Merge branch 'master' of https://github.com/Vizerai/grpc into intrusive_hash_map

40 files changed, 1853 insertions, 687 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..f2f27b9175 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;
@@ -914,16 +909,18 @@ 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);
+    gpr_atm_no_barrier_store(&calld->subchannel_call, (gpr_atm)CANCELLED_CALL);
     fail_locked(exec_ctx, calld,
-                GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
-                    "Failed to create subchannel", &error, 1));
+                error == GRPC_ERROR_NONE
+                    ? GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+                          "Call dropped by load balancing policy")
+                    : GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
+                          "Failed to create subchannel", &error, 1));
   } else if (GET_CALL(calld) == CANCELLED_CALL) {
     /* already cancelled before subchannel became ready */
     grpc_error *cancellation_error =
@@ -944,7 +941,8 @@ 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 +971,7 @@ 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 +983,8 @@ 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 +996,49 @@ 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 +1061,7 @@ 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 +1074,8 @@ 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 +1094,11 @@ 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 +1150,13 @@ 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 +1166,9 @@ 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");
@@ -1183,24 +1179,34 @@ 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");
+      if (calld->connected_subchannel == NULL) {
+        gpr_atm_no_barrier_store(&calld->subchannel_call,
+                                 (gpr_atm)CANCELLED_CALL);
+        grpc_error *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+            "Call dropped by load balancing policy");
+        fail_locked(exec_ctx, calld, GRPC_ERROR_REF(error));
+        grpc_transport_stream_op_batch_finish_with_failure(exec_ctx, op, error);
+        return;  // Early out.
+      }
     } else {
       grpc_polling_entity_add_to_pollset_set(exec_ctx, calld->pollent,
                                              chand->interested_parties);
     }
   }
   /* 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 +1355,18 @@ 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 +1462,12 @@ 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..fb4aa084a6 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 */
@@ -153,9 +149,13 @@ void grpc_lb_policy_init(grpc_lb_policy *policy,
 
 /** Finds an appropriate subchannel for a call, based on \a pick_args.
 
-    \a target will be set to the selected subchannel, or NULL on failure.
+    \a target will be set to the selected subchannel, or NULL on failure
+    or when the LB policy decides to drop the call.
+
     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 +167,7 @@ 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 9e158a94ad..d2a2856a18 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;
@@ -305,6 +327,11 @@ typedef struct glb_lb_policy {
    * response has arrived. */
   grpc_grpclb_serverlist *serverlist;
 
+  /** Index into serverlist for next pick.
+   * If the server at this index is a drop, we return a drop.
+   * Otherwise, we delegate to the RR policy. */
+  size_t serverlist_index;
+
   /** list of picks that are waiting on RR's policy connectivity */
   pending_pick *pending_picks;
 
@@ -316,6 +343,10 @@ 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 +379,23 @@ 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 */
@@ -359,6 +407,9 @@ struct rr_connectivity_data {
 
 static bool is_server_valid(const grpc_grpclb_server *server, size_t idx,
                             bool log) {
+  if (server->drop_for_rate_limiting || server->drop_for_load_balancing) {
+    return false;
+  }
   const grpc_grpclb_ip_address *ip = &server->ip_address;
   if (server->port >> 16 != 0) {
     if (log) {
@@ -368,7 +419,6 @@ static bool is_server_valid(const grpc_grpclb_server *server, size_t idx,
     }
     return false;
   }
-
   if (ip->size != 4 && ip->size != 16) {
     if (log) {
       gpr_log(GPR_ERROR,
@@ -402,11 +452,12 @@ static const grpc_lb_user_data_vtable lb_token_vtable = {
 
 static void parse_server(const grpc_grpclb_server *server,
                          grpc_resolved_address *addr) {
+  memset(addr, 0, sizeof(*addr));
+  if (server->drop_for_rate_limiting || server->drop_for_load_balancing) return;
   const uint16_t netorder_port = htons((uint16_t)server->port);
   /* the addresses are given in binary format (a in(6)_addr struct) in
    * server->ip_address.bytes. */
   const grpc_grpclb_ip_address *ip = &server->ip_address;
-  memset(addr, 0, sizeof(*addr));
   if (ip->size == 4) {
     addr->len = sizeof(struct sockaddr_in);
     struct sockaddr_in *addr4 = (struct sockaddr_in *)&addr->addr;
@@ -531,7 +582,7 @@ 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),
@@ -543,31 +594,74 @@ static bool update_lb_connectivity_status_locked(
   return true;
 }
 
-/* perform a pick over \a rr_policy. Given that a pick can return immediately
- * (ignoring its completion callback) we need to perform the cleanups this
- * callback would be otherwise resposible for */
+/* Perform a pick over \a glb_policy->rr_policy. Given that a pick can return
+ * immediately (ignoring its completion callback), we need to perform the
+ * cleanups this callback would otherwise be resposible for.
+ * If \a force_async is true, then we will manually schedule the
+ * completion callback even if the pick is available immediately. */
 static bool pick_from_internal_rr_locked(
-    grpc_exec_ctx *exec_ctx, grpc_lb_policy *rr_policy,
-    const grpc_lb_policy_pick_args *pick_args,
+    grpc_exec_ctx *exec_ctx, glb_lb_policy *glb_policy,
+    const grpc_lb_policy_pick_args *pick_args, bool force_async,
     grpc_connected_subchannel **target, wrapped_rr_closure_arg *wc_arg) {
-  GPR_ASSERT(rr_policy != NULL);
+  // Look at the index into the serverlist to see if we should drop this call.
+  grpc_grpclb_server *server =
+      glb_policy->serverlist->servers[glb_policy->serverlist_index++];
+  if (glb_policy->serverlist_index == glb_policy->serverlist->num_servers) {
+    glb_policy->serverlist_index = 0;  // Wrap-around.
+  }
+  if (server->drop_for_rate_limiting || server->drop_for_load_balancing) {
+    // Not using the RR policy, so unref it.
+    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
+      gpr_log(GPR_INFO, "Unreffing RR for drop (0x%" PRIxPTR ")",
+              (intptr_t)wc_arg->rr_policy);
+    }
+    GRPC_LB_POLICY_UNREF(exec_ctx, wc_arg->rr_policy, "glb_pick_sync");
+    // Update client load reporting stats to indicate the number of
+    // dropped calls.  Note that we have to do this here instead of in
+    // the client_load_reporting filter, because we do not create a
+    // subchannel call (and therefore no client_load_reporting filter)
+    // for dropped calls.
+    grpc_grpclb_client_stats_add_call_started(wc_arg->client_stats);
+    grpc_grpclb_client_stats_add_call_finished(
+        server->drop_for_rate_limiting, server->drop_for_load_balancing,
+        false /* failed_to_send */, false /* known_received */,
+        wc_arg->client_stats);
+    grpc_grpclb_client_stats_unref(wc_arg->client_stats);
+    if (force_async) {
+      GPR_ASSERT(wc_arg->wrapped_closure != NULL);
+      grpc_closure_sched(exec_ctx, wc_arg->wrapped_closure, GRPC_ERROR_NONE);
+      gpr_free(wc_arg->free_when_done);
+      return false;
+    }
+    gpr_free(wc_arg->free_when_done);
+    return true;
+  }
+  // Pick via the RR policy.
   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, wc_arg->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);
     }
     GRPC_LB_POLICY_UNREF(exec_ctx, wc_arg->rr_policy, "glb_pick_sync");
-
     /* add the load reporting initial metadata */
     initial_metadata_add_lb_token(exec_ctx, pick_args->initial_metadata,
                                   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;
+    if (force_async) {
+      GPR_ASSERT(wc_arg->wrapped_closure != NULL);
+      grpc_closure_sched(exec_ctx, wc_arg->wrapped_closure, GRPC_ERROR_NONE);
+      gpr_free(wc_arg->free_when_done);
+      return false;
+    }
+    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 +731,7 @@ 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 +741,7 @@ 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);
   }
@@ -690,12 +784,14 @@ 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);
     }
-    pick_from_internal_rr_locked(exec_ctx, glb_policy->rr_policy,
-                                 &pp->pick_args, pp->target,
+    pick_from_internal_rr_locked(exec_ctx, glb_policy, &pp->pick_args,
+                                 true /* force_async */, pp->target,
                                  &pp->wrapped_on_complete_arg);
   }
 
@@ -704,7 +800,7 @@ 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 +953,29 @@ 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 +989,8 @@ 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 +1006,9 @@ 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 +1125,8 @@ 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 +1138,10 @@ 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);
     }
@@ -1039,20 +1153,25 @@ 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;
     wc_arg->free_when_done = wc_arg;
-    pick_done = pick_from_internal_rr_locked(exec_ctx, glb_policy->rr_policy,
-                                             pick_args, target, wc_arg);
+    pick_done =
+        pick_from_internal_rr_locked(exec_ctx, glb_policy, pick_args,
+                                     false /* force_async */, 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 +1212,104 @@ 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 +1324,24 @@ 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 +1353,9 @@ 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 +1369,10 @@ 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 +1386,10 @@ 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 +1402,7 @@ 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 +1418,27 @@ 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 +1470,19 @@ 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 +1498,91 @@ 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;
+            glb_policy->serverlist_index = 0;
+            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(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 +1610,7 @@ 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 +1627,7 @@ 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 +1646,7 @@ 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 +1694,29 @@ 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..90e7c2efe5 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
@@ -37,58 +37,83 @@
 
