init(void) {
   gpr_tls_init(&g_current_thread_pollset);
   gpr_tls_init(&g_current_thread_worker);
   poller_kick_init();
-  return grpc_wakeup_fd_init(&global_wakeup_fd);
+  return GRPC_ERROR_NONE;
 }
 
 static void pollset_global_shutdown(void) {
-  grpc_wakeup_fd_destroy(&global_wakeup_fd);
   gpr_tls_destroy(&g_current_thread_pollset);
   gpr_tls_destroy(&g_current_thread_worker);
 }
@@ -1226,10 +1219,6 @@ static grpc_error *pollset_kick(grpc_pollset *p,
   return error;
 }
 
-static grpc_error *kick_poller(void) {
-  return grpc_wakeup_fd_wakeup(&global_wakeup_fd);
-}
-
 static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
   gpr_mu_init(&pollset->po.mu);
   *mu = &pollset->po.mu;
@@ -1332,7 +1321,7 @@ static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
 /* pollset_shutdown is guaranteed to be called before pollset_destroy. So other
  * than destroying the mutexes, there is nothing special that needs to be done
  * here */
-static void pollset_destroy(grpc_pollset *pollset) {
+static void pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
   GPR_ASSERT(!pollset_has_workers(pollset));
   gpr_mu_destroy(&pollset->po.mu);
 }
@@ -1453,11 +1442,7 @@ static void pollset_work_and_unlock(grpc_exec_ctx *exec_ctx,
 
     for (int i = 0; i < ep_rv; ++i) {
       void *data_ptr = ep_ev[i].data.ptr;
-      if (data_ptr == &global_wakeup_fd) {
-        grpc_timer_consume_kick();
-        append_error(error, grpc_wakeup_fd_consume_wakeup(&global_wakeup_fd),
-                     err_desc);
-      } else if (data_ptr == &pi->workqueue_wakeup_fd) {
+      if (data_ptr == &pi->workqueue_wakeup_fd) {
         append_error(error,
                      grpc_wakeup_fd_consume_wakeup(&pi->workqueue_wakeup_fd),
                      err_desc);
@@ -1897,8 +1882,6 @@ static const grpc_event_engine_vtable vtable = {
     .pollset_set_add_fd = pollset_set_add_fd,
     .pollset_set_del_fd = pollset_set_del_fd,
 
-    .kick_poller = kick_poller,
-
     .workqueue_ref = workqueue_ref,
     .workqueue_unref = workqueue_unref,
     .workqueue_scheduler = workqueue_scheduler,
@@ -1921,7 +1904,8 @@ static bool is_epoll_available() {
   return true;
 }
 
-const grpc_event_engine_vtable *grpc_init_epoll_linux(void) {
+const grpc_event_engine_vtable *grpc_init_epollsig_linux(
+    bool explicit_request) {
   /* If use of signals is disabled, we cannot use epoll engine*/
   if (is_grpc_wakeup_signal_initialized && grpc_wakeup_signal < 0) {
     return NULL;
@@ -1936,7 +1920,13 @@ const grpc_event_engine_vtable *grpc_init_epoll_linux(void) {
   }
 
   if (!is_grpc_wakeup_signal_initialized) {
-    grpc_use_signal(SIGRTMIN + 6);
+    /* TODO(ctiller): when other epoll engines are ready, remove the true || to
+     * force this to be explitly chosen if needed */
+    if (true || explicit_request) {
+      grpc_use_signal(SIGRTMIN + 6);
+    } else {
+      return NULL;
+    }
   }
 
   fd_global_init();
@@ -1958,7 +1948,10 @@ const grpc_event_engine_vtable *grpc_init_epoll_linux(void) {
 #include "src/core/lib/iomgr/ev_posix.h"
 /* If GRPC_LINUX_EPOLL is not defined, it means epoll is not available. Return
  * NULL */
-const grpc_event_engine_vtable *grpc_init_epoll_linux(void) { return NULL; }
+const grpc_event_engine_vtable *grpc_init_epollsig_linux(
+    bool explicit_request) {
+  return NULL;
+}
 #endif /* defined(GRPC_POSIX_SOCKET) */
 
 void grpc_use_signal(int signum) {}
diff --git a/src/core/lib/iomgr/ev_epoll_linux.h b/src/core/lib/iomgr/ev_epollsig_linux.h
index 8fc3ff59a3..9e4034f2a7 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.h
+++ b/src/core/lib/iomgr/ev_epollsig_linux.h
@@ -31,13 +31,13 @@
  *
  */
 
-#ifndef GRPC_CORE_LIB_IOMGR_EV_EPOLL_LINUX_H
-#define GRPC_CORE_LIB_IOMGR_EV_EPOLL_LINUX_H
+#ifndef GRPC_CORE_LIB_IOMGR_EV_EPOLLSIG_LINUX_H
+#define GRPC_CORE_LIB_IOMGR_EV_EPOLLSIG_LINUX_H
 
 #include "src/core/lib/iomgr/ev_posix.h"
 #include "src/core/lib/iomgr/port.h"
 
-const grpc_event_engine_vtable *grpc_init_epoll_linux(void);
+const grpc_event_engine_vtable *grpc_init_epollsig_linux(bool explicit_request);
 
 #ifdef GRPC_LINUX_EPOLL
 void *grpc_fd_get_polling_island(grpc_fd *fd);
@@ -45,4 +45,4 @@ void *grpc_pollset_get_polling_island(grpc_pollset *ps);
 bool grpc_are_polling_islands_equal(void *p, void *q);
 #endif /* defined(GRPC_LINUX_EPOLL) */
 
-#endif /* GRPC_CORE_LIB_IOMGR_EV_EPOLL_LINUX_H */
+#endif /* GRPC_CORE_LIB_IOMGR_EV_EPOLLSIG_LINUX_H */
diff --git a/src/core/lib/iomgr/ev_poll_posix.c b/src/core/lib/iomgr/ev_poll_posix.c
index 9834cdd197..3a7648ac32 100644
--- a/src/core/lib/iomgr/ev_poll_posix.c
+++ b/src/core/lib/iomgr/ev_poll_posix.c
@@ -58,6 +58,8 @@
 #include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/support/block_annotate.h"
 
+#define GRPC_POLLSET_KICK_BROADCAST ((grpc_pollset_worker *)1)
+
 /*******************************************************************************
  * FD declarations
  */
@@ -122,8 +124,6 @@ struct grpc_fd {
   grpc_pollset *read_notifier_pollset;
 };
 
-static grpc_wakeup_fd global_wakeup_fd;
-
 /* Begin polling on an fd.
    Registers that the given pollset is interested in this fd - so that if read
    or writability interest changes, the pollset can be kicked to pick up that
@@ -784,19 +784,14 @@ static grpc_error *pollset_kick(grpc_pollset *p,
 static grpc_error *pollset_global_init(void) {
   gpr_tls_init(&g_current_thread_poller);
   gpr_tls_init(&g_current_thread_worker);
-  return grpc_wakeup_fd_init(&global_wakeup_fd);
+  return GRPC_ERROR_NONE;
 }
 
 static void pollset_global_shutdown(void) {
-  grpc_wakeup_fd_destroy(&global_wakeup_fd);
   gpr_tls_destroy(&g_current_thread_poller);
   gpr_tls_destroy(&g_current_thread_worker);
 }
 
-static grpc_error *kick_poller(void) {
-  return grpc_wakeup_fd_wakeup(&global_wakeup_fd);
-}
-
 /* main interface */
 
 static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
@@ -815,7 +810,7 @@ static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
   pollset->pollset_set_count = 0;
 }
 
-static void pollset_destroy(grpc_pollset *pollset) {
+static void pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
   GPR_ASSERT(!pollset_has_workers(pollset));
   GPR_ASSERT(pollset->idle_jobs.head == pollset->idle_jobs.tail);
   while (pollset->local_wakeup_cache) {
@@ -952,13 +947,10 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
       }
 
       fd_count = 0;
-      pfd_count = 2;
-      pfds[0].fd = GRPC_WAKEUP_FD_GET_READ_FD(&global_wakeup_fd);
+      pfd_count = 1;
+      pfds[0].fd = GRPC_WAKEUP_FD_GET_READ_FD(&worker.wakeup_fd->fd);
       pfds[0].events = POLLIN;
       pfds[0].revents = 0;
-      pfds[1].fd = GRPC_WAKEUP_FD_GET_READ_FD(&worker.wakeup_fd->fd);
-      pfds[1].events = POLLIN;
-      pfds[1].revents = 0;
       for (i = 0; i < pollset->fd_count; i++) {
         if (fd_is_orphaned(pollset->fds[i])) {
           GRPC_FD_UNREF(pollset->fds[i], "multipoller");
@@ -974,7 +966,7 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
       pollset->fd_count = fd_count;
       gpr_mu_unlock(&pollset->mu);
 
-      for (i = 2; i < pfd_count; i++) {
+      for (i = 1; i < pfd_count; i++) {
         grpc_fd *fd = watchers[i].fd;
         pfds[i].events = (short)fd_begin_poll(fd, pollset, &worker, POLLIN,
                                               POLLOUT, &watchers[i]);
@@ -992,7 +984,7 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
           work_combine_error(&error, GRPC_OS_ERROR(errno, "poll"));
         }
 
-        for (i = 2; i < pfd_count; i++) {
+        for (i = 1; i < pfd_count; i++) {
           if (watchers[i].fd == NULL) {
             fd_end_poll(exec_ctx, &watchers[i], 0, 0, NULL);
           } else {
@@ -1002,20 +994,15 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
           }
         }
       } else if (r == 0) {
-        for (i = 2; i < pfd_count; i++) {
+        for (i = 1; i < pfd_count; i++) {
           fd_end_poll(exec_ctx, &watchers[i], 0, 0, NULL);
         }
       } else {
         if (pfds[0].revents & POLLIN_CHECK) {
-          grpc_timer_consume_kick();
-          work_combine_error(&error,
-                             grpc_wakeup_fd_consume_wakeup(&global_wakeup_fd));
-        }
-        if (pfds[1].revents & POLLIN_CHECK) {
           work_combine_error(
               &error, grpc_wakeup_fd_consume_wakeup(&worker.wakeup_fd->fd));
         }
-        for (i = 2; i < pfd_count; i++) {
+        for (i = 1; i < pfd_count; i++) {
           if (watchers[i].fd == NULL) {
             fd_end_poll(exec_ctx, &watchers[i], 0, 0, NULL);
           } else {
@@ -1560,8 +1547,6 @@ static const grpc_event_engine_vtable vtable = {
     .pollset_set_add_fd = pollset_set_add_fd,
     .pollset_set_del_fd = pollset_set_del_fd,
 
-    .kick_poller = kick_poller,
-
     .workqueue_ref = workqueue_ref,
     .workqueue_unref = workqueue_unref,
     .workqueue_scheduler = workqueue_scheduler,
@@ -1569,7 +1554,7 @@ static const grpc_event_engine_vtable vtable = {
     .shutdown_engine = shutdown_engine,
 };
 
-const grpc_event_engine_vtable *grpc_init_poll_posix(void) {
+const grpc_event_engine_vtable *grpc_init_poll_posix(bool explicit_request) {
   if (!grpc_has_wakeup_fd()) {
     return NULL;
   }
@@ -1579,7 +1564,7 @@ const grpc_event_engine_vtable *grpc_init_poll_posix(void) {
   return &vtable;
 }
 
-const grpc_event_engine_vtable *grpc_init_poll_cv_posix(void) {
+const grpc_event_engine_vtable *grpc_init_poll_cv_posix(bool explicit_request) {
   global_cv_fd_table_init();
   grpc_enable_cv_wakeup_fds(1);
   if (!GRPC_LOG_IF_ERROR("pollset_global_init", pollset_global_init())) {
diff --git a/src/core/lib/iomgr/ev_poll_posix.h b/src/core/lib/iomgr/ev_poll_posix.h
index 202ffca14c..2890e93ead 100644
--- a/src/core/lib/iomgr/ev_poll_posix.h
+++ b/src/core/lib/iomgr/ev_poll_posix.h
@@ -36,7 +36,7 @@
 
 #include "src/core/lib/iomgr/ev_posix.h"
 
-const grpc_event_engine_vtable *grpc_init_poll_posix(void);
-const grpc_event_engine_vtable *grpc_init_poll_cv_posix(void);
+const grpc_event_engine_vtable *grpc_init_poll_posix(bool explicit_request);
+const grpc_event_engine_vtable *grpc_init_poll_cv_posix(bool explicit_request);
 
 #endif /* GRPC_CORE_LIB_IOMGR_EV_POLL_POSIX_H */
diff --git a/src/core/lib/iomgr/ev_posix.c b/src/core/lib/iomgr/ev_posix.c
index 13409a4de8..c4d2f23e29 100644
--- a/src/core/lib/iomgr/ev_posix.c
+++ b/src/core/lib/iomgr/ev_posix.c
@@ -44,10 +44,18 @@
 #include <grpc/support/string_util.h>
 #include <grpc/support/useful.h>
 
-#include "src/core/lib/iomgr/ev_epoll_linux.h"
+#include "src/core/lib/debug/trace.h"
+#include "src/core/lib/iomgr/ev_epoll1_linux.h"
+#include "src/core/lib/iomgr/ev_epoll_limited_pollers_linux.h"
+#include "src/core/lib/iomgr/ev_epoll_thread_pool_linux.h"
+#include "src/core/lib/iomgr/ev_epollex_linux.h"
+#include "src/core/lib/iomgr/ev_epollsig_linux.h"
 #include "src/core/lib/iomgr/ev_poll_posix.h"
 #include "src/core/lib/support/env.h"
 
+grpc_tracer_flag grpc_polling_trace =
+    GRPC_TRACER_INITIALIZER(false); /* Disabled by default */
+
 /** Default poll() function - a pointer so that it can be overridden by some
  *  tests */
 grpc_poll_function_type grpc_poll_function = poll;
@@ -57,7 +65,8 @@ grpc_wakeup_fd grpc_global_wakeup_fd;
 static const grpc_event_engine_vtable *g_event_engine;
 static const char *g_poll_strategy_name = NULL;
 