 #include <grpc/support/alloc.h>
 
+/* invoked once for every Server in ServerList */
+static bool count_serverlist(pb_istream_t *stream, const pb_field_t *field,
+                             void **arg) {
+  grpc_grpclb_serverlist *sl = *arg;
+  grpc_grpclb_server server;
+  if (!pb_decode(stream, grpc_lb_v1_Server_fields, &server)) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
+    return false;
+  }
+  ++sl->num_servers;
+  return true;
+}
+
 typedef struct decode_serverlist_arg {
-  /* The first pass counts the number of servers in the server list. The second
-   * one allocates and decodes. */
-  bool first_pass;
   /* The decoding callback is invoked once per server in serverlist. Remember
    * which index of the serverlist are we currently decoding */
   size_t decoding_idx;
-  /* Populated after the first pass. Number of server in the input serverlist */
-  size_t num_servers;
   /* The decoded serverlist */
-  grpc_grpclb_server **servers;
+  grpc_grpclb_serverlist *serverlist;
 } decode_serverlist_arg;
 
 /* invoked once for every Server in ServerList */
 static bool decode_serverlist(pb_istream_t *stream, const pb_field_t *field,
                               void **arg) {
   decode_serverlist_arg *dec_arg = *arg;
-  if (dec_arg->first_pass) { /* count how many server do we have */
-    grpc_grpclb_server server;
-    if (!pb_decode(stream, grpc_lb_v1_Server_fields, &server)) {
-      gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
-      return false;
-    }
-    dec_arg->num_servers++;
-  } else { /* second pass. Actually decode. */
-    grpc_grpclb_server *server = gpr_zalloc(sizeof(grpc_grpclb_server));
-    GPR_ASSERT(dec_arg->num_servers > 0);
-    if (dec_arg->decoding_idx == 0) { /* first iteration of second pass */
-      dec_arg->servers =
-          gpr_malloc(sizeof(grpc_grpclb_server *) * dec_arg->num_servers);
-    }
-    if (!pb_decode(stream, grpc_lb_v1_Server_fields, server)) {
-      gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
-      return false;
-    }
-    dec_arg->servers[dec_arg->decoding_idx++] = server;
+  GPR_ASSERT(dec_arg->serverlist->num_servers >= dec_arg->decoding_idx);
+  grpc_grpclb_server *server = gpr_zalloc(sizeof(grpc_grpclb_server));
+  if (!pb_decode(stream, grpc_lb_v1_Server_fields, server)) {
+    gpr_free(server);
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
+    return false;
   }
-
+  dec_arg->serverlist->servers[dec_arg->decoding_idx++] = server;
   return true;
 }
 
 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 +147,9 @@ 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,
@@ -132,36 +160,38 @@ grpc_grpclb_initial_response *grpc_grpclb_initial_response_parse(
 
 grpc_grpclb_serverlist *grpc_grpclb_response_parse_serverlist(
     grpc_slice encoded_grpc_grpclb_response) {
-  bool status;
-  decode_serverlist_arg arg;
   pb_istream_t stream =
       pb_istream_from_buffer(GRPC_SLICE_START_PTR(encoded_grpc_grpclb_response),
                              GRPC_SLICE_LENGTH(encoded_grpc_grpclb_response));
   pb_istream_t stream_at_start = stream;
+  grpc_grpclb_serverlist *sl = gpr_zalloc(sizeof(grpc_grpclb_serverlist));
   grpc_grpclb_response res;
   memset(&res, 0, sizeof(grpc_grpclb_response));
-  memset(&arg, 0, sizeof(decode_serverlist_arg));
-
-  res.server_list.servers.funcs.decode = decode_serverlist;
-  res.server_list.servers.arg = &arg;
-  arg.first_pass = true;
-  status = pb_decode(&stream, grpc_lb_v1_LoadBalanceResponse_fields, &res);
+  // First pass: count number of servers.
+  res.server_list.servers.funcs.decode = count_serverlist;
+  res.server_list.servers.arg = sl;
+  bool status = pb_decode(&stream, grpc_lb_v1_LoadBalanceResponse_fields, &res);
   if (!status) {
+    gpr_free(sl);
     gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
     return NULL;
   }
-
-  arg.first_pass = false;
-  status =
-      pb_decode(&stream_at_start, grpc_lb_v1_LoadBalanceResponse_fields, &res);
-  if (!status) {
-    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
-    return NULL;
+  // Second pass: populate servers.
+  if (sl->num_servers > 0) {
+    sl->servers = gpr_zalloc(sizeof(grpc_grpclb_server *) * sl->num_servers);
+    decode_serverlist_arg decode_arg;
+    memset(&decode_arg, 0, sizeof(decode_arg));
+    decode_arg.serverlist = sl;
+    res.server_list.servers.funcs.decode = decode_serverlist;
+    res.server_list.servers.arg = &decode_arg;
+    status = pb_decode(&stream_at_start, grpc_lb_v1_LoadBalanceResponse_fields,
+                       &res);
+    if (!status) {
+      grpc_grpclb_destroy_serverlist(sl);
+      gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
+      return NULL;
+    }
   }
-
-  grpc_grpclb_serverlist *sl = gpr_zalloc(sizeof(grpc_grpclb_serverlist));
-  sl->num_servers = arg.num_servers;
-  sl->servers = arg.servers;
   if (res.server_list.has_expiration_interval) {
     sl->expiration_interval = res.server_list.expiration_interval;
   }
@@ -195,7 +225,7 @@ grpc_grpclb_serverlist *grpc_grpclb_serverlist_copy(
 
 bool grpc_grpclb_serverlist_equals(const grpc_grpclb_serverlist *lhs,
                                    const grpc_grpclb_serverlist *rhs) {
-  if ((lhs == NULL) || (rhs == NULL)) {
+  if (lhs == NULL || rhs == NULL) {
     return false;
   }
   if (lhs->num_servers != rhs->num_servers) {
@@ -243,6 +273,15 @@ 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..7f596ce1f1 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"
 
@@ -50,7 +51,7 @@ typedef grpc_lb_v1_LoadBalanceRequest grpc_grpclb_request;
 typedef grpc_lb_v1_InitialLoadBalanceResponse grpc_grpclb_initial_response;
 typedef grpc_lb_v1_Server grpc_grpclb_server;
 typedef grpc_lb_v1_Duration grpc_grpclb_duration;
-typedef struct grpc_grpclb_serverlist {
+typedef struct {
   grpc_grpclb_server **servers;
   size_t num_servers;
   grpc_grpclb_duration expiration_interval;
@@ -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..7ee6ffb787 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.
  *
@@ -99,26 +99,13 @@ typedef struct pending_pick {
   grpc_closure *on_complete;
 } pending_pick;
 
-/** List of subchannels in a connectivity READY state */
-typedef struct ready_list {
-  grpc_subchannel *subchannel;
-  /* references namesake entry in subchannel_data */
-  void *user_data;
-  struct ready_list *next;
-  struct ready_list *prev;
-} ready_list;
-
 typedef struct {
-  /** index within policy->subchannels */
-  size_t index;
   /** backpointer to owning policy */
   round_robin_lb_policy *policy;
   /** subchannel itself */
   grpc_subchannel *subchannel;
   /** notification that connectivity has changed on subchannel */
   grpc_closure connectivity_changed_closure;
-  /** this subchannels current position in subchannel->ready_list */
-  ready_list *ready_list_node;
   /** last observed connectivity. Not updated by
    * \a grpc_subchannel_notify_on_state_change. Used to determine the previous
    * state while processing the new state in \a rr_connectivity_changed */
@@ -126,6 +113,10 @@ typedef struct {
   /** current connectivity state. Updated by \a
    * grpc_subchannel_notify_on_state_change */
   grpc_connectivity_state curr_connectivity_state;
+  /** connectivity state to be updated by the watcher, not guarded by
+   * the combiner.  Will be moved to curr_connectivity_state inside of
+   * the combiner by rr_connectivity_changed_locked(). */
+  grpc_connectivity_state pending_connectivity_state_unsafe;
   /** the subchannel's target user data */
   void *user_data;
   /** vtable to operate over \a user_data */
@@ -141,182 +132,106 @@ struct round_robin_lb_policy {
 
   /** all our subchannels */
   size_t num_subchannels;
-  subchannel_data **subchannels;
+  subchannel_data *subchannels;
 
-  /** how many subchannels are in TRANSIENT_FAILURE */
+  /** how many subchannels are in state READY */
+  size_t num_ready;
+  /** how many subchannels are in state TRANSIENT_FAILURE */
   size_t num_transient_failures;
-  /** how many subchannels are IDLE */
+  /** how many subchannels are in state IDLE */
   size_t num_idle;
 
   /** have we started picking? */
-  int started_picking;
+  bool started_picking;
   /** are we shutting down? */
-  int shutdown;
+  bool shutdown;
   /** List of picks that are waiting on connectivity */
   pending_pick *pending_picks;
 
   /** our connectivity state tracker */
   grpc_connectivity_state_tracker state_tracker;
 
-  /** (Dummy) root of the doubly linked list containing READY subchannels */
-  ready_list ready_list;
-  /** Last pick from the ready list. */
-  ready_list *ready_list_last_pick;
+  // Index into subchannels for last pick.
+  size_t last_ready_subchannel_index;
 };
 
-/** Returns the next subchannel from the connected list or NULL if the list is
- * empty.
+/** Returns the index into p->subchannels of the next subchannel in
+ * READY state, or p->num_subchannels if no subchannel is READY.
  *
- * Note that this function does *not* advance p->ready_list_last_pick. Use \a
- * advance_last_picked_locked() for that. */
-static ready_list *peek_next_connected_locked(const round_robin_lb_policy *p) {
-  ready_list *selected;
-  selected = p->ready_list_last_pick->next;
-
-  while (selected != NULL) {
-    if (selected == &p->ready_list) {
-      GPR_ASSERT(selected->subchannel == NULL);
-      /* skip dummy root */
-      selected = selected->next;
-    } else {
-      GPR_ASSERT(selected->subchannel != NULL);
-      return selected;
-    }
+ * Note that this function does *not* update p->last_ready_subchannel_index.
+ * The caller must do that if it returns a pick. */
+static size_t get_next_ready_subchannel_index_locked(
+    const round_robin_lb_policy *p) {
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+    gpr_log(GPR_INFO,
+            "[RR: %p] getting next ready subchannel, "
+            "last_ready_subchannel_index=%lu",
+            p, (unsigned long)p->last_ready_subchannel_index);
   }
-  return NULL;
-}
-
-/** Advance the \a ready_list picking head. */
-static void advance_last_picked_locked(round_robin_lb_policy *p) {
-  if (p->ready_list_last_pick->next != NULL) { /* non-empty list */
-    p->ready_list_last_pick = p->ready_list_last_pick->next;
-    if (p->ready_list_last_pick == &p->ready_list) {
-      /* skip dummy root */
-      p->ready_list_last_pick = p->ready_list_last_pick->next;
+  for (size_t i = 0; i < p->num_subchannels; ++i) {
+    const size_t index =
+        (i + p->last_ready_subchannel_index + 1) % p->num_subchannels;
+    if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+      gpr_log(GPR_DEBUG, "[RR %p] checking index %lu: state=%d", p,
+              (unsigned long)index,
+              p->subchannels[index].curr_connectivity_state);
+    }
+    if (p->subchannels[index].curr_connectivity_state == GRPC_CHANNEL_READY) {
+      if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+        gpr_log(GPR_DEBUG, "[RR %p] found next ready subchannel at index %lu",
+                p, (unsigned long)index);
+      }
+      return index;
     }
-  } else { /* should be an empty list */
-    GPR_ASSERT(p->ready_list_last_pick == &p->ready_list);
-  }
-
-  if (grpc_lb_round_robin_trace) {
-    gpr_log(GPR_DEBUG,
-            "[READYLIST, RR: %p] ADVANCED LAST PICK. NOW AT NODE %p (SC %p, "
-            "CSC %p)",
-            (void *)p, (void *)p->ready_list_last_pick,
-            (void *)p->ready_list_last_pick->subchannel,
-            (void *)grpc_subchannel_get_connected_subchannel(
-                p->ready_list_last_pick->subchannel));
-  }
-}
-
-/** Prepends (relative to the root at p->ready_list) the connected subchannel \a
- * csc to the list of ready subchannels. */
-static ready_list *add_connected_sc_locked(round_robin_lb_policy *p,
-                                           subchannel_data *sd) {
-  ready_list *new_elem = gpr_zalloc(sizeof(ready_list));
-  new_elem->subchannel = sd->subchannel;
-  new_elem->user_data = sd->user_data;
-  if (p->ready_list.prev == NULL) {
-    /* first element */
-    new_elem->next = &p->ready_list;
-    new_elem->prev = &p->ready_list;
-    p->ready_list.next = new_elem;
-    p->ready_list.prev = new_elem;
-  } else {
-    new_elem->next = &p->ready_list;
-    new_elem->prev = p->ready_list.prev;
-    p->ready_list.prev->next = new_elem;
-    p->ready_list.prev = new_elem;
   }
-  if (grpc_lb_round_robin_trace) {
-    gpr_log(GPR_DEBUG, "[READYLIST] ADDING NODE %p (Conn. SC %p)",
-            (void *)new_elem, (void *)sd->subchannel);
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+    gpr_log(GPR_DEBUG, "[RR %p] no subchannels in ready state", p);
   }
-  return new_elem;
+  return p->num_subchannels;
 }
 
-/** Removes \a node from the list of connected subchannels */
-static void remove_disconnected_sc_locked(round_robin_lb_policy *p,
-                                          ready_list *node) {
-  if (node == NULL) {
-    return;
-  }
-  if (node == p->ready_list_last_pick) {
-    p->ready_list_last_pick = p->ready_list_last_pick->prev;
-  }
-
-  /* removing last item */
-  if (node->next == &p->ready_list && node->prev == &p->ready_list) {
-    GPR_ASSERT(p->ready_list.next == node);
-    GPR_ASSERT(p->ready_list.prev == node);
-    p->ready_list.next = NULL;
-    p->ready_list.prev = NULL;
-  } else {
-    node->prev->next = node->next;
-    node->next->prev = node->prev;
-  }
-
-  if (grpc_lb_round_robin_trace) {
-    gpr_log(GPR_DEBUG, "[READYLIST] REMOVED NODE %p (SC %p)", (void *)node,
-            (void *)node->subchannel);
+// Sets p->last_ready_subchannel_index to last_ready_index.
+static void update_last_ready_subchannel_index_locked(round_robin_lb_policy *p,
+                                                      size_t last_ready_index) {
+  GPR_ASSERT(last_ready_index < p->num_subchannels);
+  p->last_ready_subchannel_index = last_ready_index;
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+    gpr_log(GPR_DEBUG,
+            "[RR: %p] setting last_ready_subchannel_index=%lu (SC %p, CSC %p)",
+            (void *)p, (unsigned long)last_ready_index,
+            (void *)p->subchannels[last_ready_index].subchannel,
+            (void *)grpc_subchannel_get_connected_subchannel(
+                p->subchannels[last_ready_index].subchannel));
   }
-
-  node->next = NULL;
-  node->prev = NULL;
-  node->subchannel = NULL;
-
-  gpr_free(node);
-}
-
-static bool is_ready_list_empty(round_robin_lb_policy *p) {
-  return p->ready_list.prev == NULL;
 }
 
 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);
   }
-
   for (size_t i = 0; i < p->num_subchannels; i++) {
-    subchannel_data *sd = p->subchannels[i];
-    GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "rr_destroy");
-    if (sd->user_data != NULL) {
-      GPR_ASSERT(sd->user_data_vtable != NULL);
-      sd->user_data_vtable->destroy(exec_ctx, sd->user_data);
+    subchannel_data *sd = &p->subchannels[i];
+    if (sd->subchannel != NULL) {
+      GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "rr_destroy");
+      if (sd->user_data != NULL) {
+        GPR_ASSERT(sd->user_data_vtable != NULL);
+        sd->user_data_vtable->destroy(exec_ctx, sd->user_data);
+      }
     }
-    gpr_free(sd);
   }
-
   grpc_connectivity_state_destroy(exec_ctx, &p->state_tracker);
   gpr_free(p->subchannels);
-
-  elem = p->ready_list.next;
-  while (elem != NULL && elem != &p->ready_list) {
-    ready_list *tmp;
-    tmp = elem->next;
-    elem->next = NULL;
-    elem->prev = NULL;
-    elem->subchannel = NULL;
-    gpr_free(elem);
-    elem = tmp;
-  }
-
   gpr_free(p);
 }
 
 static void rr_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   round_robin_lb_policy *p = (round_robin_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);
   }
-
-  p->shutdown = 1;
+  p->shutdown = true;
+  pending_pick *pp;
   while ((pp = p->pending_picks)) {
     p->pending_picks = pp->next;
     *pp->target = NULL;
@@ -328,10 +243,13 @@ static void rr_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   grpc_connectivity_state_set(
       exec_ctx, &p->state_tracker, GRPC_CHANNEL_SHUTDOWN,
       GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"), "rr_shutdown");
-  for (i = 0; i < p->num_subchannels; i++) {
-    subchannel_data *sd = p->subchannels[i];
-    grpc_subchannel_notify_on_state_change(exec_ctx, sd->subchannel, NULL, NULL,
-                                           &sd->connectivity_changed_closure);
+  for (size_t i = 0; i < p->num_subchannels; i++) {
+    subchannel_data *sd = &p->subchannels[i];
+    if (sd->subchannel != NULL) {
+      grpc_subchannel_notify_on_state_change(exec_ctx, sd->subchannel, NULL,
+                                             NULL,
+                                             &sd->connectivity_changed_closure);
+    }
   }
 }
 
@@ -339,8 +257,7 @@ static void rr_cancel_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                                   grpc_connected_subchannel **target,
                                   grpc_error *error) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
-  pending_pick *pp;
-  pp = p->pending_picks;
+  pending_pick *pp = p->pending_picks;
   p->pending_picks = NULL;
   while (pp != NULL) {
     pending_pick *next = pp->next;
@@ -364,8 +281,7 @@ static void rr_cancel_picks_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                                    uint32_t initial_metadata_flags_eq,
                                    grpc_error *error) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
-  pending_pick *pp;
-  pp = p->pending_picks;
+  pending_pick *pp = p->pending_picks;
   p->pending_picks = NULL;
   while (pp != NULL) {
     pending_pick *next = pp->next;
@@ -387,21 +303,16 @@ static void rr_cancel_picks_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
 
 static void start_picking_locked(grpc_exec_ctx *exec_ctx,
                                  round_robin_lb_policy *p) {
-  size_t i;
-  p->started_picking = 1;
-
-  for (i = 0; i < p->num_subchannels; i++) {
-    subchannel_data *sd = p->subchannels[i];
-    /* use some sentinel value outside of the range of grpc_connectivity_state
-     * to signal an undefined previous state. We won't be referring to this
-     * value again and it'll be overwritten after the first call to
-     * rr_connectivity_changed */
-    sd->prev_connectivity_state = GRPC_CHANNEL_INIT;
-    sd->curr_connectivity_state = GRPC_CHANNEL_IDLE;
-    GRPC_LB_POLICY_WEAK_REF(&p->base, "rr_connectivity");
-    grpc_subchannel_notify_on_state_change(
-        exec_ctx, sd->subchannel, p->base.interested_parties,
-        &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
+  p->started_picking = true;
+  for (size_t i = 0; i < p->num_subchannels; i++) {
+    subchannel_data *sd = &p->subchannels[i];
+    if (sd->subchannel != NULL) {
+      GRPC_LB_POLICY_WEAK_REF(&p->base, "rr_connectivity");
+      grpc_subchannel_notify_on_state_change(
+          exec_ctx, sd->subchannel, p->base.interested_parties,
+          &sd->pending_connectivity_state_unsafe,
+          &sd->connectivity_changed_closure);
+    }
   }
 }
 