-typedef const grpc_event_engine_vtable *(*event_engine_factory_fn)(void);
+typedef const grpc_event_engine_vtable *(*event_engine_factory_fn)(
+    bool explicit_request);
 
 typedef struct {
   const char *name;
@@ -65,7 +74,11 @@ typedef struct {
 } event_engine_factory;
 
 static const event_engine_factory g_factories[] = {
-    {"epoll", grpc_init_epoll_linux},
+    {"epollex", grpc_init_epollex_linux},
+    {"epollsig", grpc_init_epollsig_linux},
+    {"epoll1", grpc_init_epoll1_linux},
+    {"epoll-threadpool", grpc_init_epoll_thread_pool_linux},
+    {"epoll-limited", grpc_init_epoll_limited_pollers_linux},
     {"poll", grpc_init_poll_posix},
     {"poll-cv", grpc_init_poll_cv_posix},
 };
@@ -102,7 +115,8 @@ static bool is(const char *want, const char *have) {
 static void try_engine(const char *engine) {
   for (size_t i = 0; i < GPR_ARRAY_SIZE(g_factories); i++) {
     if (is(engine, g_factories[i].name)) {
-      if ((g_event_engine = g_factories[i].factory())) {
+      if ((g_event_engine = g_factories[i].factory(
+               0 == strcmp(engine, g_factories[i].name)))) {
         g_poll_strategy_name = g_factories[i].name;
         gpr_log(GPR_DEBUG, "Using polling engine: %s", g_factories[i].name);
         return;
@@ -121,6 +135,8 @@ void grpc_set_event_engine_test_only(
 const char *grpc_get_poll_strategy_name() { return g_poll_strategy_name; }
 
 void grpc_event_engine_init(void) {
+  grpc_register_tracer("polling", &grpc_polling_trace);
+
   char *s = gpr_getenv("GRPC_POLL_STRATEGY");
   if (s == NULL) {
     s = gpr_strdup("all");
@@ -197,8 +213,8 @@ void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   g_event_engine->pollset_shutdown(exec_ctx, pollset, closure);
 }
 
-void grpc_pollset_destroy(grpc_pollset *pollset) {
-  g_event_engine->pollset_destroy(pollset);
+void grpc_pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
+  g_event_engine->pollset_destroy(exec_ctx, pollset);
 }
 
 grpc_error *grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
@@ -260,8 +276,6 @@ void grpc_pollset_set_del_fd(grpc_exec_ctx *exec_ctx,
   g_event_engine->pollset_set_del_fd(exec_ctx, pollset_set, fd);
 }
 
-grpc_error *grpc_kick_poller(void) { return g_event_engine->kick_poller(); }
-
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
 grpc_workqueue *grpc_workqueue_ref(grpc_workqueue *workqueue, const char *file,
                                    int line, const char *reason) {
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index becc4d359e..80619aab5f 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -36,12 +36,15 @@
 
 #include <poll.h>
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 #include "src/core/lib/iomgr/pollset.h"
 #include "src/core/lib/iomgr/pollset_set.h"
 #include "src/core/lib/iomgr/wakeup_fd_posix.h"
 #include "src/core/lib/iomgr/workqueue.h"
 
+extern grpc_tracer_flag grpc_polling_trace; /* Disabled by default */
+
 typedef struct grpc_fd grpc_fd;
 
 typedef struct grpc_event_engine_vtable {
@@ -64,7 +67,7 @@ typedef struct grpc_event_engine_vtable {
   void (*pollset_init)(grpc_pollset *pollset, gpr_mu **mu);
   void (*pollset_shutdown)(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                            grpc_closure *closure);
-  void (*pollset_destroy)(grpc_pollset *pollset);
+  void (*pollset_destroy)(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset);
   grpc_error *(*pollset_work)(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                               grpc_pollset_worker **worker, gpr_timespec now,
                               gpr_timespec deadline);
@@ -93,8 +96,6 @@ typedef struct grpc_event_engine_vtable {
   void (*pollset_set_del_fd)(grpc_exec_ctx *exec_ctx,
                              grpc_pollset_set *pollset_set, grpc_fd *fd);
 
-  grpc_error *(*kick_poller)(void);
-
   void (*shutdown_engine)(void);
 
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
diff --git a/src/core/lib/iomgr/exec_ctx.c b/src/core/lib/iomgr/exec_ctx.c
index 2532a708e7..318bb2b713 100644
--- a/src/core/lib/iomgr/exec_ctx.c
+++ b/src/core/lib/iomgr/exec_ctx.c
@@ -62,6 +62,11 @@ bool grpc_always_ready_to_finish(grpc_exec_ctx *exec_ctx, void *arg_ignored) {
   return true;
 }
 
+bool grpc_exec_ctx_has_work(grpc_exec_ctx *exec_ctx) {
+  return exec_ctx->active_combiner != NULL ||
+         !grpc_closure_list_empty(exec_ctx->closure_list);
+}
+
 bool grpc_exec_ctx_flush(grpc_exec_ctx *exec_ctx) {
   bool did_something = 0;
   GPR_TIMER_BEGIN("grpc_exec_ctx_flush", 0);
diff --git a/src/core/lib/iomgr/exec_ctx.h b/src/core/lib/iomgr/exec_ctx.h
index f99a0fee5f..759a3ae2d5 100644
--- a/src/core/lib/iomgr/exec_ctx.h
+++ b/src/core/lib/iomgr/exec_ctx.h
@@ -93,6 +93,8 @@ struct grpc_exec_ctx {
 
 extern grpc_closure_scheduler *grpc_schedule_on_exec_ctx;
 
+bool grpc_exec_ctx_has_work(grpc_exec_ctx *exec_ctx);
+
 /** Flush any work that has been enqueued onto this grpc_exec_ctx.
  *  Caller must guarantee that no interfering locks are held.
  *  Returns true if work was performed, false otherwise. */
diff --git a/src/core/lib/iomgr/iomgr.c b/src/core/lib/iomgr/iomgr.c
index 001e528409..1fd41c2f88 100644
--- a/src/core/lib/iomgr/iomgr.c
+++ b/src/core/lib/iomgr/iomgr.c
@@ -47,6 +47,7 @@
 #include "src/core/lib/iomgr/iomgr_internal.h"
 #include "src/core/lib/iomgr/network_status_tracker.h"
 #include "src/core/lib/iomgr/timer.h"
+#include "src/core/lib/iomgr/timer_manager.h"
 #include "src/core/lib/support/env.h"
 #include "src/core/lib/support/string.h"
 
@@ -67,6 +68,8 @@ void grpc_iomgr_init(void) {
   grpc_iomgr_platform_init();
 }
 
+void grpc_iomgr_start(void) { grpc_timer_manager_init(); }
+
 static size_t count_objects(void) {
   grpc_iomgr_object *obj;
   size_t n = 0;
@@ -88,6 +91,7 @@ void grpc_iomgr_shutdown(grpc_exec_ctx *exec_ctx) {
       gpr_now(GPR_CLOCK_REALTIME), gpr_time_from_seconds(10, GPR_TIMESPAN));
   gpr_timespec last_warning_time = gpr_now(GPR_CLOCK_REALTIME);
 
+  grpc_timer_manager_shutdown();
   grpc_iomgr_platform_flush();
 
   gpr_mu_lock(&g_mu);
diff --git a/src/core/lib/iomgr/iomgr.h b/src/core/lib/iomgr/iomgr.h
index 245a1e08aa..6e2e023615 100644
--- a/src/core/lib/iomgr/iomgr.h
+++ b/src/core/lib/iomgr/iomgr.h
@@ -40,6 +40,9 @@
 /** Initializes the iomgr. */
 void grpc_iomgr_init(void);
 
+/** Starts any background threads for iomgr. */
+void grpc_iomgr_start(void);
+
 /** Signals the intention to shutdown the iomgr. Expects to be able to flush
  * exec_ctx. */
 void grpc_iomgr_shutdown(grpc_exec_ctx *exec_ctx);
diff --git a/src/core/lib/iomgr/is_epollexclusive_available.c b/src/core/lib/iomgr/is_epollexclusive_available.c
new file mode 100644
index 0000000000..34fcf313e5
--- /dev/null
+++ b/src/core/lib/iomgr/is_epollexclusive_available.c
@@ -0,0 +1,116 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/port.h"
+
+#include "src/core/lib/iomgr/is_epollexclusive_available.h"
+
+#ifdef GRPC_LINUX_EPOLL
+
+#include <grpc/support/log.h>
+
+#include <errno.h>
+#include <sys/eventfd.h>
+#include <unistd.h>
+
+#include "src/core/lib/iomgr/sys_epoll_wrapper.h"
+
+/* This polling engine is only relevant on linux kernels supporting epoll() */
+bool grpc_is_epollexclusive_available(void) {
+  static bool logged_why_not = false;
+
+  int fd = epoll_create1(EPOLL_CLOEXEC);
+  if (fd < 0) {
+    if (!logged_why_not) {
+      gpr_log(GPR_ERROR,
+              "epoll_create1 failed with error: %d. Not using epollex polling "
+              "engine.",
+              fd);
+      logged_why_not = true;
+    }
+    return false;
+  }
+  int evfd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
+  if (evfd < 0) {
+    if (!logged_why_not) {
+      gpr_log(GPR_ERROR,
+              "eventfd failed with error: %d. Not using epollex polling "
+              "engine.",
+              fd);
+      logged_why_not = true;
+    }
+    close(fd);
+    return false;
+  }
+  struct epoll_event ev = {
+      /* choose events that should cause an error on
+         EPOLLEXCLUSIVE enabled kernels - specifically the combination of
+         EPOLLONESHOT and EPOLLEXCLUSIVE */
+      .events = (uint32_t)(EPOLLET | EPOLLIN | EPOLLEXCLUSIVE | EPOLLONESHOT),
+      .data.ptr = NULL};
+  if (epoll_ctl(fd, EPOLL_CTL_ADD, evfd, &ev) != 0) {
+    if (errno != EINVAL) {
+      if (!logged_why_not) {
+        gpr_log(
+            GPR_ERROR,
+            "epoll_ctl with EPOLLEXCLUSIVE | EPOLLONESHOT failed with error: "
+            "%d. Not using epollex polling engine.",
+            errno);
+        logged_why_not = true;
+      }
+      close(fd);
+      close(evfd);
+      return false;
+    }
+  } else {
+    if (!logged_why_not) {
+      gpr_log(GPR_ERROR,
+              "epoll_ctl with EPOLLEXCLUSIVE | EPOLLONESHOT succeeded. This is "
+              "evidence of no EPOLLEXCLUSIVE support. Not using "
+              "epollex polling engine.");
+      logged_why_not = true;
+    }
+    close(fd);
+    close(evfd);
+    return false;
+  }
+  close(evfd);
+  close(fd);
+  return true;
+}
+
+#else
+
+bool grpc_is_epollexclusive_available(void) { return false; }
+
+#endif
diff --git a/src/core/lib/iomgr/is_epollexclusive_available.h b/src/core/lib/iomgr/is_epollexclusive_available.h
new file mode 100644
index 0000000000..b65b819e74
--- /dev/null
+++ b/src/core/lib/iomgr/is_epollexclusive_available.h
@@ -0,0 +1,41 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_IS_EPOLLEXCLUSIVE_AVAILABLE_H
+#define GRPC_CORE_LIB_IOMGR_IS_EPOLLEXCLUSIVE_AVAILABLE_H
+
+#include <stdbool.h>
+
+bool grpc_is_epollexclusive_available(void);
+
+#endif /* GRPC_CORE_LIB_IOMGR_IS_EPOLLEXCLUSIVE_AVAILABLE_H */
diff --git a/src/core/lib/iomgr/lockfree_event.c b/src/core/lib/iomgr/lockfree_event.c
index 17e3bbf727..898ec1cb1b 100644
--- a/src/core/lib/iomgr/lockfree_event.c
+++ b/src/core/lib/iomgr/lockfree_event.c
@@ -35,6 +35,10 @@
 
 #include <grpc/support/log.h>
 
+#include "src/core/lib/debug/trace.h"
+
+extern grpc_tracer_flag grpc_polling_trace;
+
 /* 'state' holds the to call when the fd is readable or writable respectively.
    It can contain one of the following values:
      CLOSURE_READY     : The fd has an I/O event of interest but there is no
@@ -93,6 +97,10 @@ void grpc_lfev_notify_on(grpc_exec_ctx *exec_ctx, gpr_atm *state,
                          grpc_closure *closure) {
   while (true) {
     gpr_atm curr = gpr_atm_no_barrier_load(state);
+    if (GRPC_TRACER_ON(grpc_polling_trace)) {
+      gpr_log(GPR_DEBUG, "lfev_notify_on: %p curr=%p closure=%p", state,
+              (void *)curr, closure);
+    }
     switch (curr) {
       case CLOSURE_NOT_READY: {
         /* CLOSURE_NOT_READY -> <closure>.
@@ -155,6 +163,10 @@ bool grpc_lfev_set_shutdown(grpc_exec_ctx *exec_ctx, gpr_atm *state,
 
   while (true) {
     gpr_atm curr = gpr_atm_no_barrier_load(state);
+    if (GRPC_TRACER_ON(grpc_polling_trace)) {
+      gpr_log(GPR_DEBUG, "lfev_set_shutdown: %p curr=%p err=%s", state,
+              (void *)curr, grpc_error_string(shutdown_err));
+    }
     switch (curr) {
       case CLOSURE_READY:
       case CLOSURE_NOT_READY:
@@ -200,6 +212,10 @@ void grpc_lfev_set_ready(grpc_exec_ctx *exec_ctx, gpr_atm *state) {
   while (true) {
     gpr_atm curr = gpr_atm_no_barrier_load(state);
 
+    if (GRPC_TRACER_ON(grpc_polling_trace)) {
+      gpr_log(GPR_DEBUG, "lfev_set_ready: %p curr=%p", state, (void *)curr);
+    }
+
     switch (curr) {
       case CLOSURE_READY: {
         /* Already ready. We are done here */
diff --git a/src/core/lib/iomgr/pollset.h b/src/core/lib/iomgr/pollset.h
index 9bf3cdac89..69e20098d7 100644
--- a/src/core/lib/iomgr/pollset.h
+++ b/src/core/lib/iomgr/pollset.h
@@ -40,8 +40,6 @@
 
 #include "src/core/lib/iomgr/exec_ctx.h"
 
-#define GRPC_POLLSET_KICK_BROADCAST ((grpc_pollset_worker *)1)
-
 /* A grpc_pollset is a set of file descriptors that a higher level item is
    interested in. For example:
     - a server will typically keep a pollset containing all connected channels,
@@ -59,7 +57,7 @@ void grpc_pollset_init(grpc_pollset *pollset, gpr_mu **mu);
  * pollset's mutex must be held */
 void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                            grpc_closure *closure);
-void grpc_pollset_destroy(grpc_pollset *pollset);
+void grpc_pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset);
 
 /* Do some work on a pollset.
    May involve invoking asynchronous callbacks, or actually polling file
@@ -88,8 +86,7 @@ grpc_error *grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                               gpr_timespec deadline) GRPC_MUST_USE_RESULT;
 
 /* Break one polling thread out of polling work for this pollset.
-   If specific_worker is GRPC_POLLSET_KICK_BROADCAST, kick ALL the workers.
-   Otherwise, if specific_worker is non-NULL, then kick that worker. */
+   If specific_worker is non-NULL, then kick that worker. */
 grpc_error *grpc_pollset_kick(grpc_pollset *pollset,
                               grpc_pollset_worker *specific_worker)
     GRPC_MUST_USE_RESULT;
diff --git a/src/core/lib/iomgr/pollset_uv.c b/src/core/lib/iomgr/pollset_uv.c
index a2f81bcd78..5923da98e2 100644
--- a/src/core/lib/iomgr/pollset_uv.c
+++ b/src/core/lib/iomgr/pollset_uv.c
@@ -106,7 +106,7 @@ void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_NONE);
 }
 
-void grpc_pollset_destroy(grpc_pollset *pollset) {
+void grpc_pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
   uv_close((uv_handle_t *)&pollset->timer, timer_close_cb);
   // timer.data is a boolean indicating that the timer has finished closing
   pollset->timer.data = (void *)0;
diff --git a/src/core/lib/iomgr/pollset_windows.c b/src/core/lib/iomgr/pollset_windows.c
index 04c6b71747..b5f454cfa9 100644
--- a/src/core/lib/iomgr/pollset_windows.c
+++ b/src/core/lib/iomgr/pollset_windows.c
@@ -43,6 +43,8 @@
 #include "src/core/lib/iomgr/pollset.h"
 #include "src/core/lib/iomgr/pollset_windows.h"
 
+#define GRPC_POLLSET_KICK_BROADCAST ((grpc_pollset_worker *)1)
+
 gpr_mu grpc_polling_mu;
 static grpc_pollset_worker *g_active_poller;
 static grpc_pollset_worker g_global_root_worker;
@@ -114,7 +116,7 @@ void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   }
 }
 
-void grpc_pollset_destroy(grpc_pollset *pollset) {}
+void grpc_pollset_destroy(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {}
 
 grpc_error *grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                               grpc_pollset_worker **worker_hdl,
@@ -227,6 +229,4 @@ grpc_error *grpc_pollset_kick(grpc_pollset *p,
   return GRPC_ERROR_NONE;
 }
 
-void grpc_kick_poller(void) { grpc_iocp_kick(); }
-
 #endif /* GRPC_WINSOCK_SOCKET */
diff --git a/src/core/lib/iomgr/port.h b/src/core/lib/iomgr/port.h
index 269dc35003..2a553f4114 100644
--- a/src/core/lib/iomgr/port.h
+++ b/src/core/lib/iomgr/port.h
@@ -88,6 +88,7 @@
 #ifndef __GLIBC__
 #define GRPC_LINUX_EPOLL 1
 #define GRPC_LINUX_EVENTFD 1
+#define GRPC_MSG_IOVLEN_TYPE int
 #endif
 #ifndef GRPC_LINUX_EVENTFD
 #define GRPC_POSIX_NO_SPECIAL_WAKEUP_FD 1
diff --git a/src/core/lib/iomgr/resource_quota.c b/src/core/lib/iomgr/resource_quota.c
index c3ee878651..6b2b85cce0 100644
--- a/src/core/lib/iomgr/resource_quota.c
+++ b/src/core/lib/iomgr/resource_quota.c
@@ -44,7 +44,7 @@
 
 #include "src/core/lib/iomgr/combiner.h"
 
-int grpc_resource_quota_trace = 0;
+grpc_tracer_flag grpc_resource_quota_trace = GRPC_TRACER_INITIALIZER(false);
 
 #define MEMORY_USAGE_ESTIMATION_MAX 65536
 
@@ -307,13 +307,14 @@ static bool rq_alloc(grpc_exec_ctx *exec_ctx,
       resource_user->free_pool = 0;
       resource_quota->free_pool -= amt;
       rq_update_estimate(resource_quota);
-      if (grpc_resource_quota_trace) {
+      if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
         gpr_log(GPR_DEBUG, "RQ %s %s: grant alloc %" PRId64
                            " bytes; rq_free_pool -> %" PRId64,
                 resource_quota->name, resource_user->name, amt,
                 resource_quota->free_pool);
       }
-    } else if (grpc_resource_quota_trace && resource_user->free_pool >= 0) {
+    } else if (GRPC_TRACER_ON(grpc_resource_quota_trace) &&
+               resource_user->free_pool >= 0) {
       gpr_log(GPR_DEBUG, "RQ %s %s: discard already satisfied alloc request",
               resource_quota->name, resource_user->name);
     }
@@ -342,7 +343,7 @@ static bool rq_reclaim_from_per_user_free_pool(
       resource_user->free_pool = 0;
       resource_quota->free_pool += amt;
       rq_update_estimate(resource_quota);
-      if (grpc_resource_quota_trace) {
+      if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
         gpr_log(GPR_DEBUG, "RQ %s %s: reclaim_from_per_user_free_pool %" PRId64
                            " bytes; rq_free_pool -> %" PRId64,
                 resource_quota->name, resource_user->name, amt,
@@ -365,7 +366,7 @@ static bool rq_reclaim(grpc_exec_ctx *exec_ctx,
                                  : GRPC_RULIST_RECLAIMER_BENIGN;
   grpc_resource_user *resource_user = rulist_pop_head(resource_quota, list);
   if (resource_user == NULL) return false;
-  if (grpc_resource_quota_trace) {
+  if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
     gpr_log(GPR_DEBUG, "RQ %s %s: initiate %s reclamation",
             resource_quota->name, resource_user->name,
             destructive ? "destructive" : "benign");
@@ -786,7 +787,7 @@ void grpc_resource_user_alloc(grpc_exec_ctx *exec_ctx,
   gpr_mu_lock(&resource_user->mu);
   ru_ref_by(resource_user, (gpr_atm)size);
   resource_user->free_pool -= (int64_t)size;
-  if (grpc_resource_quota_trace) {
+  if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
     gpr_log(GPR_DEBUG, "RQ %s %s: alloc %" PRIdPTR "; free_pool -> %" PRId64,
             resource_user->resource_quota->name, resource_user->name, size,
             resource_user->free_pool);
@@ -810,7 +811,7 @@ void grpc_resource_user_free(grpc_exec_ctx *exec_ctx,
   gpr_mu_lock(&resource_user->mu);
   bool was_zero_or_negative = resource_user->free_pool <= 0;
   resource_user->free_pool += (int64_t)size;
-  if (grpc_resource_quota_trace) {
+  if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
     gpr_log(GPR_DEBUG, "RQ %s %s: free %" PRIdPTR "; free_pool -> %" PRId64,
             resource_user->resource_quota->name, resource_user->name, size,
             resource_user->free_pool);
@@ -839,7 +840,7 @@ void grpc_resource_user_post_reclaimer(grpc_exec_ctx *exec_ctx,
 
 void grpc_resource_user_finish_reclamation(grpc_exec_ctx *exec_ctx,
                                            grpc_resource_user *resource_user) {
-  if (grpc_resource_quota_trace) {
+  if (GRPC_TRACER_ON(grpc_resource_quota_trace)) {
     gpr_log(GPR_DEBUG, "RQ %s %s: reclamation complete",
             resource_user->resource_quota->name, resource_user->name);
   }
diff --git a/src/core/lib/iomgr/resource_quota.h b/src/core/lib/iomgr/resource_quota.h
index 6f99be0d51..51122dad01 100644
--- a/src/core/lib/iomgr/resource_quota.h
+++ b/src/core/lib/iomgr/resource_quota.h
@@ -36,6 +36,7 @@
 
 #include <grpc/grpc.h>
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 
 /** \file Tracks resource usage against a pool.
@@ -75,7 +76,7 @@
     maintain lists of users (which users arrange to leave before they are
     destroyed) */
 
-extern int grpc_resource_quota_trace;
+extern grpc_tracer_flag grpc_resource_quota_trace;
 
 grpc_resource_quota *grpc_resource_quota_ref_internal(
     grpc_resource_quota *resource_quota);
diff --git a/src/core/lib/iomgr/sys_epoll_wrapper.h b/src/core/lib/iomgr/sys_epoll_wrapper.h
new file mode 100644
index 0000000000..2f08423193
--- /dev/null
+++ b/src/core/lib/iomgr/sys_epoll_wrapper.h
@@ -0,0 +1,43 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_SYS_EPOLL_WRAPPER_H
+#define GRPC_CORE_LIB_IOMGR_SYS_EPOLL_WRAPPER_H
+
+#include <sys/epoll.h>
+
+#ifndef EPOLLEXCLUSIVE
+#define EPOLLEXCLUSIVE (1 << 28)
+#endif
+
+#endif /* GRPC_CORE_LIB_IOMGR_SYS_EPOLL_WRAPPER_H */
diff --git a/src/core/lib/iomgr/tcp_client_posix.c b/src/core/lib/iomgr/tcp_client_posix.c
index a2692707d9..5c7da999e0 100644
--- a/src/core/lib/iomgr/tcp_client_posix.c
+++ b/src/core/lib/iomgr/tcp_client_posix.c
@@ -58,7 +58,7 @@
 #include "src/core/lib/iomgr/unix_sockets_posix.h"
 #include "src/core/lib/support/string.h"
 
-extern int grpc_tcp_trace;
+extern grpc_tracer_flag grpc_tcp_trace;
 
 typedef struct {
   gpr_mu mu;
@@ -114,7 +114,7 @@ done:
 static void tc_on_alarm(grpc_exec_ctx *exec_ctx, void *acp, grpc_error *error) {
   int done;
   async_connect *ac = acp;
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     const char *str = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: on_alarm: error=%s", ac->addr_str,
             str);
@@ -152,7 +152,7 @@ static void on_writable(grpc_exec_ctx *exec_ctx, void *acp, grpc_error *error) {
 
   GRPC_ERROR_REF(error);
 
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     const char *str = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: on_writable: error=%s",
             ac->addr_str, str);
@@ -330,9 +330,9 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
                     grpc_schedule_on_exec_ctx);
   ac->channel_args = grpc_channel_args_copy(channel_args);
 
-  if (grpc_tcp_trace) {
-    gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: asynchronously connecting",
-            ac->addr_str);
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
+    gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: asynchronously connecting fd %p",
+            ac->addr_str, fdobj);
   }
 
   gpr_mu_lock(&ac->mu);
diff --git a/src/core/lib/iomgr/tcp_client_uv.c b/src/core/lib/iomgr/tcp_client_uv.c
index 682c24ed56..f0856a76d4 100644
--- a/src/core/lib/iomgr/tcp_client_uv.c
+++ b/src/core/lib/iomgr/tcp_client_uv.c
@@ -46,7 +46,7 @@
 #include "src/core/lib/iomgr/tcp_uv.h"
 #include "src/core/lib/iomgr/timer.h"
 
-extern int grpc_tcp_trace;
+extern grpc_tracer_flag grpc_tcp_trace;
 
 typedef struct grpc_uv_tcp_connect {
   uv_connect_t connect_req;
@@ -72,7 +72,7 @@ static void uv_tc_on_alarm(grpc_exec_ctx *exec_ctx, void *acp,
                            grpc_error *error) {
   int done;
   grpc_uv_tcp_connect *connect = acp;
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     const char *str = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: on_alarm: error=%s",
             connect->addr_name, str);
@@ -156,7 +156,7 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
   uv_tcp_init(uv_default_loop(), connect->tcp_handle);
   connect->connect_req.data = connect;
 
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: asynchronously connecting",
             connect->addr_name);
   }
diff --git a/src/core/lib/iomgr/tcp_posix.c b/src/core/lib/iomgr/tcp_posix.c
index 5f4b38de2b..5d360b0b80 100644
--- a/src/core/lib/iomgr/tcp_posix.c
+++ b/src/core/lib/iomgr/tcp_posix.c
@@ -74,7 +74,7 @@ typedef GRPC_MSG_IOVLEN_TYPE msg_iovlen_type;
 typedef size_t msg_iovlen_type;
 #endif
 
-int grpc_tcp_trace = 0;
+grpc_tracer_flag grpc_tcp_trace = GRPC_TRACER_INITIALIZER(false);
 
 typedef struct {
   grpc_endpoint base;
@@ -221,7 +221,7 @@ static void call_read_cb(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp,
                          grpc_error *error) {
   grpc_closure *cb = tcp->read_cb;
 
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     size_t i;
     const char *str = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "read: error=%s", str);
@@ -468,14 +468,14 @@ static void tcp_handle_write(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
   }
 
   if (!tcp_flush(tcp, &error)) {
-    if (grpc_tcp_trace) {
+    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
       gpr_log(GPR_DEBUG, "write: delayed");
     }
     grpc_fd_notify_on_write(exec_ctx, tcp->em_fd, &tcp->write_closure);
   } else {
     cb = tcp->write_cb;
     tcp->write_cb = NULL;
-    if (grpc_tcp_trace) {
+    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
       const char *str = grpc_error_string(error);
       gpr_log(GPR_DEBUG, "write: %s", str);
     }
@@ -490,7 +490,7 @@ static void tcp_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   grpc_tcp *tcp = (grpc_tcp *)ep;
   grpc_error *error = GRPC_ERROR_NONE;
 
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     size_t i;
 
     for (i = 0; i < buf->count; i++) {
@@ -521,12 +521,12 @@ static void tcp_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   if (!tcp_flush(tcp, &error)) {
     TCP_REF(tcp, "write");
     tcp->write_cb = cb;
-    if (grpc_tcp_trace) {
+    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
       gpr_log(GPR_DEBUG, "write: delayed");
     }
     grpc_fd_notify_on_write(exec_ctx, tcp->em_fd, &tcp->write_closure);
   } else {
-    if (grpc_tcp_trace) {
+    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
       const char *str = grpc_error_string(error);
       gpr_log(GPR_DEBUG, "write: %s", str);
     }
diff --git a/src/core/lib/iomgr/tcp_posix.h b/src/core/lib/iomgr/tcp_posix.h
index 1ad5788331..4ad60c116e 100644
--- a/src/core/lib/iomgr/tcp_posix.h
+++ b/src/core/lib/iomgr/tcp_posix.h
@@ -44,10 +44,11 @@
    otherwise specified.
 */
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/endpoint.h"
 #include "src/core/lib/iomgr/ev_posix.h"
 
-extern int grpc_tcp_trace;
+extern grpc_tracer_flag grpc_tcp_trace;
 