@@ -414,39 +325,36 @@ 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);
   }
-
-  if ((selected = peek_next_connected_locked(p))) {
+  const size_t next_ready_index = get_next_ready_subchannel_index_locked(p);
+  if (next_ready_index < p->num_subchannels) {
     /* readily available, report right away */
+    subchannel_data *sd = &p->subchannels[next_ready_index];
     *target = GRPC_CONNECTED_SUBCHANNEL_REF(
-        grpc_subchannel_get_connected_subchannel(selected->subchannel),
-        "rr_picked");
-
+        grpc_subchannel_get_connected_subchannel(sd->subchannel), "rr_picked");
     if (user_data != NULL) {
-      *user_data = selected->user_data;
+      *user_data = sd->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);
+              "[RR PICK] TARGET <-- CONNECTED SUBCHANNEL %p (INDEX %lu)",
+              (void *)*target, (unsigned long)next_ready_index);
     }
     /* only advance the last picked pointer if the selection was used */
-    advance_last_picked_locked(p);
+    update_last_ready_subchannel_index_locked(p, next_ready_index);
     return 1;
   } else {
     /* no pick currently available. Save for later in list of pending picks */
     if (!p->started_picking) {
       start_picking_locked(exec_ctx, p);
     }
-    pp = gpr_malloc(sizeof(*pp));
+    pending_pick *pp = gpr_malloc(sizeof(*pp));
     pp->next = p->pending_picks;
     pp->target = target;
     pp->on_complete = on_complete;
@@ -457,25 +365,31 @@ static int rr_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
   }
 }
 
-static void update_state_counters(subchannel_data *sd) {
+static void update_state_counters_locked(subchannel_data *sd) {
   round_robin_lb_policy *p = sd->policy;
-
-  /* update p->num_transient_failures (resp. p->num_idle): if the previous
-   * state was TRANSIENT_FAILURE (resp. IDLE), decrement
-   * p->num_transient_failures (resp. p->num_idle). */
-  if (sd->prev_connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
+  if (sd->prev_connectivity_state == GRPC_CHANNEL_READY) {
+    GPR_ASSERT(p->num_ready > 0);
+    --p->num_ready;
+  } else if (sd->prev_connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
     GPR_ASSERT(p->num_transient_failures > 0);
     --p->num_transient_failures;
   } else if (sd->prev_connectivity_state == GRPC_CHANNEL_IDLE) {
     GPR_ASSERT(p->num_idle > 0);
     --p->num_idle;
   }
+  if (sd->curr_connectivity_state == GRPC_CHANNEL_READY) {
+    ++p->num_ready;
+  } else if (sd->curr_connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
+    ++p->num_transient_failures;
+  } else if (sd->curr_connectivity_state == GRPC_CHANNEL_IDLE) {
+    ++p->num_idle;
+  }
 }
 
 /* sd is the subchannel_data associted with the updated subchannel.
  * shutdown_error will only be used upon policy transition to TRANSIENT_FAILURE
  * or SHUTDOWN */
-static grpc_connectivity_state update_lb_connectivity_status(
+static grpc_connectivity_state update_lb_connectivity_status_locked(
     grpc_exec_ctx *exec_ctx, subchannel_data *sd, grpc_error *error) {
   /* In priority order. The first rule to match terminates the search (ie, if we
    * are on rule n, all previous rules were unfulfilled).
@@ -497,7 +411,7 @@ static grpc_connectivity_state update_lb_connectivity_status(
    *    CHECK: p->num_idle == p->num_subchannels.
    */
   round_robin_lb_policy *p = sd->policy;
-  if (!is_ready_list_empty(p)) { /* 1) READY */
+  if (p->num_ready > 0) { /* 1) READY */
     grpc_connectivity_state_set(exec_ctx, &p->state_tracker, GRPC_CHANNEL_READY,
                                 GRPC_ERROR_NONE, "rr_ready");
     return GRPC_CHANNEL_READY;
@@ -531,32 +445,62 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
                                            grpc_error *error) {
   subchannel_data *sd = arg;
   round_robin_lb_policy *p = sd->policy;
-  pending_pick *pp;
-
-  GRPC_ERROR_REF(error);
-
+  // Now that we're inside the combiner, copy the pending connectivity
+  // state (which was set by the connectivity state watcher) to
+  // curr_connectivity_state, which is what we use inside of the combiner.
+  sd->curr_connectivity_state = sd->pending_connectivity_state_unsafe;
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+    gpr_log(GPR_DEBUG,
+            "[RR %p] connectivity changed for subchannel %p: "
+            "prev_state=%d new_state=%d",
+            p, sd->subchannel, sd->prev_connectivity_state,
+            sd->curr_connectivity_state);
+  }
+  // If we're shutting down, unref and return.
   if (p->shutdown) {
     GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "rr_connectivity");
-    GRPC_ERROR_UNREF(error);
     return;
   }
-  switch (sd->curr_connectivity_state) {
-    case GRPC_CHANNEL_INIT:
-      GPR_UNREACHABLE_CODE(return );
-    case GRPC_CHANNEL_READY:
-      /* add the newly connected subchannel to the list of connected ones.
-       * Note that it goes to the "end of the line". */
-      sd->ready_list_node = add_connected_sc_locked(p, sd);
+  // Update state counters and determine new overall state.
+  update_state_counters_locked(sd);
+  sd->prev_connectivity_state = sd->curr_connectivity_state;
+  grpc_connectivity_state new_connectivity_state =
+      update_lb_connectivity_status_locked(exec_ctx, sd, GRPC_ERROR_REF(error));
+  // If the new state is SHUTDOWN, unref the subchannel, and if the new
+  // overall state is SHUTDOWN, clean up.
+  if (sd->curr_connectivity_state == GRPC_CHANNEL_SHUTDOWN) {
+    GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "rr_subchannel_shutdown");
+    sd->subchannel = NULL;
+    if (sd->user_data != NULL) {
+      GPR_ASSERT(sd->user_data_vtable != NULL);
+      sd->user_data_vtable->destroy(exec_ctx, sd->user_data);
+    }
+    if (new_connectivity_state == GRPC_CHANNEL_SHUTDOWN) {
+      /* the policy is shutting down. Flush all the pending picks... */
+      pending_pick *pp;
+      while ((pp = p->pending_picks)) {
+        p->pending_picks = pp->next;
+        *pp->target = NULL;
+        grpc_closure_sched(exec_ctx, pp->on_complete, GRPC_ERROR_NONE);
+        gpr_free(pp);
+      }
+    }
+    /* unref the "rr_connectivity" weak ref from start_picking */
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "rr_connectivity");
+  } else {
+    if (sd->curr_connectivity_state == GRPC_CHANNEL_READY) {
       /* at this point we know there's at least one suitable subchannel. Go
        * ahead and pick one and notify the pending suitors in
        * p->pending_picks. This preemtively replicates rr_pick()'s actions. */
-      ready_list *selected = peek_next_connected_locked(p);
-      GPR_ASSERT(selected != NULL);
+      const size_t next_ready_index = get_next_ready_subchannel_index_locked(p);
+      GPR_ASSERT(next_ready_index < p->num_subchannels);
+      subchannel_data *selected = &p->subchannels[next_ready_index];
       if (p->pending_picks != NULL) {
         /* if the selected subchannel is going to be used for the pending
          * picks, update the last picked pointer */
-        advance_last_picked_locked(p);
+        update_last_ready_subchannel_index_locked(p, next_ready_index);
       }
+      pending_pick *pp;
       while ((pp = p->pending_picks)) {
         p->pending_picks = pp->next;
         *pp->target = GRPC_CONNECTED_SUBCHANNEL_REF(
@@ -565,74 +509,22 @@ 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);
+                  "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (INDEX %lu)",
+                  (void *)selected->subchannel,
+                  (unsigned long)next_ready_index);
         }
         grpc_closure_sched(exec_ctx, pp->on_complete, GRPC_ERROR_NONE);
         gpr_free(pp);
       }
-      update_lb_connectivity_status(exec_ctx, sd, error);
-      sd->prev_connectivity_state = sd->curr_connectivity_state;
-      /* renew notification: reuses the "rr_connectivity" weak ref */
-      grpc_subchannel_notify_on_state_change(
-          exec_ctx, sd->subchannel, p->base.interested_parties,
-          &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
-      break;
-    case GRPC_CHANNEL_IDLE:
-      ++p->num_idle;
-    /* fallthrough */
-    case GRPC_CHANNEL_CONNECTING:
-      update_state_counters(sd);
-      update_lb_connectivity_status(exec_ctx, sd, error);
-      sd->prev_connectivity_state = sd->curr_connectivity_state;
-      /* renew notification: reuses the "rr_connectivity" weak ref */
-      grpc_subchannel_notify_on_state_change(
-          exec_ctx, sd->subchannel, p->base.interested_parties,
-          &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
-      break;
-    case GRPC_CHANNEL_TRANSIENT_FAILURE:
-      ++p->num_transient_failures;
-      /* remove from ready list if still present */
-      if (sd->ready_list_node != NULL) {
-        remove_disconnected_sc_locked(p, sd->ready_list_node);
-        sd->ready_list_node = NULL;
-      }
-      update_lb_connectivity_status(exec_ctx, sd, error);
-      sd->prev_connectivity_state = sd->curr_connectivity_state;
-      /* renew notification: reuses the "rr_connectivity" weak ref */
-      grpc_subchannel_notify_on_state_change(
-          exec_ctx, sd->subchannel, p->base.interested_parties,
-          &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
-      break;
-    case GRPC_CHANNEL_SHUTDOWN:
-      update_state_counters(sd);
-      if (sd->ready_list_node != NULL) {
-        remove_disconnected_sc_locked(p, sd->ready_list_node);
-        sd->ready_list_node = NULL;
-      }
-      --p->num_subchannels;
-      GPR_SWAP(subchannel_data *, p->subchannels[sd->index],
-               p->subchannels[p->num_subchannels]);
-      GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "rr_subchannel_shutdown");
-      p->subchannels[sd->index]->index = sd->index;
-      if (update_lb_connectivity_status(exec_ctx, sd, error) ==
-          GRPC_CHANNEL_SHUTDOWN) {
-        /* the policy is shutting down. Flush all the pending picks... */
-        while ((pp = p->pending_picks)) {
-          p->pending_picks = pp->next;
-          *pp->target = NULL;
-          grpc_closure_sched(exec_ctx, pp->on_complete, GRPC_ERROR_NONE);
-          gpr_free(pp);
-        }
-      }
-      gpr_free(sd);
-      /* unref the "rr_connectivity" weak ref from start_picking */
-      GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "rr_connectivity");
-      break;
+    }
+    /* renew notification: reuses the "rr_connectivity" weak ref */
+    grpc_subchannel_notify_on_state_change(
+        exec_ctx, sd->subchannel, p->base.interested_parties,
+        &sd->pending_connectivity_state_unsafe,
+        &sd->connectivity_changed_closure);
   }
-  GRPC_ERROR_UNREF(error);
 }
 