 /* Create a tcp endpoint given a file desciptor and a read slice size.
    Takes ownership of fd. */
diff --git a/src/core/lib/iomgr/tcp_server_posix.c b/src/core/lib/iomgr/tcp_server_posix.c
index e66ffc9b1c..08997b5e2b 100644
--- a/src/core/lib/iomgr/tcp_server_posix.c
+++ b/src/core/lib/iomgr/tcp_server_posix.c
@@ -257,7 +257,7 @@ static void on_read(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *err) {
     addr_str = grpc_sockaddr_to_uri(&addr);
     gpr_asprintf(&name, "tcp-server-connection:%s", addr_str);
 
-    if (grpc_tcp_trace) {
+    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
       gpr_log(GPR_DEBUG, "SERVER_CONNECT: incoming connection: %s", addr_str);
     }
 
diff --git a/src/core/lib/iomgr/tcp_uv.c b/src/core/lib/iomgr/tcp_uv.c
index 8e8db9f7b4..e7157537f6 100644
--- a/src/core/lib/iomgr/tcp_uv.c
+++ b/src/core/lib/iomgr/tcp_uv.c
@@ -52,7 +52,7 @@
 #include "src/core/lib/slice/slice_string_helpers.h"
 #include "src/core/lib/support/string.h"
 
-int grpc_tcp_trace = 0;
+grpc_tracer_flag grpc_tcp_trace = GRPC_TRACER_INITIALIZER(false);
 
 typedef struct {
   grpc_endpoint base;
@@ -158,7 +158,7 @@ static void read_callback(uv_stream_t *stream, ssize_t nread,
     sub = grpc_slice_sub_no_ref(tcp->read_slice, 0, (size_t)nread);
     grpc_slice_buffer_add(tcp->read_slices, sub);
     error = GRPC_ERROR_NONE;
-    if (grpc_tcp_trace) {
+    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
       size_t i;
       const char *str = grpc_error_string(error);
       gpr_log(GPR_DEBUG, "read: error=%s", str);
@@ -199,7 +199,7 @@ static void uv_endpoint_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                            grpc_slice_from_static_string(uv_strerror(status)));
     grpc_closure_sched(exec_ctx, cb, error);
   }
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     const char *str = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "Initiating read on %p: error=%s", tcp, str);
   }
@@ -217,7 +217,7 @@ static void write_callback(uv_write_t *req, int status) {
   } else {
     error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("TCP Write failed");
   }
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     const char *str = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "write complete on %p: error=%s", tcp, str);
   }
@@ -238,7 +238,7 @@ static void uv_endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   grpc_slice *slice;
   uv_write_t *write_req;
 
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     size_t j;
 
     for (j = 0; j < write_slices->count; j++) {
@@ -346,7 +346,7 @@ grpc_endpoint *grpc_tcp_create(uv_tcp_t *handle,
                                char *peer_string) {
   grpc_tcp *tcp = (grpc_tcp *)gpr_malloc(sizeof(grpc_tcp));
 
-  if (grpc_tcp_trace) {
+  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
     gpr_log(GPR_DEBUG, "Creating TCP endpoint %p", tcp);
   }
 
diff --git a/src/core/lib/iomgr/tcp_uv.h b/src/core/lib/iomgr/tcp_uv.h
index 970fcafe4a..106bec5eca 100644
--- a/src/core/lib/iomgr/tcp_uv.h
+++ b/src/core/lib/iomgr/tcp_uv.h
@@ -44,11 +44,12 @@
    otherwise specified.
 */
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/endpoint.h"
 
 #include <uv.h>
 
-extern int grpc_tcp_trace;
+extern grpc_tracer_flag grpc_tcp_trace;
 
 #define GRPC_TCP_DEFAULT_READ_SLICE_SIZE 8192
 
diff --git a/src/core/lib/iomgr/timer_generic.c b/src/core/lib/iomgr/timer_generic.c
index d8e6068431..b28340b71c 100644
--- a/src/core/lib/iomgr/timer_generic.c
+++ b/src/core/lib/iomgr/timer_generic.c
@@ -56,8 +56,8 @@
 #define MIN_QUEUE_WINDOW_DURATION 0.01
 #define MAX_QUEUE_WINDOW_DURATION 1
 
-int grpc_timer_trace = 0;
-int grpc_timer_check_trace = 0;
+grpc_tracer_flag grpc_timer_trace = GRPC_TRACER_INITIALIZER(false);
+grpc_tracer_flag grpc_timer_check_trace = GRPC_TRACER_INITIALIZER(false);
 
 typedef struct {
   gpr_mu mu;
@@ -232,14 +232,13 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
   GPR_ASSERT(deadline.clock_type == g_clock_type);
   GPR_ASSERT(now.clock_type == g_clock_type);
   timer->closure = closure;
-  timer->deadline = timespec_to_atm_round_up(deadline);
+  gpr_atm deadline_atm = timer->deadline = timespec_to_atm_round_up(deadline);
 
-  if (grpc_timer_trace) {
+  if (GRPC_TRACER_ON(grpc_timer_trace)) {
     gpr_log(GPR_DEBUG, "TIMER %p: SET %" PRId64 ".%09d [%" PRIdPTR
                        "] now %" PRId64 ".%09d [%" PRIdPTR "] call %p[%p]",
-            timer, deadline.tv_sec, deadline.tv_nsec, timer->deadline,
-            now.tv_sec, now.tv_nsec, timespec_to_atm_round_down(now), closure,
-            closure->cb);
+            timer, deadline.tv_sec, deadline.tv_nsec, deadline_atm, now.tv_sec,
+            now.tv_nsec, timespec_to_atm_round_down(now), closure, closure->cb);
   }
 
   if (!g_shared_mutables.initialized) {
@@ -262,13 +261,13 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
 
   grpc_time_averaged_stats_add_sample(&shard->stats,
                                       ts_to_dbl(gpr_time_sub(deadline, now)));
-  if (timer->deadline < shard->queue_deadline_cap) {
+  if (deadline_atm < shard->queue_deadline_cap) {
     is_first_timer = grpc_timer_heap_add(&shard->heap, timer);
   } else {
     timer->heap_index = INVALID_HEAP_INDEX;
     list_join(&shard->list, timer);
   }
-  if (grpc_timer_trace) {
+  if (GRPC_TRACER_ON(grpc_timer_trace)) {
     gpr_log(GPR_DEBUG, "  .. add to shard %d with queue_deadline_cap=%" PRIdPTR
                        " => is_first_timer=%s",
             (int)(shard - g_shards), shard->queue_deadline_cap,
@@ -289,16 +288,16 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
      grpc_timer_check. */
   if (is_first_timer) {
     gpr_mu_lock(&g_shared_mutables.mu);
-    if (grpc_timer_trace) {
+    if (GRPC_TRACER_ON(grpc_timer_trace)) {
       gpr_log(GPR_DEBUG, "  .. old shard min_deadline=%" PRIdPTR,
               shard->min_deadline);
     }
-    if (timer->deadline < shard->min_deadline) {
+    if (deadline_atm < shard->min_deadline) {
       gpr_atm old_min_deadline = g_shard_queue[0]->min_deadline;
-      shard->min_deadline = timer->deadline;
+      shard->min_deadline = deadline_atm;
       note_deadline_change(shard);
-      if (shard->shard_queue_index == 0 && timer->deadline < old_min_deadline) {
-        gpr_atm_no_barrier_store(&g_shared_mutables.min_timer, timer->deadline);
+      if (shard->shard_queue_index == 0 && deadline_atm < old_min_deadline) {
+        gpr_atm_no_barrier_store(&g_shared_mutables.min_timer, deadline_atm);
         grpc_kick_poller();
       }
     }
@@ -319,7 +318,7 @@ void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer) {
 
   shard_type *shard = &g_shards[GPR_HASH_POINTER(timer, NUM_SHARDS)];
   gpr_mu_lock(&shard->mu);
-  if (grpc_timer_trace) {
+  if (GRPC_TRACER_ON(grpc_timer_trace)) {
     gpr_log(GPR_DEBUG, "TIMER %p: CANCEL pending=%s", timer,
             timer->pending ? "true" : "false");
   }
@@ -355,7 +354,7 @@ static int refill_queue(shard_type *shard, gpr_atm now) {
       saturating_add(GPR_MAX(now, shard->queue_deadline_cap),
                      (gpr_atm)(deadline_delta * 1000.0));
 
-  if (grpc_timer_check_trace) {
+  if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
     gpr_log(GPR_DEBUG, "  .. shard[%d]->queue_deadline_cap --> %" PRIdPTR,
             (int)(shard - g_shards), shard->queue_deadline_cap);
   }
@@ -363,7 +362,7 @@ static int refill_queue(shard_type *shard, gpr_atm now) {
     next = timer->next;
 
     if (timer->deadline < shard->queue_deadline_cap) {
-      if (grpc_timer_check_trace) {
+      if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
         gpr_log(GPR_DEBUG, "  .. add timer with deadline %" PRIdPTR " to heap",
                 timer->deadline);
       }
@@ -380,7 +379,7 @@ static int refill_queue(shard_type *shard, gpr_atm now) {
 static grpc_timer *pop_one(shard_type *shard, gpr_atm now) {
   grpc_timer *timer;
   for (;;) {
-    if (grpc_timer_check_trace) {
+    if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
       gpr_log(GPR_DEBUG, "  .. shard[%d]: heap_empty=%s",
               (int)(shard - g_shards),
               grpc_timer_heap_is_empty(&shard->heap) ? "true" : "false");
@@ -390,13 +389,13 @@ static grpc_timer *pop_one(shard_type *shard, gpr_atm now) {
       if (!refill_queue(shard, now)) return NULL;
     }
     timer = grpc_timer_heap_top(&shard->heap);
-    if (grpc_timer_check_trace) {
+    if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
       gpr_log(GPR_DEBUG,
               "  .. check top timer deadline=%" PRIdPTR " now=%" PRIdPTR,
               timer->deadline, now);
     }
     if (timer->deadline > now) return NULL;
-    if (grpc_timer_trace) {
+    if (GRPC_TRACER_ON(grpc_timer_trace)) {
       gpr_log(GPR_DEBUG, "TIMER %p: FIRE %" PRIdPTR "ms late", timer,
               now - timer->deadline);
     }
@@ -436,7 +435,7 @@ static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_atm now,
   if (gpr_spinlock_trylock(&g_shared_mutables.checker_mu)) {
     gpr_mu_lock(&g_shared_mutables.mu);
 
-    if (grpc_timer_check_trace) {
+    if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
       gpr_log(GPR_DEBUG, "  .. shard[%d]->min_deadline = %" PRIdPTR,
               (int)(g_shard_queue[0] - g_shards),
               g_shard_queue[0]->min_deadline);
@@ -452,7 +451,7 @@ static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_atm now,
       n +=
           pop_timers(exec_ctx, g_shard_queue[0], now, &new_min_deadline, error);
 
-      if (grpc_timer_check_trace) {
+      if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
         gpr_log(GPR_DEBUG, "  .. popped --> %" PRIdPTR
                            ", shard[%d]->min_deadline %" PRIdPTR
                            " --> %" PRIdPTR ", now=%" PRIdPTR,
@@ -509,7 +508,7 @@ bool grpc_timer_check(grpc_exec_ctx *exec_ctx, gpr_timespec now,
       *next =
           atm_to_timespec(GPR_MIN(timespec_to_atm_round_up(*next), min_timer));
     }
-    if (grpc_timer_check_trace) {
+    if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
       gpr_log(GPR_DEBUG,
               "TIMER CHECK SKIP: now_atm=%" PRIdPTR " min_timer=%" PRIdPTR,
               now_atm, min_timer);
@@ -523,7 +522,7 @@ bool grpc_timer_check(grpc_exec_ctx *exec_ctx, gpr_timespec now,
           : GRPC_ERROR_CREATE_FROM_STATIC_STRING("Shutting down timer system");
 
   // tracing
-  if (grpc_timer_check_trace) {
+  if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
     char *next_str;
     if (next == NULL) {
       next_str = gpr_strdup("NULL");
@@ -549,7 +548,7 @@ bool grpc_timer_check(grpc_exec_ctx *exec_ctx, gpr_timespec now,
     *next = atm_to_timespec(next_atm);
   }
   // tracing
-  if (grpc_timer_check_trace) {
+  if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
     char *next_str;
     if (next == NULL) {
       next_str = gpr_strdup("NULL");
diff --git a/src/core/lib/iomgr/timer_manager.c b/src/core/lib/iomgr/timer_manager.c
new file mode 100644
index 0000000000..24085093e7
--- /dev/null
+++ b/src/core/lib/iomgr/timer_manager.c
@@ -0,0 +1,276 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/timer_manager.h"
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/thd.h>
+
+#include "src/core/lib/debug/trace.h"
+#include "src/core/lib/iomgr/timer.h"
+
+typedef struct completed_thread {
+  gpr_thd_id t;
+  struct completed_thread *next;
+} completed_thread;
+
+extern grpc_tracer_flag grpc_timer_check_trace;
+
+// global mutex
+static gpr_mu g_mu;
+// are we multi-threaded
+static bool g_threaded;
+// cv to wait until a thread is needed
+static gpr_cv g_cv_wait;
+// cv for notification when threading ends
+static gpr_cv g_cv_shutdown;
+// number of threads in the system
+static int g_thread_count;
+// number of threads sitting around waiting
+static int g_waiter_count;
+// linked list of threads that have completed (and need joining)
+static completed_thread *g_completed_threads;
+// was the manager kicked by the timer system
+static bool g_kicked;
+// is there a thread waiting until the next timer should fire?
+static bool g_has_timed_waiter;
+// generation counter to track which thread is waiting for the next timer
+static uint64_t g_timed_waiter_generation;
+
+static void timer_thread(void *unused);
+
+static void gc_completed_threads(void) {
+  if (g_completed_threads != NULL) {
+    completed_thread *to_gc = g_completed_threads;
+    g_completed_threads = NULL;
+    gpr_mu_unlock(&g_mu);
+    while (to_gc != NULL) {
+      gpr_thd_join(to_gc->t);
+      completed_thread *next = to_gc->next;
+      gpr_free(to_gc);
+      to_gc = next;
+    }
+    gpr_mu_lock(&g_mu);
+  }
+}
+
+static void start_timer_thread_and_unlock(void) {
+  GPR_ASSERT(g_threaded);
+  ++g_waiter_count;
+  ++g_thread_count;
+  gpr_mu_unlock(&g_mu);
+  if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+    gpr_log(GPR_DEBUG, "Spawn timer thread");
+  }
+  gpr_thd_id thd;
+  gpr_thd_options opt = gpr_thd_options_default();
+  gpr_thd_options_set_joinable(&opt);
+  gpr_thd_new(&thd, timer_thread, NULL, &opt);
+}
+
+void grpc_timer_manager_tick() {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  gpr_timespec next = gpr_inf_future(GPR_CLOCK_MONOTONIC);
+  gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
+  grpc_timer_check(&exec_ctx, now, &next);
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+static void timer_thread(void *unused) {
+  // this threads exec_ctx: we try to run things through to completion here
+  // since it's easy to spin up new threads
+  grpc_exec_ctx exec_ctx =
+      GRPC_EXEC_CTX_INITIALIZER(0, grpc_never_ready_to_finish, NULL);
+  const gpr_timespec inf_future = gpr_inf_future(GPR_CLOCK_MONOTONIC);
+  for (;;) {
+    gpr_timespec next = inf_future;
+    gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
+    // check timer state, updates next to the next time to run a check
+    if (grpc_timer_check(&exec_ctx, now, &next)) {
+      // if there's something to execute...
+      gpr_mu_lock(&g_mu);
+      // remove a waiter from the pool, and start another thread if necessary
+      --g_waiter_count;
+      if (g_waiter_count == 0 && g_threaded) {
+        start_timer_thread_and_unlock();
+      } else {
+        // if there's no thread waiting with a timeout, kick an existing waiter
+        // so that the next deadline is not missed
+        if (!g_has_timed_waiter) {
+          if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+            gpr_log(GPR_DEBUG, "kick untimed waiter");
+          }
+          gpr_cv_signal(&g_cv_wait);
+        }
+        gpr_mu_unlock(&g_mu);
+      }
+      // without our lock, flush the exec_ctx
+      grpc_exec_ctx_flush(&exec_ctx);
+      gpr_mu_lock(&g_mu);
+      // garbage collect any threads hanging out that are dead
+      gc_completed_threads();
+      // get ready to wait again
+      ++g_waiter_count;
+      gpr_mu_unlock(&g_mu);
+    } else {
+      gpr_mu_lock(&g_mu);
+      // if we're not threaded anymore, leave
+      if (!g_threaded) break;
+      // if there's no timed waiter, we should become one: that waiter waits
+      // only until the next timer should expire
+      // all other timers wait forever
+      uint64_t my_timed_waiter_generation = g_timed_waiter_generation - 1;
+      if (!g_has_timed_waiter) {
+        g_has_timed_waiter = true;
+        // we use a generation counter to track the timed waiter so we can
+        // cancel an existing one quickly (and when it actually times out it'll
+        // figure stuff out instead of incurring a wakeup)
+        my_timed_waiter_generation = ++g_timed_waiter_generation;
+        if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+          gpr_log(GPR_DEBUG, "sleep for a while");
+        }
+      } else {
+        next = inf_future;
+        if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+          gpr_log(GPR_DEBUG, "sleep until kicked");
+        }
+      }
+      gpr_cv_wait(&g_cv_wait, &g_mu, next);
+      if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+        gpr_log(GPR_DEBUG, "wait ended: was_timed:%d kicked:%d",
+                my_timed_waiter_generation == g_timed_waiter_generation,
+                g_kicked);
+      }
+      // if this was the timed waiter, then we need to check timers, and flag
+      // that there's now no timed waiter... we'll look for a replacement if
+      // there's work to do after checking timers (code above)
+      if (my_timed_waiter_generation == g_timed_waiter_generation) {
+        g_has_timed_waiter = false;
+      }
+      // if this was a kick from the timer system, consume it (and don't stop
+      // this thread yet)
+      if (g_kicked) {
+        grpc_timer_consume_kick();
+        g_kicked = false;
+      }
+      gpr_mu_unlock(&g_mu);
+    }
+  }
+  // terminate the thread: drop the waiter count, thread count, and let whomever
+  // stopped the threading stuff know that we're done
+  --g_waiter_count;
+  --g_thread_count;
+  if (0 == g_thread_count) {
+    gpr_cv_signal(&g_cv_shutdown);
+  }
+  completed_thread *ct = gpr_malloc(sizeof(*ct));
+  ct->t = gpr_thd_currentid();
+  ct->next = g_completed_threads;
+  g_completed_threads = ct;
+  gpr_mu_unlock(&g_mu);
+  grpc_exec_ctx_finish(&exec_ctx);
+  if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+    gpr_log(GPR_DEBUG, "End timer thread");
+  }
+}
+
+static void start_threads(void) {
+  gpr_mu_lock(&g_mu);
+  if (!g_threaded) {
+    g_threaded = true;
+    start_timer_thread_and_unlock();
+  } else {
+    g_threaded = false;
+    gpr_mu_unlock(&g_mu);
+  }
+}
+
+void grpc_timer_manager_init(void) {
+  gpr_mu_init(&g_mu);
+  gpr_cv_init(&g_cv_wait);
+  gpr_cv_init(&g_cv_shutdown);
+  g_threaded = false;
+  g_thread_count = 0;
+  g_waiter_count = 0;
+  g_completed_threads = NULL;
+
+  start_threads();
+}
+
+static void stop_threads(void) {
+  gpr_mu_lock(&g_mu);
+  if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+    gpr_log(GPR_DEBUG, "stop timer threads: threaded=%d", g_threaded);
+  }
+  if (g_threaded) {
+    g_threaded = false;
+    gpr_cv_broadcast(&g_cv_wait);
+    if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+      gpr_log(GPR_DEBUG, "num timer threads: %d", g_thread_count);
+    }
+    while (g_thread_count > 0) {
+      gpr_cv_wait(&g_cv_shutdown, &g_mu, gpr_inf_future(GPR_CLOCK_REALTIME));
+      if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
+        gpr_log(GPR_DEBUG, "num timer threads: %d", g_thread_count);
+      }
+      gc_completed_threads();
+    }
+  }
+  gpr_mu_unlock(&g_mu);
+}
+
+void grpc_timer_manager_shutdown(void) {
+  stop_threads();
+
+  gpr_mu_destroy(&g_mu);
+  gpr_cv_destroy(&g_cv_wait);
+  gpr_cv_destroy(&g_cv_shutdown);
+}
+
+void grpc_timer_manager_set_threading(bool threaded) {
+  if (threaded) {
+    start_threads();
+  } else {
+    stop_threads();
+  }
+}
+
+void grpc_kick_poller(void) {
+  gpr_mu_lock(&g_mu);
+  g_kicked = true;
+  g_has_timed_waiter = false;
+  ++g_timed_waiter_generation;
+  gpr_cv_signal(&g_cv_wait);
+  gpr_mu_unlock(&g_mu);
+}
diff --git a/src/core/lib/iomgr/timer_manager.h b/src/core/lib/iomgr/timer_manager.h
new file mode 100644
index 0000000000..46729ccea6
--- /dev/null
+++ b/src/core/lib/iomgr/timer_manager.h
@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_TIMER_MANAGER_H
+#define GRPC_CORE_LIB_IOMGR_TIMER_MANAGER_H
+
+#include <stdbool.h>
+
+/* Timer Manager tries to keep one thread waiting for the next timeout at all
+   times */
+
+void grpc_timer_manager_init(void);
+void grpc_timer_manager_shutdown(void);
+
+/* enable/disable threading - must be called after grpc_timer_manager_init and
+ * before grpc_timer_manager_shutdown */
+void grpc_timer_manager_set_threading(bool enabled);
+/* explicitly perform one tick of the timer system - for when threading is
+ * disabled */
+void grpc_timer_manager_tick(void);
+
+#endif /* GRPC_CORE_LIB_IOMGR_TIMER_MANAGER_H */
diff --git a/src/core/lib/iomgr/timer_uv.c b/src/core/lib/iomgr/timer_uv.c
index 8e8a07578c..2952e44b58 100644
--- a/src/core/lib/iomgr/timer_uv.c
+++ b/src/core/lib/iomgr/timer_uv.c
@@ -38,10 +38,14 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/timer.h"
 
 #include <uv.h>
 
+grpc_tracer_flag grpc_timer_trace = GRPC_TRACER_INITIALIZER(false);
+grpc_tracer_flag grpc_timer_check_trace = GRPC_TRACER_INITIALIZER(false);
+
 static void timer_close_callback(uv_handle_t *handle) { gpr_free(handle); }
 
 static void stop_uv_timer(uv_timer_t *handle) {
@@ -100,4 +104,6 @@ bool grpc_timer_check(grpc_exec_ctx *exec_ctx, gpr_timespec now,
 void grpc_timer_list_init(gpr_timespec now) {}
 void grpc_timer_list_shutdown(grpc_exec_ctx *exec_ctx) {}
 
+void grpc_timer_consume_kick(void) {}
+
 #endif /* GRPC_UV */
diff --git a/src/core/lib/security/credentials/google_default/google_default_credentials.c b/src/core/lib/security/credentials/google_default/google_default_credentials.c
index 97501e6788..4d8c451ea8 100644
--- a/src/core/lib/security/credentials/google_default/google_default_credentials.c
+++ b/src/core/lib/security/credentials/google_default/google_default_credentials.c
@@ -99,7 +99,7 @@ static void on_compute_engine_detection_http_response(grpc_exec_ctx *exec_ctx,
 }
 
 static void destroy_pollset(grpc_exec_ctx *exec_ctx, void *p, grpc_error *e) {
-  grpc_pollset_destroy(p);
+  grpc_pollset_destroy(exec_ctx, p);
 }
 
 static int is_stack_running_on_compute_engine(grpc_exec_ctx *exec_ctx) {
diff --git a/src/core/lib/security/credentials/jwt/jwt_credentials.c b/src/core/lib/security/credentials/jwt/jwt_credentials.c
index 178ce89aa6..0e7c1afb02 100644
--- a/src/core/lib/security/credentials/jwt/jwt_credentials.c
+++ b/src/core/lib/security/credentials/jwt/jwt_credentials.c
@@ -171,7 +171,7 @@ static char *redact_private_key(const char *json_key) {
 
 grpc_call_credentials *grpc_service_account_jwt_access_credentials_create(
     const char *json_key, gpr_timespec token_lifetime, void *reserved) {
-  if (grpc_api_trace) {
+  if (GRPC_TRACER_ON(grpc_api_trace)) {
     char *clean_json = redact_private_key(json_key);
     gpr_log(GPR_INFO,
             "grpc_service_account_jwt_access_credentials_create("
diff --git a/src/core/lib/security/credentials/oauth2/oauth2_credentials.c b/src/core/lib/security/credentials/oauth2/oauth2_credentials.c
index ccfb3566c1..29235b6eb3 100644
--- a/src/core/lib/security/credentials/oauth2/oauth2_credentials.c
+++ b/src/core/lib/security/credentials/oauth2/oauth2_credentials.c
@@ -412,7 +412,7 @@ grpc_call_credentials *grpc_google_refresh_token_credentials_create(
     const char *json_refresh_token, void *reserved) {
   grpc_auth_refresh_token token =
       grpc_auth_refresh_token_create_from_string(json_refresh_token);
-  if (grpc_api_trace) {
+  if (GRPC_TRACER_ON(grpc_api_trace)) {
     char *loggable_token = create_loggable_refresh_token(&token);
     gpr_log(GPR_INFO,
             "grpc_refresh_token_credentials_create(json_refresh_token=%s, "
diff --git a/src/core/lib/security/transport/client_auth_filter.c b/src/core/lib/security/transport/client_auth_filter.c
index 1f0daf7325..dff05633ec 100644
--- a/src/core/lib/security/transport/client_auth_filter.c
+++ b/src/core/lib/security/transport/client_auth_filter.c
@@ -253,7 +253,7 @@ static void auth_start_transport_op(grpc_exec_ctx *exec_ctx,
   grpc_linked_mdelem *l;
   grpc_client_security_context *sec_ctx = NULL;
 
-  if (calld->security_context_set == 0 && !op->cancel_stream) {
+  if (!op->cancel_stream && calld->security_context_set == 0) {
     calld->security_context_set = 1;
     GPR_ASSERT(op->payload->context != NULL);
     if (op->payload->context[GRPC_CONTEXT_SECURITY].value == NULL) {
diff --git a/src/core/lib/security/transport/secure_endpoint.c b/src/core/lib/security/transport/secure_endpoint.c
index 0d5c7432c6..48d368a2a7 100644
--- a/src/core/lib/security/transport/secure_endpoint.c
+++ b/src/core/lib/security/transport/secure_endpoint.c
@@ -75,7 +75,7 @@ typedef struct {
   gpr_refcount ref;
 } secure_endpoint;
 
-int grpc_trace_secure_endpoint = 0;
+grpc_tracer_flag grpc_trace_secure_endpoint = GRPC_TRACER_INITIALIZER(false);
 
 static void destroy(grpc_exec_ctx *exec_ctx, secure_endpoint *secure_ep) {
   secure_endpoint *ep = secure_ep;
@@ -137,7 +137,7 @@ static void flush_read_staging_buffer(secure_endpoint *ep, uint8_t **cur,
 
 static void call_read_cb(grpc_exec_ctx *exec_ctx, secure_endpoint *ep,
                          grpc_error *error) {
-  if (grpc_trace_secure_endpoint) {
+  if (GRPC_TRACER_ON(grpc_trace_secure_endpoint)) {
     size_t i;
     for (i = 0; i < ep->read_buffer->count; i++) {
       char *data = grpc_dump_slice(ep->read_buffer->slices[i],
@@ -269,7 +269,7 @@ static void endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *secure_ep,
 
   grpc_slice_buffer_reset_and_unref_internal(exec_ctx, &ep->output_buffer);
 
-  if (grpc_trace_secure_endpoint) {
+  if (GRPC_TRACER_ON(grpc_trace_secure_endpoint)) {
     for (i = 0; i < slices->count; i++) {
       char *data =
           grpc_dump_slice(slices->slices[i], GPR_DUMP_HEX | GPR_DUMP_ASCII);
diff --git a/src/core/lib/security/transport/secure_endpoint.h b/src/core/lib/security/transport/secure_endpoint.h
index a61f40a4fa..f1a5c8cb6d 100644
--- a/src/core/lib/security/transport/secure_endpoint.h
+++ b/src/core/lib/security/transport/secure_endpoint.h
@@ -39,7 +39,7 @@
 
 struct tsi_frame_protector;
 
-extern int grpc_trace_secure_endpoint;
+extern grpc_tracer_flag grpc_trace_secure_endpoint;
 