 static grpc_connectivity_state rr_check_connectivity_locked(
@@ -653,10 +545,10 @@ static void rr_notify_on_state_change_locked(grpc_exec_ctx *exec_ctx,
 static void rr_ping_one_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                                grpc_closure *closure) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
-  ready_list *selected;
-  grpc_connected_subchannel *target;
-  if ((selected = peek_next_connected_locked(p))) {
-    target = GRPC_CONNECTED_SUBCHANNEL_REF(
+  const size_t next_ready_index = get_next_ready_subchannel_index_locked(p);
+  if (next_ready_index < p->num_subchannels) {
+    subchannel_data *selected = &p->subchannels[next_ready_index];
+    grpc_connected_subchannel *target = GRPC_CONNECTED_SUBCHANNEL_REF(
         grpc_subchannel_get_connected_subchannel(selected->subchannel),
         "rr_picked");
     grpc_connected_subchannel_ping(exec_ctx, target, closure);
@@ -707,7 +599,7 @@ static grpc_lb_policy *round_robin_create(grpc_exec_ctx *exec_ctx,
   p->subchannels = gpr_zalloc(sizeof(*p->subchannels) * num_addrs);
 
   grpc_subchannel_args sc_args;
-  size_t subchannel_idx = 0;
+  size_t subchannel_index = 0;
   for (size_t i = 0; i < addresses->num_addresses; i++) {
     /* Skip balancer addresses, since we only know how to handle backends. */
     if (addresses->addresses[i].is_balancer) continue;
@@ -723,51 +615,53 @@ 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",
-              (void *)subchannel, address_uri);
+      gpr_log(GPR_DEBUG, "index %lu: Created subchannel %p for address uri %s",
+              (unsigned long)subchannel_index, (void *)subchannel, address_uri);
       gpr_free(address_uri);
     }
     grpc_channel_args_destroy(exec_ctx, new_args);
 
     if (subchannel != NULL) {
-      subchannel_data *sd = gpr_zalloc(sizeof(*sd));
-      p->subchannels[subchannel_idx] = sd;
+      subchannel_data *sd = &p->subchannels[subchannel_index];
       sd->policy = p;
-      sd->index = subchannel_idx;
       sd->subchannel = subchannel;
+      /* use some sentinel value outside of the range of grpc_connectivity_state
+       * to signal an undefined previous state. We won't be referring to this
+       * value again and it'll be overwritten after the first call to
+       * rr_connectivity_changed */
+      sd->prev_connectivity_state = GRPC_CHANNEL_INIT;
+      sd->curr_connectivity_state = GRPC_CHANNEL_IDLE;
       sd->user_data_vtable = addresses->user_data_vtable;
       if (sd->user_data_vtable != NULL) {
         sd->user_data =
             sd->user_data_vtable->copy(addresses->addresses[i].user_data);
       }
-      ++subchannel_idx;
       grpc_closure_init(&sd->connectivity_changed_closure,
                         rr_connectivity_changed_locked, sd,
                         grpc_combiner_scheduler(args->combiner, false));
+      ++subchannel_index;
     }
   }
-  if (subchannel_idx == 0) {
+  if (subchannel_index == 0) {
     /* couldn't create any subchannel. Bail out */
     gpr_free(p->subchannels);
     gpr_free(p);
     return NULL;
   }
-  p->num_subchannels = subchannel_idx;
+  p->num_subchannels = subchannel_index;
 
-  /* The (dummy node) root of the ready list */
-  p->ready_list.subchannel = NULL;
-  p->ready_list.prev = NULL;
-  p->ready_list.next = NULL;
-  p->ready_list_last_pick = &p->ready_list;
+  // Initialize the last pick index to the last subchannel, so that the
+  // first pick will start at the beginning of the list.
+  p->last_ready_subchannel_index = subchannel_index - 1;
 
   grpc_lb_policy_init(&p->base, &round_robin_lb_policy_vtable, args->combiner);
   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/parse_address.c b/src/core/ext/filters/client_channel/parse_address.c
index edc6ce697d..18381eec55 100644
--- a/src/core/ext/filters/client_channel/parse_address.c
+++ b/src/core/ext/filters/client_channel/parse_address.c
@@ -57,11 +57,11 @@ bool grpc_parse_unix(const grpc_uri *uri,
   struct sockaddr_un *un = (struct sockaddr_un *)resolved_addr->addr;
   const size_t maxlen = sizeof(un->sun_path);
   const size_t path_len = strnlen(uri->path, maxlen);
-  if (path_len == maxlen) return 0;
+  if (path_len == maxlen) return false;
   un->sun_family = AF_UNIX;
   strcpy(un->sun_path, uri->path);
   resolved_addr->len = sizeof(*un);
-  return 1;
+  return true;
 }
 
 #else /* GRPC_HAVE_UNIX_SOCKET */
@@ -73,74 +73,65 @@ bool grpc_parse_unix(const grpc_uri *uri,
 
 #endif /* GRPC_HAVE_UNIX_SOCKET */
 
-bool grpc_parse_ipv4(const grpc_uri *uri,
-                     grpc_resolved_address *resolved_addr) {
-  if (strcmp("ipv4", uri->scheme) != 0) {
-    gpr_log(GPR_ERROR, "Expected 'ipv4' scheme, got '%s'", uri->scheme);
-    return false;
-  }
-  const char *host_port = uri->path;
+bool grpc_parse_ipv4_hostport(const char *hostport, grpc_resolved_address *addr,
+                              bool log_errors) {
+  bool success = false;
+  // Split host and port.
   char *host;
   char *port;
-  int port_num;
-  bool result = false;
-  struct sockaddr_in *in = (struct sockaddr_in *)resolved_addr->addr;
-
-  if (*host_port == '/') ++host_port;
-  if (!gpr_split_host_port(host_port, &host, &port)) {
-    return false;
-  }
-
-  memset(resolved_addr, 0, sizeof(grpc_resolved_address));
-  resolved_addr->len = sizeof(struct sockaddr_in);
+  if (!gpr_split_host_port(hostport, &host, &port)) return false;
+  // Parse IP address.
+  memset(addr, 0, sizeof(*addr));
+  addr->len = sizeof(struct sockaddr_in);
+  struct sockaddr_in *in = (struct sockaddr_in *)addr->addr;
   in->sin_family = AF_INET;
   if (inet_pton(AF_INET, host, &in->sin_addr) == 0) {
-    gpr_log(GPR_ERROR, "invalid ipv4 address: '%s'", host);
+    if (log_errors) gpr_log(GPR_ERROR, "invalid ipv4 address: '%s'", host);
     goto done;
   }
-
-  if (port != NULL) {
-    if (sscanf(port, "%d", &port_num) != 1 || port_num < 0 ||
-        port_num > 65535) {
-      gpr_log(GPR_ERROR, "invalid ipv4 port: '%s'", port);
-      goto done;
-    }
-    in->sin_port = htons((uint16_t)port_num);
-  } else {
-    gpr_log(GPR_ERROR, "no port given for ipv4 scheme");
+  // Parse port.
+  if (port == NULL) {
+    if (log_errors) gpr_log(GPR_ERROR, "no port given for ipv4 scheme");
     goto done;
   }
-
-  result = true;
+  int port_num;
+  if (sscanf(port, "%d", &port_num) != 1 || port_num < 0 || port_num > 65535) {
+    if (log_errors) gpr_log(GPR_ERROR, "invalid ipv4 port: '%s'", port);
+    goto done;
+  }
+  in->sin_port = htons((uint16_t)port_num);
+  success = true;
 done:
   gpr_free(host);
   gpr_free(port);
-  return result;
+  return success;
 }
 