 /* Takes ownership of protector and to_wrap, and refs leftover_slices. */
 grpc_endpoint *grpc_secure_endpoint_create(
diff --git a/src/core/lib/support/cpu_linux.c b/src/core/lib/support/cpu_linux.c
index 1e50f59823..b826dde160 100644
--- a/src/core/lib/support/cpu_linux.c
+++ b/src/core/lib/support/cpu_linux.c
@@ -67,16 +67,16 @@ unsigned gpr_cpu_num_cores(void) {
 }
 
 unsigned gpr_cpu_current_cpu(void) {
-#ifdef __GLIBC__
+#ifdef GPR_MUSL_LIBC_COMPAT
+  // sched_getcpu() is undefined on musl
+  return 0;
+#else
   int cpu = sched_getcpu();
   if (cpu < 0) {
     gpr_log(GPR_ERROR, "Error determining current CPU: %s\n", strerror(errno));
     return 0;
   }
   return (unsigned)cpu;
-#else
-  // sched_getcpu() is undefined on musl
-  return 0;
 #endif
 }
 
diff --git a/src/core/lib/support/mpscq.c b/src/core/lib/support/mpscq.c
index 6a16e43e2a..822abd075d 100644
--- a/src/core/lib/support/mpscq.c
+++ b/src/core/lib/support/mpscq.c
@@ -55,21 +55,31 @@ bool gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n) {
 }
 
 gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q) {
+  bool empty;
+  return gpr_mpscq_pop_and_check_end(q, &empty);
+}
+
+gpr_mpscq_node *gpr_mpscq_pop_and_check_end(gpr_mpscq *q, bool *empty) {
   gpr_mpscq_node *tail = q->tail;
   gpr_mpscq_node *next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
   if (tail == &q->stub) {
     // indicates the list is actually (ephemerally) empty
-    if (next == NULL) return NULL;
+    if (next == NULL) {
+      *empty = true;
+      return NULL;
+    }
     q->tail = next;
     tail = next;
     next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
   }
   if (next != NULL) {
+    *empty = false;
     q->tail = next;
     return tail;
   }
   gpr_mpscq_node *head = (gpr_mpscq_node *)gpr_atm_acq_load(&q->head);
   if (tail != head) {
+    *empty = false;
     // indicates a retry is in order: we're still adding
     return NULL;
   }
@@ -80,6 +90,7 @@ gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q) {
     return tail;
   }
   // indicates a retry is in order: we're still adding
+  *empty = false;
   return NULL;
 }
 
diff --git a/src/core/lib/support/mpscq.h b/src/core/lib/support/mpscq.h
index cb6456f2c8..b3a171678a 100644
--- a/src/core/lib/support/mpscq.h
+++ b/src/core/lib/support/mpscq.h
@@ -67,6 +67,8 @@ bool gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n);
 // the queue is empty!!)
 // Thread compatible - can only be called from one thread at a time
 gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q);
+// Pop a node; sets *empty to true if the queue is empty, or false if it is not
+gpr_mpscq_node *gpr_mpscq_pop_and_check_end(gpr_mpscq *q, bool *empty);
 
 // An mpscq with a spinlock: it's safe to pop from multiple threads, but doing
 // only one thread will succeed concurrently
diff --git a/src/core/lib/support/wrap_memcpy.c b/src/core/lib/support/wrap_memcpy.c
index 050cc6db5e..deb8d6b198 100644
--- a/src/core/lib/support/wrap_memcpy.c
+++ b/src/core/lib/support/wrap_memcpy.c
@@ -31,6 +31,8 @@
  *
  */
 
+#include <grpc/support/port_platform.h>
+
 #include <string.h>
 
 /* Provide a wrapped memcpy for targets that need to be backwards
@@ -40,7 +42,7 @@
  */
 
 #ifdef __linux__
-#if defined(__x86_64__) && defined(__GNU_LIBRARY__)
+#if defined(__x86_64__) && !defined(GPR_MUSL_LIBC_COMPAT)
 __asm__(".symver memcpy,memcpy@GLIBC_2.2.5");
 void *__wrap_memcpy(void *destination, const void *source, size_t num) {
   return memcpy(destination, source, num);
diff --git a/src/core/lib/surface/alarm.c b/src/core/lib/surface/alarm.c
index e71c0ebfc5..b72d534b7e 100644
--- a/src/core/lib/surface/alarm.c
+++ b/src/core/lib/surface/alarm.c
@@ -81,7 +81,9 @@ void grpc_alarm_cancel(grpc_alarm *alarm) {
 }
 
 void grpc_alarm_destroy(grpc_alarm *alarm) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_alarm_cancel(alarm);
-  GRPC_CQ_INTERNAL_UNREF(alarm->cq, "alarm");
+  GRPC_CQ_INTERNAL_UNREF(&exec_ctx, alarm->cq, "alarm");
   gpr_free(alarm);
+  grpc_exec_ctx_finish(&exec_ctx);
 }
diff --git a/src/core/lib/surface/api_trace.c b/src/core/lib/surface/api_trace.c
index 79e3e5ca9b..d8941cdf42 100644
--- a/src/core/lib/surface/api_trace.c
+++ b/src/core/lib/surface/api_trace.c
@@ -32,5 +32,6 @@
  */
 
 #include "src/core/lib/surface/api_trace.h"
+#include "src/core/lib/debug/trace.h"
 
-int grpc_api_trace = 0;
+grpc_tracer_flag grpc_api_trace = GRPC_TRACER_INITIALIZER(false);
diff --git a/src/core/lib/surface/api_trace.h b/src/core/lib/surface/api_trace.h
index c60aaba5e9..d4fbc8d90d 100644
--- a/src/core/lib/surface/api_trace.h
+++ b/src/core/lib/surface/api_trace.h
@@ -37,7 +37,7 @@
 #include <grpc/support/log.h>
 #include "src/core/lib/debug/trace.h"
 
-extern int grpc_api_trace;
+extern grpc_tracer_flag grpc_api_trace;
 
 /* Provide unwrapping macros because we're in C89 and variadic macros weren't
    introduced until C99... */
@@ -58,7 +58,7 @@ extern int grpc_api_trace;
 /* Due to the limitations of C89's preprocessor, the arity of the var-arg list
    'nargs' must be specified. */
 #define GRPC_API_TRACE(fmt, nargs, args)                      \
-  if (grpc_api_trace) {                                       \
+  if (GRPC_TRACER_ON(grpc_api_trace)) {                       \
     gpr_log(GPR_INFO, fmt GRPC_API_TRACE_UNWRAP##nargs args); \
   }
 
diff --git a/src/core/lib/surface/call.c b/src/core/lib/surface/call.c
index 7525806583..201969cd45 100644
--- a/src/core/lib/surface/call.c
+++ b/src/core/lib/surface/call.c
@@ -244,8 +244,8 @@ struct grpc_call {
   void *saved_receiving_stream_ready_bctlp;
 };
 
-int grpc_call_error_trace = 0;
-int grpc_compression_trace = 0;
+grpc_tracer_flag grpc_call_error_trace = GRPC_TRACER_INITIALIZER(false);
+grpc_tracer_flag grpc_compression_trace = GRPC_TRACER_INITIALIZER(false);
 
 #define CALL_STACK_FROM_CALL(call) ((grpc_call_stack *)((call) + 1))
 #define CALL_FROM_CALL_STACK(call_stack) (((grpc_call *)(call_stack)) - 1)
@@ -521,7 +521,7 @@ static void destroy_call(grpc_exec_ctx *exec_ctx, void *call,
     }
   }
   if (c->cq) {
-    GRPC_CQ_INTERNAL_UNREF(c->cq, "bind");
+    GRPC_CQ_INTERNAL_UNREF(exec_ctx, c->cq, "bind");
   }
 
   get_final_status(call, set_status_value_directly, &c->final_info.final_status,
@@ -702,7 +702,7 @@ static void get_final_status(grpc_call *call,
   for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
     status[i] = unpack_received_status(gpr_atm_acq_load(&call->status[i]));
   }
-  if (grpc_call_error_trace) {
+  if (GRPC_TRACER_ON(grpc_call_error_trace)) {
     gpr_log(GPR_DEBUG, "get_final_status %s", call->is_client ? "CLI" : "SVR");
     for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
       if (status[i].is_set) {
@@ -1259,7 +1259,7 @@ static void receiving_slice_ready(grpc_exec_ctx *exec_ctx, void *bctlp,
   }
 
   if (error != GRPC_ERROR_NONE) {
-    if (grpc_trace_operation_failures) {
+    if (GRPC_TRACER_ON(grpc_trace_operation_failures)) {
       GRPC_LOG_IF_ERROR("receiving_slice_ready", GRPC_ERROR_REF(error));
     }
     grpc_byte_stream_destroy(exec_ctx, call->receiving_stream);
@@ -1355,8 +1355,7 @@ static void validate_filtered_metadata(grpc_exec_ctx *exec_ctx,
   GPR_ASSERT(call->encodings_accepted_by_peer != 0);
   if (!GPR_BITGET(call->encodings_accepted_by_peer,
                   call->incoming_compression_algorithm)) {
-    extern int grpc_compression_trace;
-    if (grpc_compression_trace) {
+    if (GRPC_TRACER_ON(grpc_compression_trace)) {
       char *algo_name = NULL;
       grpc_compression_algorithm_name(call->incoming_compression_algorithm,
                                       &algo_name);
diff --git a/src/core/lib/surface/call.h b/src/core/lib/surface/call.h
index 7d4d0db28d..256a5fa2fe 100644
--- a/src/core/lib/surface/call.h
+++ b/src/core/lib/surface/call.h
@@ -117,7 +117,8 @@ void grpc_call_context_set(grpc_call *call, grpc_context_index elem,
 void *grpc_call_context_get(grpc_call *call, grpc_context_index elem);
 
 #define GRPC_CALL_LOG_BATCH(sev, call, ops, nops, tag) \
-  if (grpc_api_trace) grpc_call_log_batch(sev, call, ops, nops, tag)
+  if (GRPC_TRACER_ON(grpc_api_trace))                  \
+  grpc_call_log_batch(sev, call, ops, nops, tag)
 
 uint8_t grpc_call_is_client(grpc_call *call);
 
@@ -126,7 +127,8 @@ uint8_t grpc_call_is_client(grpc_call *call);
 grpc_compression_algorithm grpc_call_compression_for_level(
     grpc_call *call, grpc_compression_level level);
 
-extern int grpc_call_error_trace;
+extern grpc_tracer_flag grpc_call_error_trace;
+extern grpc_tracer_flag grpc_compression_trace;
 
 #ifdef __cplusplus
 }
diff --git a/src/core/lib/surface/completion_queue.c b/src/core/lib/surface/completion_queue.c
index eae3f103b1..df5b70205c 100644
--- a/src/core/lib/surface/completion_queue.c
+++ b/src/core/lib/surface/completion_queue.c
@@ -50,9 +50,9 @@
 #include "src/core/lib/surface/call.h"
 #include "src/core/lib/surface/event_string.h"
 
-int grpc_trace_operation_failures;
+grpc_tracer_flag grpc_trace_operation_failures = GRPC_TRACER_INITIALIZER(false);
 #ifndef NDEBUG
-int grpc_trace_pending_tags;
+grpc_tracer_flag grpc_trace_pending_tags = GRPC_TRACER_INITIALIZER(false);
 #endif
 
 typedef struct {
@@ -72,7 +72,7 @@ typedef struct {
                       gpr_timespec deadline);
   void (*shutdown)(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                    grpc_closure *closure);
-  void (*destroy)(grpc_pollset *pollset);
+  void (*destroy)(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset);
 } cq_poller_vtable;
 
 typedef struct non_polling_worker {
@@ -98,7 +98,8 @@ static void non_polling_poller_init(grpc_pollset *pollset, gpr_mu **mu) {
   *mu = &npp->mu;
 }
 
-static void non_polling_poller_destroy(grpc_pollset *pollset) {
+static void non_polling_poller_destroy(grpc_exec_ctx *exec_ctx,
+                                       grpc_pollset *pollset) {
   non_polling_poller *npp = (non_polling_poller *)pollset;
   gpr_mu_destroy(&npp->mu);
 }
@@ -242,15 +243,16 @@ struct grpc_completion_queue {
 #define POLLSET_FROM_CQ(cq) ((grpc_pollset *)(cq + 1))
 #define CQ_FROM_POLLSET(ps) (((grpc_completion_queue *)ps) - 1)
 
-int grpc_cq_pluck_trace;
-int grpc_cq_event_timeout_trace;
+grpc_tracer_flag grpc_cq_pluck_trace = GRPC_TRACER_INITIALIZER(true);
+grpc_tracer_flag grpc_cq_event_timeout_trace = GRPC_TRACER_INITIALIZER(true);
 
-#define GRPC_SURFACE_TRACE_RETURNED_EVENT(cq, event)                  \
-  if (grpc_api_trace &&                                               \
-      (grpc_cq_pluck_trace || (event)->type != GRPC_QUEUE_TIMEOUT)) { \
-    char *_ev = grpc_event_string(event);                             \
-    gpr_log(GPR_INFO, "RETURN_EVENT[%p]: %s", cq, _ev);               \
-    gpr_free(_ev);                                                    \
+#define GRPC_SURFACE_TRACE_RETURNED_EVENT(cq, event)    \
+  if (GRPC_TRACER_ON(grpc_api_trace) &&                 \
+      (GRPC_TRACER_ON(grpc_cq_pluck_trace) ||           \
+       (event)->type != GRPC_QUEUE_TIMEOUT)) {          \
+    char *_ev = grpc_event_string(event);               \
+    gpr_log(GPR_INFO, "RETURN_EVENT[%p]: %s", cq, _ev); \
+    gpr_free(_ev);                                      \
   }
 
 static void on_pollset_shutdown_done(grpc_exec_ctx *exec_ctx, void *cc,
@@ -322,20 +324,21 @@ void grpc_cq_internal_ref(grpc_completion_queue *cc) {
 static void on_pollset_shutdown_done(grpc_exec_ctx *exec_ctx, void *arg,
                                      grpc_error *error) {
   grpc_completion_queue *cc = arg;
-  GRPC_CQ_INTERNAL_UNREF(cc, "pollset_destroy");
+  GRPC_CQ_INTERNAL_UNREF(exec_ctx, cc, "pollset_destroy");
 }
 