-bool grpc_parse_ipv6(const grpc_uri *uri,
+bool grpc_parse_ipv4(const grpc_uri *uri,
                      grpc_resolved_address *resolved_addr) {
-  if (strcmp("ipv6", uri->scheme) != 0) {
-    gpr_log(GPR_ERROR, "Expected 'ipv6' scheme, got '%s'", uri->scheme);
+  if (strcmp("ipv4", uri->scheme) != 0) {
+    gpr_log(GPR_ERROR, "Expected 'ipv4' scheme, got '%s'", uri->scheme);
     return false;
   }
   const char *host_port = uri->path;
-  char *host;
-  char *port;
-  int port_num;
-  int result = 0;
-  struct sockaddr_in6 *in6 = (struct sockaddr_in6 *)resolved_addr->addr;
-
   if (*host_port == '/') ++host_port;
-  if (!gpr_split_host_port(host_port, &host, &port)) {
-    return 0;
-  }
+  return grpc_parse_ipv4_hostport(host_port, resolved_addr,
+                                  true /* log_errors */);
+}
 
-  memset(in6, 0, sizeof(*in6));
-  resolved_addr->len = sizeof(*in6);
+bool grpc_parse_ipv6_hostport(const char *hostport, grpc_resolved_address *addr,
+                              bool log_errors) {
+  bool success = false;
+  // Split host and port.
+  char *host;
+  char *port;
+  if (!gpr_split_host_port(hostport, &host, &port)) return false;
+  // Parse IP address.
+  memset(addr, 0, sizeof(*addr));
+  addr->len = sizeof(struct sockaddr_in6);
+  struct sockaddr_in6 *in6 = (struct sockaddr_in6 *)addr->addr;
   in6->sin6_family = AF_INET6;
-
-  /* Handle the RFC6874 syntax for IPv6 zone identifiers. */
+  // Handle the RFC6874 syntax for IPv6 zone identifiers.
   char *host_end = (char *)gpr_memrchr(host, '%', strlen(host));
   if (host_end != NULL) {
     GPR_ASSERT(host_end >= host);
@@ -159,7 +150,7 @@ bool grpc_parse_ipv6(const grpc_uri *uri,
       gpr_log(GPR_ERROR, "invalid ipv6 scope id: '%s'", host_end + 1);
       goto done;
     }
-    // Handle "sin6_scope_id" being type "u_long". See grpc issue ##10027.
+    // Handle "sin6_scope_id" being type "u_long". See grpc issue #10027.
     in6->sin6_scope_id = sin6_scope_id;
   } else {
     if (inet_pton(AF_INET6, host, &in6->sin6_addr) == 0) {
@@ -167,24 +158,34 @@ bool grpc_parse_ipv6(const grpc_uri *uri,
       goto done;
     }
   }
-
-  if (port != NULL) {
-    if (sscanf(port, "%d", &port_num) != 1 || port_num < 0 ||
-        port_num > 65535) {
-      gpr_log(GPR_ERROR, "invalid ipv6 port: '%s'", port);
-      goto done;
-    }
-    in6->sin6_port = htons((uint16_t)port_num);
-  } else {
-    gpr_log(GPR_ERROR, "no port given for ipv6 scheme");
+  // Parse port.
+  if (port == NULL) {
+    if (log_errors) gpr_log(GPR_ERROR, "no port given for ipv6 scheme");
     goto done;
   }
-
-  result = 1;
+  int port_num;
+  if (sscanf(port, "%d", &port_num) != 1 || port_num < 0 || port_num > 65535) {
+    if (log_errors) gpr_log(GPR_ERROR, "invalid ipv6 port: '%s'", port);
+    goto done;
+  }
+  in6->sin6_port = htons((uint16_t)port_num);
+  success = true;
 done:
   gpr_free(host);
   gpr_free(port);
-  return result;
+  return success;
+}
+
+bool grpc_parse_ipv6(const grpc_uri *uri,
+                     grpc_resolved_address *resolved_addr) {
+  if (strcmp("ipv6", uri->scheme) != 0) {
+    gpr_log(GPR_ERROR, "Expected 'ipv6' scheme, got '%s'", uri->scheme);
+    return false;
+  }
+  const char *host_port = uri->path;
+  if (*host_port == '/') ++host_port;
+  return grpc_parse_ipv6_hostport(host_port, resolved_addr,
+                                  true /* log_errors */);
 }
 
 bool grpc_parse_uri(const grpc_uri *uri, grpc_resolved_address *resolved_addr) {
diff --git a/src/core/ext/filters/client_channel/parse_address.h b/src/core/ext/filters/client_channel/parse_address.h
index fa7ea33a00..1a203a3b26 100644
--- a/src/core/ext/filters/client_channel/parse_address.h
+++ b/src/core/ext/filters/client_channel/parse_address.h
@@ -54,4 +54,10 @@ bool grpc_parse_ipv6(const grpc_uri *uri, grpc_resolved_address *resolved_addr);
 /** Populate \a resolved_addr from \a uri. Returns true upon success. */
 bool grpc_parse_uri(const grpc_uri *uri, grpc_resolved_address *resolved_addr);
 
+/** Parse bare IPv4 or IPv6 "IP:port" strings. */
+bool grpc_parse_ipv4_hostport(const char *hostport, grpc_resolved_address *addr,
+                              bool log_errors);
+bool grpc_parse_ipv6_hostport(const char *hostport, grpc_resolved_address *addr,
+                              bool log_errors);
+
 #endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_PARSE_ADDRESS_H */
diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.c b/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.c
index ffaeeed324..578e8d697f 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.c
+++ b/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.c
@@ -61,6 +61,8 @@
 typedef struct {
   /** base class: must be first */
   grpc_resolver base;
+  /** DNS server to use (if not system default) */
+  char *dns_server;
   /** name to resolve (usually the same as target_name) */
   char *name_to_resolve;
   /** default port to use */
@@ -172,6 +174,8 @@ static void dns_ares_on_resolved_locked(grpc_exec_ctx *exec_ctx, void *arg,
     grpc_resolved_addresses_destroy(r->addresses);
     grpc_lb_addresses_destroy(exec_ctx, addresses);
   } else {
+    const char *msg = grpc_error_string(error);
+    gpr_log(GPR_DEBUG, "dns resolution failed: %s", msg);
     gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
     gpr_timespec next_try = gpr_backoff_step(&r->backoff_state, now);
     gpr_timespec timeout = gpr_time_sub(next_try, now);
@@ -221,9 +225,9 @@ static void dns_ares_start_resolving_locked(grpc_exec_ctx *exec_ctx,
   GPR_ASSERT(!r->resolving);
   r->resolving = true;
   r->addresses = NULL;
-  grpc_resolve_address(exec_ctx, r->name_to_resolve, r->default_port,
-                       r->interested_parties, &r->dns_ares_on_resolved_locked,
-                       &r->addresses);
+  grpc_dns_lookup_ares(exec_ctx, r->dns_server, r->name_to_resolve,
+                       r->default_port, r->interested_parties,
+                       &r->dns_ares_on_resolved_locked, &r->addresses);
 }
 
 static void dns_ares_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
@@ -246,6 +250,7 @@ static void dns_ares_destroy(grpc_exec_ctx *exec_ctx, grpc_resolver *gr) {
     grpc_channel_args_destroy(exec_ctx, r->resolved_result);
   }
   grpc_pollset_set_destroy(exec_ctx, r->interested_parties);
+  gpr_free(r->dns_server);
   gpr_free(r->name_to_resolve);
   gpr_free(r->default_port);
   grpc_channel_args_destroy(exec_ctx, r->channel_args);
@@ -257,14 +262,13 @@ static grpc_resolver *dns_ares_create(grpc_exec_ctx *exec_ctx,
                                       const char *default_port) {
   // Get name from args.
   const char *path = args->uri->path;
-  if (0 != strcmp(args->uri->authority, "")) {
-    gpr_log(GPR_ERROR, "authority based dns uri's not supported");
-    return NULL;
-  }
   if (path[0] == '/') ++path;
   // Create resolver.
   ares_dns_resolver *r = gpr_zalloc(sizeof(ares_dns_resolver));
   grpc_resolver_init(&r->base, &dns_ares_resolver_vtable, args->combiner);
+  if (0 != strcmp(args->uri->authority, "")) {
+    r->dns_server = gpr_strdup(args->uri->authority);
+  }
   r->name_to_resolve = gpr_strdup(path);
   r->default_port = gpr_strdup(default_port);
   r->channel_args = grpc_channel_args_copy(args->args);
diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c b/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c
index 09c46a66e0..e0cfd8b629 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c
+++ b/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c
@@ -48,7 +48,10 @@
 #include <grpc/support/string_util.h>
 #include <grpc/support/time.h>
 #include <grpc/support/useful.h>
+
+#include "src/core/ext/filters/client_channel/parse_address.h"
 #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_ev_driver.h"
+#include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/iomgr/executor.h"
 #include "src/core/lib/iomgr/iomgr_internal.h"
 #include "src/core/lib/iomgr/sockaddr_utils.h"
@@ -58,6 +61,8 @@ static gpr_once g_basic_init = GPR_ONCE_INIT;
 static gpr_mu g_init_mu;
 
 typedef struct grpc_ares_request {
+  /** indicates the DNS server to use, if specified */
+  struct ares_addr_port_node dns_server_addr;
   /** following members are set in grpc_resolve_address_ares_impl */
   /** host to resolve, parsed from the name to resolve */
   char *host;
@@ -192,11 +197,12 @@ static void on_done_cb(void *arg, int status, int timeouts,
   grpc_ares_request_unref(NULL, r);
 }
 