 #ifdef GRPC_CQ_REF_COUNT_DEBUG
-void grpc_cq_internal_unref(grpc_completion_queue *cc, const char *reason,
-                            const char *file, int line) {
+void grpc_cq_internal_unref(grpc_exec_ctx *exec_ctx, grpc_completion_queue *cc,
+                            const char *reason, const char *file, int line) {
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, "CQ:%p unref %d -> %d %s", cc,
           (int)cc->owning_refs.count, (int)cc->owning_refs.count - 1, reason);
 #else
-void grpc_cq_internal_unref(grpc_completion_queue *cc) {
+void grpc_cq_internal_unref(grpc_exec_ctx *exec_ctx,
+                            grpc_completion_queue *cc) {
 #endif
   if (gpr_unref(&cc->owning_refs)) {
     GPR_ASSERT(cc->completed_head.next == (uintptr_t)&cc->completed_head);
-    cc->poller_vtable->destroy(POLLSET_FROM_CQ(cc));
+    cc->poller_vtable->destroy(exec_ctx, POLLSET_FROM_CQ(cc));
 #ifndef NDEBUG
     gpr_free(cc->outstanding_tags);
 #endif
@@ -375,14 +378,16 @@ void grpc_cq_end_op(grpc_exec_ctx *exec_ctx, grpc_completion_queue *cc,
 #endif
 
   GPR_TIMER_BEGIN("grpc_cq_end_op", 0);
-  if (grpc_api_trace ||
-      (grpc_trace_operation_failures && error != GRPC_ERROR_NONE)) {
+  if (GRPC_TRACER_ON(grpc_api_trace) ||
+      (GRPC_TRACER_ON(grpc_trace_operation_failures) &&
+       error != GRPC_ERROR_NONE)) {
     const char *errmsg = grpc_error_string(error);
     GRPC_API_TRACE(
         "grpc_cq_end_op(exec_ctx=%p, cc=%p, tag=%p, error=%s, done=%p, "
         "done_arg=%p, storage=%p)",
         7, (exec_ctx, cc, tag, errmsg, done, done_arg, storage));
-    if (grpc_trace_operation_failures && error != GRPC_ERROR_NONE) {
+    if (GRPC_TRACER_ON(grpc_trace_operation_failures) &&
+        error != GRPC_ERROR_NONE) {
       gpr_log(GPR_ERROR, "Operation failed: tag=%p, error=%s", tag, errmsg);
     }
   }
@@ -481,7 +486,7 @@ static bool cq_is_next_finished(grpc_exec_ctx *exec_ctx, void *arg) {
 
 #ifndef NDEBUG
 static void dump_pending_tags(grpc_completion_queue *cc) {
-  if (!grpc_trace_pending_tags) return;
+  if (!GRPC_TRACER_ON(grpc_trace_pending_tags)) return;
 
   gpr_strvec v;
   gpr_strvec_init(&v);
@@ -580,36 +585,23 @@ grpc_event grpc_completion_queue_next(grpc_completion_queue *cc,
       dump_pending_tags(cc);
       break;
     }
-    /* Check alarms - these are a global resource so we just ping
-       each time through on every pollset.
-       May update deadline to ensure timely wakeups.
-       TODO(ctiller): can this work be localized? */
-    gpr_timespec iteration_deadline = deadline;
-    if (grpc_timer_check(&exec_ctx, now, &iteration_deadline)) {
-      GPR_TIMER_MARK("alarm_triggered", 0);
+    grpc_error *err = cc->poller_vtable->work(&exec_ctx, POLLSET_FROM_CQ(cc),
+                                              NULL, now, deadline);
+    if (err != GRPC_ERROR_NONE) {
       gpr_mu_unlock(cc->mu);
-      grpc_exec_ctx_flush(&exec_ctx);
-      gpr_mu_lock(cc->mu);
-      continue;
-    } else {
-      grpc_error *err = cc->poller_vtable->work(&exec_ctx, POLLSET_FROM_CQ(cc),
-                                                NULL, now, iteration_deadline);
-      if (err != GRPC_ERROR_NONE) {
-        gpr_mu_unlock(cc->mu);
-        const char *msg = grpc_error_string(err);
-        gpr_log(GPR_ERROR, "Completion queue next failed: %s", msg);
+      const char *msg = grpc_error_string(err);
+      gpr_log(GPR_ERROR, "Completion queue next failed: %s", msg);
 
-        GRPC_ERROR_UNREF(err);
-        memset(&ret, 0, sizeof(ret));
-        ret.type = GRPC_QUEUE_TIMEOUT;
-        dump_pending_tags(cc);
-        break;
-      }
+      GRPC_ERROR_UNREF(err);
+      memset(&ret, 0, sizeof(ret));
+      ret.type = GRPC_QUEUE_TIMEOUT;
+      dump_pending_tags(cc);
+      break;
     }
     is_finished_arg.first_loop = false;
   }
   GRPC_SURFACE_TRACE_RETURNED_EVENT(cc, &ret);
-  GRPC_CQ_INTERNAL_UNREF(cc, "next");
+  GRPC_CQ_INTERNAL_UNREF(&exec_ctx, cc, "next");
   grpc_exec_ctx_finish(&exec_ctx);
   GPR_ASSERT(is_finished_arg.stolen_completion == NULL);
 
@@ -690,7 +682,7 @@ grpc_event grpc_completion_queue_pluck(grpc_completion_queue *cc, void *tag,
     abort();
   }
 
-  if (grpc_cq_pluck_trace) {
+  if (GRPC_TRACER_ON(grpc_cq_pluck_trace)) {
     GRPC_API_TRACE(
         "grpc_completion_queue_pluck("
         "cc=%p, tag=%p, "
@@ -773,38 +765,26 @@ grpc_event grpc_completion_queue_pluck(grpc_completion_queue *cc, void *tag,
       dump_pending_tags(cc);
       break;
     }
-    /* Check alarms - these are a global resource so we just ping
-       each time through on every pollset.
-       May update deadline to ensure timely wakeups.
-       TODO(ctiller): can this work be localized? */
-    gpr_timespec iteration_deadline = deadline;
-    if (grpc_timer_check(&exec_ctx, now, &iteration_deadline)) {
-      GPR_TIMER_MARK("alarm_triggered", 0);
+    grpc_error *err = cc->poller_vtable->work(&exec_ctx, POLLSET_FROM_CQ(cc),
+                                              &worker, now, deadline);
+    if (err != GRPC_ERROR_NONE) {
+      del_plucker(cc, tag, &worker);
       gpr_mu_unlock(cc->mu);
-      grpc_exec_ctx_flush(&exec_ctx);
-      gpr_mu_lock(cc->mu);
-    } else {
-      grpc_error *err = cc->poller_vtable->work(
-          &exec_ctx, POLLSET_FROM_CQ(cc), &worker, now, iteration_deadline);
-      if (err != GRPC_ERROR_NONE) {
-        del_plucker(cc, tag, &worker);
-        gpr_mu_unlock(cc->mu);
-        const char *msg = grpc_error_string(err);
-        gpr_log(GPR_ERROR, "Completion queue next failed: %s", msg);
+      const char *msg = grpc_error_string(err);
+      gpr_log(GPR_ERROR, "Completion queue next failed: %s", msg);
 
-        GRPC_ERROR_UNREF(err);
-        memset(&ret, 0, sizeof(ret));
-        ret.type = GRPC_QUEUE_TIMEOUT;
-        dump_pending_tags(cc);
-        break;
-      }
+      GRPC_ERROR_UNREF(err);
+      memset(&ret, 0, sizeof(ret));
+      ret.type = GRPC_QUEUE_TIMEOUT;
+      dump_pending_tags(cc);
+      break;
     }
     is_finished_arg.first_loop = false;
     del_plucker(cc, tag, &worker);
   }
 done:
   GRPC_SURFACE_TRACE_RETURNED_EVENT(cc, &ret);
-  GRPC_CQ_INTERNAL_UNREF(cc, "pluck");
+  GRPC_CQ_INTERNAL_UNREF(&exec_ctx, cc, "pluck");
   grpc_exec_ctx_finish(&exec_ctx);
   GPR_ASSERT(is_finished_arg.stolen_completion == NULL);
 
@@ -841,7 +821,9 @@ void grpc_completion_queue_destroy(grpc_completion_queue *cc) {
   GRPC_API_TRACE("grpc_completion_queue_destroy(cc=%p)", 1, (cc));
   GPR_TIMER_BEGIN("grpc_completion_queue_destroy", 0);
   grpc_completion_queue_shutdown(cc);
-  GRPC_CQ_INTERNAL_UNREF(cc, "destroy");
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  GRPC_CQ_INTERNAL_UNREF(&exec_ctx, cc, "destroy");
+  grpc_exec_ctx_finish(&exec_ctx);
   GPR_TIMER_END("grpc_completion_queue_destroy", 0);
 }
 
diff --git a/src/core/lib/surface/completion_queue.h b/src/core/lib/surface/completion_queue.h
index a932087939..8d9ce2ec02 100644
--- a/src/core/lib/surface/completion_queue.h
+++ b/src/core/lib/surface/completion_queue.h
@@ -37,15 +37,16 @@
 /* Internal API for completion queues */
 
 #include <grpc/grpc.h>
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/pollset.h"
 
 /* These trace flags default to 1. The corresponding lines are only traced
    if grpc_api_trace is also truthy */
-extern int grpc_cq_pluck_trace;
-extern int grpc_cq_event_timeout_trace;
-extern int grpc_trace_operation_failures;
+extern grpc_tracer_flag grpc_cq_pluck_trace;
+extern grpc_tracer_flag grpc_cq_event_timeout_trace;
+extern grpc_tracer_flag grpc_trace_operation_failures;
 #ifndef NDEBUG
-extern int grpc_trace_pending_tags;
+extern grpc_tracer_flag grpc_trace_pending_tags;
 #endif
 
 typedef struct grpc_cq_completion {
@@ -65,17 +66,17 @@ typedef struct grpc_cq_completion {
 #ifdef GRPC_CQ_REF_COUNT_DEBUG
 void grpc_cq_internal_ref(grpc_completion_queue *cc, const char *reason,
                           const char *file, int line);
-void grpc_cq_internal_unref(grpc_completion_queue *cc, const char *reason,
-                            const char *file, int line);
+void grpc_cq_internal_unref(grpc_exec_ctx *exec_ctx, grpc_completion_queue *cc,
+                            const char *reason, const char *file, int line);
 #define GRPC_CQ_INTERNAL_REF(cc, reason) \
   grpc_cq_internal_ref(cc, reason, __FILE__, __LINE__)
-#define GRPC_CQ_INTERNAL_UNREF(cc, reason) \
-  grpc_cq_internal_unref(cc, reason, __FILE__, __LINE__)
+#define GRPC_CQ_INTERNAL_UNREF(ec, cc, reason) \
+  grpc_cq_internal_unref(ec, cc, reason, __FILE__, __LINE__)
 #else
 void grpc_cq_internal_ref(grpc_completion_queue *cc);
-void grpc_cq_internal_unref(grpc_completion_queue *cc);
+void grpc_cq_internal_unref(grpc_exec_ctx *exec_ctx, grpc_completion_queue *cc);
 #define GRPC_CQ_INTERNAL_REF(cc, reason) grpc_cq_internal_ref(cc)
-#define GRPC_CQ_INTERNAL_UNREF(cc, reason) grpc_cq_internal_unref(cc)
+#define GRPC_CQ_INTERNAL_UNREF(ec, cc, reason) grpc_cq_internal_unref(ec, cc)
 #endif
 
 /* Flag that an operation is beginning: the completion channel will not finish
diff --git a/src/core/lib/surface/init.c b/src/core/lib/surface/init.c
index 4b381b1954..6163776152 100644
--- a/src/core/lib/surface/init.c
+++ b/src/core/lib/surface/init.c
@@ -145,10 +145,8 @@ void grpc_init(void) {
     grpc_register_tracer("server_channel", &grpc_server_channel_trace);
     grpc_register_tracer("bdp_estimator", &grpc_bdp_estimator_trace);
     // Default pluck trace to 1
-    grpc_cq_pluck_trace = 1;
     grpc_register_tracer("queue_timeout", &grpc_cq_event_timeout_trace);
     // Default timeout trace to 1
-    grpc_cq_event_timeout_trace = 1;
     grpc_register_tracer("op_failure", &grpc_trace_operation_failures);
     grpc_register_tracer("resource_quota", &grpc_resource_quota_trace);
     grpc_register_tracer("call_error", &grpc_call_error_trace);
@@ -173,6 +171,7 @@ void grpc_init(void) {
     grpc_tracer_init("GRPC_TRACE");
     /* no more changes to channel init pipelines */
     grpc_channel_init_finalize();
+    grpc_iomgr_start();
   }
   gpr_mu_unlock(&g_init_mu);
   GRPC_API_TRACE("grpc_init(void)", 0, ());
diff --git a/src/core/lib/surface/server.c b/src/core/lib/surface/server.c
index 4ab538132a..7e4ae421a0 100644
--- a/src/core/lib/surface/server.c
+++ b/src/core/lib/surface/server.c
@@ -74,7 +74,7 @@ typedef struct registered_method registered_method;
 
 typedef enum { BATCH_CALL, REGISTERED_CALL } requested_call_type;
 
-int grpc_server_channel_trace = 0;
+grpc_tracer_flag grpc_server_channel_trace = GRPC_TRACER_INITIALIZER(false);
 
 typedef struct requested_call {
   gpr_mpscq_node request_link; /* must be first */
@@ -408,7 +408,7 @@ static void server_delete(grpc_exec_ctx *exec_ctx, grpc_server *server) {
     request_matcher_destroy(&server->unregistered_request_matcher);
   }
   for (i = 0; i < server->cq_count; i++) {
-    GRPC_CQ_INTERNAL_UNREF(server->cqs[i], "server");
+    GRPC_CQ_INTERNAL_UNREF(exec_ctx, server->cqs[i], "server");
   }
   gpr_free(server->cqs);
   gpr_free(server->pollsets);
@@ -450,7 +450,7 @@ static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand,
   grpc_closure_init(&chand->finish_destroy_channel_closure,
                     finish_destroy_channel, chand, grpc_schedule_on_exec_ctx);
 
-  if (grpc_server_channel_trace && error != GRPC_ERROR_NONE) {
+  if (GRPC_TRACER_ON(grpc_server_channel_trace) && error != GRPC_ERROR_NONE) {
     const char *msg = grpc_error_string(error);
     gpr_log(GPR_INFO, "Disconnected client: %s", msg);
   }
diff --git a/src/core/lib/surface/server.h b/src/core/lib/surface/server.h
index a85d9f4964..cd2fca0fe0 100644
--- a/src/core/lib/surface/server.h
+++ b/src/core/lib/surface/server.h
@@ -36,12 +36,13 @@
 
 #include <grpc/grpc.h>
 #include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/transport/transport.h"
 
 extern const grpc_channel_filter grpc_server_top_filter;
 