-void grpc_resolve_address_ares_impl(grpc_exec_ctx *exec_ctx, const char *name,
-                                    const char *default_port,
-                                    grpc_pollset_set *interested_parties,
-                                    grpc_closure *on_done,
-                                    grpc_resolved_addresses **addrs) {
+void grpc_dns_lookup_ares(grpc_exec_ctx *exec_ctx, const char *dns_server,
+                          const char *name, const char *default_port,
+                          grpc_pollset_set *interested_parties,
+                          grpc_closure *on_done,
+                          grpc_resolved_addresses **addrs) {
+  grpc_error *error = GRPC_ERROR_NONE;
   /* TODO(zyc): Enable tracing after #9603 is checked in */
   /* if (grpc_dns_trace) {
       gpr_log(GPR_DEBUG, "resolve_address (blocking): name=%s, default_port=%s",
@@ -208,28 +214,23 @@ void grpc_resolve_address_ares_impl(grpc_exec_ctx *exec_ctx, const char *name,
   char *port;
   gpr_split_host_port(name, &host, &port);
   if (host == NULL) {
-    grpc_error *err = grpc_error_set_str(
+    error = grpc_error_set_str(
         GRPC_ERROR_CREATE_FROM_STATIC_STRING("unparseable host:port"),
         GRPC_ERROR_STR_TARGET_ADDRESS, grpc_slice_from_copied_string(name));
-    grpc_closure_sched(exec_ctx, on_done, err);
     goto error_cleanup;
   } else if (port == NULL) {
     if (default_port == NULL) {
-      grpc_error *err = grpc_error_set_str(
+      error = grpc_error_set_str(
           GRPC_ERROR_CREATE_FROM_STATIC_STRING("no port in name"),
           GRPC_ERROR_STR_TARGET_ADDRESS, grpc_slice_from_copied_string(name));
-      grpc_closure_sched(exec_ctx, on_done, err);
       goto error_cleanup;
     }
     port = gpr_strdup(default_port);
   }
 
   grpc_ares_ev_driver *ev_driver;
-  grpc_error *err = grpc_ares_ev_driver_create(&ev_driver, interested_parties);
-  if (err != GRPC_ERROR_NONE) {
-    GRPC_LOG_IF_ERROR("grpc_ares_ev_driver_create() failed", err);
-    goto error_cleanup;
-  }
+  error = grpc_ares_ev_driver_create(&ev_driver, interested_parties);
+  if (error != GRPC_ERROR_NONE) goto error_cleanup;
 
   grpc_ares_request *r = gpr_malloc(sizeof(grpc_ares_request));
   gpr_mu_init(&r->mu);
@@ -242,6 +243,40 @@ void grpc_resolve_address_ares_impl(grpc_exec_ctx *exec_ctx, const char *name,
   r->success = false;
   r->error = GRPC_ERROR_NONE;
   ares_channel *channel = grpc_ares_ev_driver_get_channel(r->ev_driver);
+
+  // If dns_server is specified, use it.
+  if (dns_server != NULL) {
+    gpr_log(GPR_INFO, "Using DNS server %s", dns_server);
+    grpc_resolved_address addr;
+    if (grpc_parse_ipv4_hostport(dns_server, &addr, false /* log_errors */)) {
+      r->dns_server_addr.family = AF_INET;
+      memcpy(&r->dns_server_addr.addr.addr4, addr.addr, addr.len);
+      r->dns_server_addr.tcp_port = grpc_sockaddr_get_port(&addr);
+      r->dns_server_addr.udp_port = grpc_sockaddr_get_port(&addr);
+    } else if (grpc_parse_ipv6_hostport(dns_server, &addr,
+                                        false /* log_errors */)) {
+      r->dns_server_addr.family = AF_INET6;
+      memcpy(&r->dns_server_addr.addr.addr6, addr.addr, addr.len);
+      r->dns_server_addr.tcp_port = grpc_sockaddr_get_port(&addr);
+      r->dns_server_addr.udp_port = grpc_sockaddr_get_port(&addr);
+    } else {
+      error = grpc_error_set_str(
+          GRPC_ERROR_CREATE_FROM_STATIC_STRING("cannot parse authority"),
+          GRPC_ERROR_STR_TARGET_ADDRESS, grpc_slice_from_copied_string(name));
+      goto error_cleanup;
+    }
+    int status = ares_set_servers_ports(*channel, &r->dns_server_addr);
+    if (status != ARES_SUCCESS) {
+      char *error_msg;
+      gpr_asprintf(&error_msg, "C-ares status is not ARES_SUCCESS: %s",
+                   ares_strerror(status));
+      error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
+      gpr_free(error_msg);
+      goto error_cleanup;
+    }
+  }
+  // An extra reference is put here to avoid destroying the request in
+  // on_done_cb before calling grpc_ares_ev_driver_start.
   gpr_ref_init(&r->pending_queries, 2);
   if (grpc_ipv6_loopback_available()) {
     gpr_ref(&r->pending_queries);
@@ -254,10 +289,20 @@ void grpc_resolve_address_ares_impl(grpc_exec_ctx *exec_ctx, const char *name,
   return;
 
 error_cleanup:
+  grpc_closure_sched(exec_ctx, on_done, error);
   gpr_free(host);
   gpr_free(port);
 }
 
+void grpc_resolve_address_ares_impl(grpc_exec_ctx *exec_ctx, const char *name,
+                                    const char *default_port,
+                                    grpc_pollset_set *interested_parties,
+                                    grpc_closure *on_done,
+                                    grpc_resolved_addresses **addrs) {
+  grpc_dns_lookup_ares(exec_ctx, NULL /* dns_server */, name, default_port,
+                       interested_parties, on_done, addrs);
+}
+
 void (*grpc_resolve_address_ares)(
     grpc_exec_ctx *exec_ctx, const char *name, const char *default_port,
     grpc_pollset_set *interested_parties, grpc_closure *on_done,
diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h b/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h
index 3dd40ea268..84fd7fcbd6 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h
+++ b/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h
@@ -51,6 +51,12 @@ extern void (*grpc_resolve_address_ares)(grpc_exec_ctx *exec_ctx,
                                          grpc_closure *on_done,
                                          grpc_resolved_addresses **addresses);
 
+void grpc_dns_lookup_ares(grpc_exec_ctx *exec_ctx, const char *dns_server,
+                          const char *addr, const char *default_port,
+                          grpc_pollset_set *interested_parties,
+                          grpc_closure *on_done,
+                          grpc_resolved_addresses **addresses);
+
 /* Initialize gRPC ares wrapper. Must be called at least once before
    grpc_resolve_address_ares(). */
 grpc_error *grpc_ares_init(void);
diff --git a/src/core/ext/filters/client_channel/subchannel.c b/src/core/ext/filters/client_channel/subchannel.c
index b2de85c4a1..dd14bf1d02 100644
--- a/src/core/ext/filters/client_channel/subchannel.c
+++ b/src/core/ext/filters/client_channel/subchannel.c
@@ -283,6 +283,7 @@ static void disconnect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
 void grpc_subchannel_unref(grpc_exec_ctx *exec_ctx,
                            grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   gpr_atm old_refs;
+  // add a weak ref and subtract a strong ref (atomically)
   old_refs = ref_mutate(c, (gpr_atm)1 - (gpr_atm)(1 << INTERNAL_REF_BITS),
                         1 REF_MUTATE_PURPOSE("STRONG_UNREF"));
   if ((old_refs & STRONG_REF_MASK) == (1 << INTERNAL_REF_BITS)) {
@@ -656,7 +657,6 @@ static bool publish_transport_locked(grpc_exec_ctx *exec_ctx,
     gpr_free(sw_subchannel);
     grpc_channel_stack_destroy(exec_ctx, stk);
     gpr_free(con);
-    GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "connecting");
     return false;
   }
 
@@ -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/client_channel/subchannel_index.c b/src/core/ext/filters/client_channel/subchannel_index.c
index f6ef4a845e..b25dbfcf51 100644
--- a/src/core/ext/filters/client_channel/subchannel_index.c
+++ b/src/core/ext/filters/client_channel/subchannel_index.c
@@ -183,8 +183,11 @@ grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
   enter_ctx(exec_ctx);
 
   grpc_subchannel *c = NULL;
+  bool need_to_unref_constructed;
 
   while (c == NULL) {
+    need_to_unref_constructed = false;
+
     // Compare and swap loop:
     // - take a reference to the current index
     gpr_mu_lock(&g_mu);
@@ -194,8 +197,11 @@ grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
     // - Check to see if a subchannel already exists
     c = gpr_avl_get(index, key);
     if (c != NULL) {
+      c = GRPC_SUBCHANNEL_REF_FROM_WEAK_REF(c, "index_register");
+    }
+    if (c != NULL) {
       // yes -> we're done
-      GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, constructed, "index_register");
+      need_to_unref_constructed = true;
     } else {
       // no -> update the avl and compare/swap
       gpr_avl updated =
@@ -219,6 +225,10 @@ grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
 
   leave_ctx(exec_ctx);
 
+  if (need_to_unref_constructed) {
+    GRPC_SUBCHANNEL_UNREF(exec_ctx, constructed, "index_register");
+  }
+
   return c;
 }
 