 /** Lightweight tracing of server channel state */
-extern int grpc_server_channel_trace;
+extern grpc_tracer_flag grpc_server_channel_trace;
 
 /* Add a listener to the server: when the server starts, it will call start,
    and when it shuts down, it will call destroy */
diff --git a/src/core/lib/transport/bdp_estimator.c b/src/core/lib/transport/bdp_estimator.c
index e1483677fd..da8019d98b 100644
--- a/src/core/lib/transport/bdp_estimator.c
+++ b/src/core/lib/transport/bdp_estimator.c
@@ -38,12 +38,13 @@
 #include <grpc/support/log.h>
 #include <grpc/support/useful.h>
 
-int grpc_bdp_estimator_trace = 0;
+grpc_tracer_flag grpc_bdp_estimator_trace = GRPC_TRACER_INITIALIZER(false);
 
 void grpc_bdp_estimator_init(grpc_bdp_estimator *estimator, const char *name) {
   estimator->estimate = 65536;
   estimator->ping_state = GRPC_BDP_PING_UNSCHEDULED;
   estimator->name = name;
+  estimator->bw_est = 0;
 }
 
 bool grpc_bdp_estimator_get_estimate(grpc_bdp_estimator *estimator,
@@ -67,7 +68,7 @@ bool grpc_bdp_estimator_add_incoming_bytes(grpc_bdp_estimator *estimator,
 }
 
 void grpc_bdp_estimator_schedule_ping(grpc_bdp_estimator *estimator) {
-  if (grpc_bdp_estimator_trace) {
+  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
     gpr_log(GPR_DEBUG, "bdp[%s]:sched acc=%" PRId64 " est=%" PRId64,
             estimator->name, estimator->accumulator, estimator->estimate);
   }
@@ -77,24 +78,34 @@ void grpc_bdp_estimator_schedule_ping(grpc_bdp_estimator *estimator) {
 }
 
 void grpc_bdp_estimator_start_ping(grpc_bdp_estimator *estimator) {
-  if (grpc_bdp_estimator_trace) {
+  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
     gpr_log(GPR_DEBUG, "bdp[%s]:start acc=%" PRId64 " est=%" PRId64,
             estimator->name, estimator->accumulator, estimator->estimate);
   }
   GPR_ASSERT(estimator->ping_state == GRPC_BDP_PING_SCHEDULED);
   estimator->ping_state = GRPC_BDP_PING_STARTED;
   estimator->accumulator = 0;
+  estimator->ping_start_time = gpr_now(GPR_CLOCK_MONOTONIC);
 }
 
 void grpc_bdp_estimator_complete_ping(grpc_bdp_estimator *estimator) {
-  if (grpc_bdp_estimator_trace) {
-    gpr_log(GPR_DEBUG, "bdp[%s]:complete acc=%" PRId64 " est=%" PRId64,
-            estimator->name, estimator->accumulator, estimator->estimate);
+  gpr_timespec dt_ts =
+      gpr_time_sub(gpr_now(GPR_CLOCK_MONOTONIC), estimator->ping_start_time);
+  double dt = (double)dt_ts.tv_sec + 1e-9 * (double)dt_ts.tv_nsec;
+  double bw = dt > 0 ? ((double)estimator->accumulator / dt) : 0;
+  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
+    gpr_log(GPR_DEBUG, "bdp[%s]:complete acc=%" PRId64 " est=%" PRId64
+                       " dt=%lf bw=%lfMbs bw_est=%lfMbs",
+            estimator->name, estimator->accumulator, estimator->estimate, dt,
+            bw / 125000.0, estimator->bw_est / 125000.0);
   }
   GPR_ASSERT(estimator->ping_state == GRPC_BDP_PING_STARTED);
-  if (estimator->accumulator > 2 * estimator->estimate / 3) {
-    estimator->estimate *= 2;
-    if (grpc_bdp_estimator_trace) {
+  if (estimator->accumulator > 2 * estimator->estimate / 3 &&
+      bw > estimator->bw_est) {
+    estimator->estimate =
+        GPR_MAX(estimator->accumulator, estimator->estimate * 2);
+    estimator->bw_est = bw;
+    if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
       gpr_log(GPR_DEBUG, "bdp[%s]: estimate increased to %" PRId64,
               estimator->name, estimator->estimate);
     }
diff --git a/src/core/lib/transport/bdp_estimator.h b/src/core/lib/transport/bdp_estimator.h
index df8d1f6fc0..135376edd7 100644
--- a/src/core/lib/transport/bdp_estimator.h
+++ b/src/core/lib/transport/bdp_estimator.h
@@ -34,13 +34,15 @@
 #ifndef GRPC_CORE_LIB_TRANSPORT_BDP_ESTIMATOR_H
 #define GRPC_CORE_LIB_TRANSPORT_BDP_ESTIMATOR_H
 
+#include <grpc/support/time.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include "src/core/lib/debug/trace.h"
 
 #define GRPC_BDP_SAMPLES 16
 #define GRPC_BDP_MIN_SAMPLES_FOR_ESTIMATE 3
 
-extern int grpc_bdp_estimator_trace;
+extern grpc_tracer_flag grpc_bdp_estimator_trace;
 
 typedef enum {
   GRPC_BDP_PING_UNSCHEDULED,
@@ -52,6 +54,8 @@ typedef struct grpc_bdp_estimator {
   grpc_bdp_estimator_ping_state ping_state;
   int64_t accumulator;
   int64_t estimate;
+  gpr_timespec ping_start_time;
+  double bw_est;
   const char *name;
 } grpc_bdp_estimator;
 
diff --git a/src/core/lib/transport/connectivity_state.c b/src/core/lib/transport/connectivity_state.c
index 3757b25267..e30cd523fa 100644
--- a/src/core/lib/transport/connectivity_state.c
+++ b/src/core/lib/transport/connectivity_state.c
@@ -39,7 +39,7 @@
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 
-int grpc_connectivity_state_trace = 0;
+grpc_tracer_flag grpc_connectivity_state_trace = GRPC_TRACER_INITIALIZER(false);
 
 const char *grpc_connectivity_state_name(grpc_connectivity_state state) {
   switch (state) {
@@ -94,7 +94,7 @@ grpc_connectivity_state grpc_connectivity_state_check(
   grpc_connectivity_state cur =
       (grpc_connectivity_state)gpr_atm_no_barrier_load(
           &tracker->current_state_atm);
-  if (grpc_connectivity_state_trace) {
+  if (GRPC_TRACER_ON(grpc_connectivity_state_trace)) {
     gpr_log(GPR_DEBUG, "CONWATCH: %p %s: get %s", tracker, tracker->name,
             grpc_connectivity_state_name(cur));
   }
@@ -106,7 +106,7 @@ grpc_connectivity_state grpc_connectivity_state_get(
   grpc_connectivity_state cur =
       (grpc_connectivity_state)gpr_atm_no_barrier_load(
           &tracker->current_state_atm);
-  if (grpc_connectivity_state_trace) {
+  if (GRPC_TRACER_ON(grpc_connectivity_state_trace)) {
     gpr_log(GPR_DEBUG, "CONWATCH: %p %s: get %s", tracker, tracker->name,
             grpc_connectivity_state_name(cur));
   }
@@ -127,7 +127,7 @@ bool grpc_connectivity_state_notify_on_state_change(
   grpc_connectivity_state cur =
       (grpc_connectivity_state)gpr_atm_no_barrier_load(
           &tracker->current_state_atm);
-  if (grpc_connectivity_state_trace) {
+  if (GRPC_TRACER_ON(grpc_connectivity_state_trace)) {
     if (current == NULL) {
       gpr_log(GPR_DEBUG, "CONWATCH: %p %s: unsubscribe notify=%p", tracker,
               tracker->name, notify);
@@ -180,7 +180,7 @@ void grpc_connectivity_state_set(grpc_exec_ctx *exec_ctx,
       (grpc_connectivity_state)gpr_atm_no_barrier_load(
           &tracker->current_state_atm);
   grpc_connectivity_state_watcher *w;
-  if (grpc_connectivity_state_trace) {
+  if (GRPC_TRACER_ON(grpc_connectivity_state_trace)) {
     const char *error_string = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "SET: %p %s: %s --> %s [%s] error=%p %s", tracker,
             tracker->name, grpc_connectivity_state_name(cur),
@@ -208,7 +208,7 @@ void grpc_connectivity_state_set(grpc_exec_ctx *exec_ctx,
   while ((w = tracker->watchers) != NULL) {
     *w->current = state;
     tracker->watchers = w->next;
-    if (grpc_connectivity_state_trace) {
+    if (GRPC_TRACER_ON(grpc_connectivity_state_trace)) {
       gpr_log(GPR_DEBUG, "NOTIFY: %p %s: %p", tracker, tracker->name,
               w->notify);
     }
diff --git a/src/core/lib/transport/connectivity_state.h b/src/core/lib/transport/connectivity_state.h
index c9604c34dd..cdc2930c11 100644
--- a/src/core/lib/transport/connectivity_state.h
+++ b/src/core/lib/transport/connectivity_state.h
@@ -35,6 +35,7 @@
 #define GRPC_CORE_LIB_TRANSPORT_CONNECTIVITY_STATE_H
 
 #include <grpc/grpc.h>
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 
 typedef struct grpc_connectivity_state_watcher {
@@ -57,7 +58,7 @@ typedef struct {
   char *name;
 } grpc_connectivity_state_tracker;
 
-extern int grpc_connectivity_state_trace;
+extern grpc_tracer_flag grpc_connectivity_state_trace;
 
 /** enum --> string conversion */
 const char *grpc_connectivity_state_name(grpc_connectivity_state state);
diff --git a/src/core/tsi/fake_transport_security.c b/src/core/tsi/fake_transport_security.c
index 1836beefc4..4925d19f96 100644
--- a/src/core/tsi/fake_transport_security.c
+++ b/src/core/tsi/fake_transport_security.c
@@ -396,7 +396,7 @@ static tsi_result fake_handshaker_get_bytes_to_send_to_peer(
     if (next_message_to_send > TSI_FAKE_HANDSHAKE_MESSAGE_MAX) {
       next_message_to_send = TSI_FAKE_HANDSHAKE_MESSAGE_MAX;
     }
-    if (tsi_tracing_enabled) {
+    if (GRPC_TRACER_ON(tsi_tracing_enabled)) {
       gpr_log(GPR_INFO, "%s prepared %s.",
               impl->is_client ? "Client" : "Server",
               tsi_fake_handshake_message_to_string(impl->next_message_to_send));
@@ -408,7 +408,7 @@ static tsi_result fake_handshaker_get_bytes_to_send_to_peer(
   if (!impl->is_client &&
       impl->next_message_to_send == TSI_FAKE_HANDSHAKE_MESSAGE_MAX) {
     /* We're done. */
-    if (tsi_tracing_enabled) {
+    if (GRPC_TRACER_ON(tsi_tracing_enabled)) {
       gpr_log(GPR_INFO, "Server is done.");
     }
     impl->result = TSI_OK;
@@ -445,7 +445,7 @@ static tsi_result fake_handshaker_process_bytes_from_peer(
             tsi_fake_handshake_message_to_string(received_msg),
             tsi_fake_handshake_message_to_string(expected_msg));
   }
-  if (tsi_tracing_enabled) {
+  if (GRPC_TRACER_ON(tsi_tracing_enabled)) {
     gpr_log(GPR_INFO, "%s received %s.", impl->is_client ? "Client" : "Server",
             tsi_fake_handshake_message_to_string(received_msg));
   }
@@ -453,7 +453,7 @@ static tsi_result fake_handshaker_process_bytes_from_peer(
   impl->needs_incoming_message = 0;
   if (impl->next_message_to_send == TSI_FAKE_HANDSHAKE_MESSAGE_MAX) {
     /* We're done. */
-    if (tsi_tracing_enabled) {
+    if (GRPC_TRACER_ON(tsi_tracing_enabled)) {
       gpr_log(GPR_INFO, "%s is done.", impl->is_client ? "Client" : "Server");
     }
     impl->result = TSI_OK;
diff --git a/src/core/tsi/ssl_transport_security.c b/src/core/tsi/ssl_transport_security.c
index e1d634a1fa..59fd2b1c93 100644
--- a/src/core/tsi/ssl_transport_security.c
+++ b/src/core/tsi/ssl_transport_security.c
@@ -180,7 +180,7 @@ static const char *ssl_error_string(int error) {
 /* TODO(jboeuf): Remove when we are past the debugging phase with this code. */
 static void ssl_log_where_info(const SSL *ssl, int where, int flag,
                                const char *msg) {
-  if ((where & flag) && tsi_tracing_enabled) {
+  if ((where & flag) && GRPC_TRACER_ON(tsi_tracing_enabled)) {
     gpr_log(GPR_INFO, "%20.20s - %30.30s  - %5.10s", msg,
             SSL_state_string_long(ssl), SSL_state_string(ssl));
   }
diff --git a/src/core/tsi/transport_security.c b/src/core/tsi/transport_security.c
index b11c00c43c..4efcf8f43d 100644
--- a/src/core/tsi/transport_security.c
+++ b/src/core/tsi/transport_security.c
@@ -41,7 +41,7 @@
 
 /* --- Tracing. --- */
 
-int tsi_tracing_enabled = 0;
+grpc_tracer_flag tsi_tracing_enabled = GRPC_TRACER_INITIALIZER(false);
 
 /* --- tsi_result common implementation. --- */
 
diff --git a/src/core/tsi/transport_security.h b/src/core/tsi/transport_security.h
index a4c9cbc001..2422f92076 100644
--- a/src/core/tsi/transport_security.h
+++ b/src/core/tsi/transport_security.h
@@ -36,13 +36,14 @@
 
 #include <stdbool.h>
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/tsi/transport_security_interface.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-extern int tsi_tracing_enabled;
+extern grpc_tracer_flag tsi_tracing_enabled;
 
 /* Base for tsi_frame_protector implementations.
    See transport_security_interface.h for documentation. */
diff --git a/src/core/tsi/transport_security_interface.h b/src/core/tsi/transport_security_interface.h
index f2112b62b6..8a3fff6a17 100644
--- a/src/core/tsi/transport_security_interface.h
+++ b/src/core/tsi/transport_security_interface.h
@@ -37,6 +37,8 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+#include "src/core/lib/debug/trace.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -73,8 +75,7 @@ const char *tsi_result_to_string(tsi_result result);
 
 /* --- tsi tracing --- */
 
-/* Set this early to avoid races */
-extern int tsi_tracing_enabled;
+extern grpc_tracer_flag tsi_tracing_enabled;
 
 /* --- tsi_frame_protector object ---