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/filters/workarounds/workaround_cronet_compression_filter.c b/src/core/ext/filters/workarounds/workaround_cronet_compression_filter.c
new file mode 100644
index 0000000000..7fb75e3a4f
--- /dev/null
+++ b/src/core/ext/filters/workarounds/workaround_cronet_compression_filter.c
@@ -0,0 +1,223 @@
+//
+// 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/workarounds/workaround_cronet_compression_filter.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+
+#include "src/core/ext/filters/workarounds/workaround_utils.h"
+#include "src/core/lib/channel/channel_stack_builder.h"
+#include "src/core/lib/surface/channel_init.h"
+#include "src/core/lib/transport/metadata.h"
+
+typedef struct call_data {
+  // Receive closures are chained: we inject this closure as the
+  // recv_initial_metadata_ready up-call on transport_stream_op, and remember to
+  // call our next_recv_initial_metadata_ready member after handling it.
+  grpc_closure recv_initial_metadata_ready;
+  // Used by recv_initial_metadata_ready.
+  grpc_metadata_batch* recv_initial_metadata;
+  // Original recv_initial_metadata_ready callback, invoked after our own.
+  grpc_closure* next_recv_initial_metadata_ready;
+
+  // Marks whether the workaround is active
+  bool workaround_active;
+} call_data;
+
+// Find the user agent metadata element in the batch
+static bool get_user_agent_mdelem(const grpc_metadata_batch* batch,
+                                  grpc_mdelem* md) {
+  if (batch->idx.named.user_agent != NULL) {
+    *md = batch->idx.named.user_agent->md;
+    return true;
+  }
+  return false;
+}
+
+// Callback invoked when we receive an initial metadata.
+static void recv_initial_metadata_ready(grpc_exec_ctx* exec_ctx,
+                                        void* user_data, grpc_error* error) {
+  grpc_call_element* elem = user_data;
+  call_data* calld = elem->call_data;
+
+  if (GRPC_ERROR_NONE == error) {
+    grpc_mdelem md;
+    if (get_user_agent_mdelem(calld->recv_initial_metadata, &md)) {
+      grpc_workaround_user_agent_md* user_agent_md = grpc_parse_user_agent(md);
+      if (user_agent_md
+              ->workaround_active[GRPC_WORKAROUND_ID_CRONET_COMPRESSION]) {
+        calld->workaround_active = true;
+      }
+    }
+  }
+
+  // Invoke the next callback.
+  grpc_closure_run(exec_ctx, calld->next_recv_initial_metadata_ready,
+                   GRPC_ERROR_REF(error));
+}
+
+// Start transport stream op.
+static void start_transport_stream_op_batch(
+    grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+    grpc_transport_stream_op_batch* op) {
+  call_data* calld = elem->call_data;
+
+  // Inject callback for receiving initial metadata
+  if (op->recv_initial_metadata) {
+    calld->next_recv_initial_metadata_ready =
+        op->payload->recv_initial_metadata.recv_initial_metadata_ready;
+    op->payload->recv_initial_metadata.recv_initial_metadata_ready =
+        &calld->recv_initial_metadata_ready;
+    calld->recv_initial_metadata =
+        op->payload->recv_initial_metadata.recv_initial_metadata;
+  }
+
+  if (op->send_message) {
+    /* Send message happens after client's user-agent (initial metadata) is
+     * received, so workaround_active must be set already */
+    if (calld->workaround_active) {
+      op->payload->send_message.send_message->flags |= GRPC_WRITE_NO_COMPRESS;
+    }
+  }
+
+  // Chain to the next filter.
+  grpc_call_next_op(exec_ctx, elem, op);
+}
+
+// Constructor for call_data.
+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;
+  calld->next_recv_initial_metadata_ready = NULL;
+  calld->workaround_active = false;
+  grpc_closure_init(&calld->recv_initial_metadata_ready,
+                    recv_initial_metadata_ready, elem,
+                    grpc_schedule_on_exec_ctx);
+  return GRPC_ERROR_NONE;
+}
+
+// Destructor for call_data.
+static void destroy_call_elem(grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+                              const grpc_call_final_info* final_info,
+                              grpc_closure* ignored) {}
+
+// Constructor for channel_data.
+static grpc_error* init_channel_elem(grpc_exec_ctx* exec_ctx,
+                                     grpc_channel_element* elem,
+                                     grpc_channel_element_args* args) {
+  return GRPC_ERROR_NONE;
+}
+
+// Destructor for channel_data.
+static void destroy_channel_elem(grpc_exec_ctx* exec_ctx,
+                                 grpc_channel_element* elem) {}
+
+// Parse the user agent
+static bool parse_user_agent(grpc_mdelem md) {
+  const char grpc_objc_specifier[] = "grpc-objc/";
+  const size_t grpc_objc_specifier_len = sizeof(grpc_objc_specifier) - 1;
+  const char cronet_specifier[] = "cronet_http";
+  const size_t cronet_specifier_len = sizeof(cronet_specifier) - 1;
+
+  char* user_agent_str = grpc_slice_to_c_string(GRPC_MDVALUE(md));
+  bool grpc_objc_specifier_seen = false;
+  bool cronet_specifier_seen = false;
+  char *major_version_str = user_agent_str, *minor_version_str;
+  long major_version, minor_version;
+
+  char* head = strtok(user_agent_str, " ");
+  while (head != NULL) {
+    if (!grpc_objc_specifier_seen &&
+        0 == strncmp(head, grpc_objc_specifier, grpc_objc_specifier_len)) {
+      major_version_str = head + grpc_objc_specifier_len;
+      grpc_objc_specifier_seen = true;
+    } else if (grpc_objc_specifier_seen &&
+               0 == strncmp(head, cronet_specifier, cronet_specifier_len)) {
+      cronet_specifier_seen = true;
+      break;
+    }
+
+    head = strtok(NULL, " ");
+  }
+  if (grpc_objc_specifier_seen) {
+    major_version_str = strtok(major_version_str, ".");
+    minor_version_str = strtok(NULL, ".");
+    major_version = atol(major_version_str);
+    minor_version = atol(minor_version_str);
+  }
+
+  gpr_free(user_agent_str);
+  return (grpc_objc_specifier_seen && cronet_specifier_seen &&
+          (major_version < 1 || (major_version == 1 && minor_version <= 3)));
+}
+
+const grpc_channel_filter grpc_workaround_cronet_compression_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,
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    grpc_channel_next_get_info,
+    "workaround_cronet_compression"};
+
+static bool register_workaround_cronet_compression(
+    grpc_exec_ctx* exec_ctx, grpc_channel_stack_builder* builder, void* arg) {
+  const grpc_channel_args* channel_args =
+      grpc_channel_stack_builder_get_channel_arguments(builder);
+  const grpc_arg* a = grpc_channel_args_find(
+      channel_args, GRPC_ARG_WORKAROUND_CRONET_COMPRESSION);
+  if (a == NULL) {
+    return true;
+  }
+  if (grpc_channel_arg_get_bool(a, false) == false) {
+    return true;
+  }
+  return grpc_channel_stack_builder_prepend_filter(
+      builder, &grpc_workaround_cronet_compression_filter, NULL, NULL);
+}
+
+void grpc_workaround_cronet_compression_filter_init(void) {
+  grpc_channel_init_register_stage(
+      GRPC_SERVER_CHANNEL, GRPC_WORKAROUND_PRIORITY_HIGH,
+      register_workaround_cronet_compression, NULL);
+  grpc_register_workaround(GRPC_WORKAROUND_ID_CRONET_COMPRESSION,
+                           parse_user_agent);
+}
+
+void grpc_workaround_cronet_compression_filter_shutdown(void) {}
diff --git a/src/core/ext/filters/workarounds/workaround_cronet_compression_filter.h b/src/core/ext/filters/workarounds/workaround_cronet_compression_filter.h
new file mode 100644
index 0000000000..58c79a0c00
--- /dev/null
+++ b/src/core/ext/filters/workarounds/workaround_cronet_compression_filter.h
@@ -0,0 +1,40 @@
+//
+// 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_WORKAROUNDS_WORKAROUND_CRONET_COMPRESSION_FILTER_H
+#define GRPC_CORE_EXT_FILTERS_WORKAROUNDS_WORKAROUND_CRONET_COMPRESSION_FILTER_H
+
+#include "src/core/lib/channel/channel_stack.h"
+
+extern const grpc_channel_filter grpc_workaround_cronet_compression_filter;
+
+#endif /* GRPC_CORE_EXT_FILTERS_WORKAROUNDS_WORKAROUND_CRONET_COMPRESSION_FILTER_H \
+        */
diff --git a/src/core/ext/filters/workarounds/workaround_utils.c b/src/core/ext/filters/workarounds/workaround_utils.c
new file mode 100644
index 0000000000..1c565388e1
--- /dev/null
+++ b/src/core/ext/filters/workarounds/workaround_utils.c
@@ -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.
+//
+
+#include "src/core/ext/filters/workarounds/workaround_utils.h"
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+user_agent_parser ua_parser[GRPC_MAX_WORKAROUND_ID];
+
+static void destroy_user_agent_md(void *user_agent_md) {
+  gpr_free(user_agent_md);
+}
+
+grpc_workaround_user_agent_md *grpc_parse_user_agent(grpc_mdelem md) {
+  grpc_workaround_user_agent_md *user_agent_md =
+      (grpc_workaround_user_agent_md *)grpc_mdelem_get_user_data(
+          md, destroy_user_agent_md);
+
+  if (NULL != user_agent_md) {
+    return user_agent_md;
+  }
+  user_agent_md = gpr_malloc(sizeof(grpc_workaround_user_agent_md));
+  for (int i = 0; i < GRPC_MAX_WORKAROUND_ID; i++) {
+    if (ua_parser[i]) {
+      user_agent_md->workaround_active[i] = ua_parser[i](md);
+    }
+  }
+  grpc_mdelem_set_user_data(md, destroy_user_agent_md, (void *)user_agent_md);
+
+  return user_agent_md;
+}
+
+void grpc_register_workaround(uint32_t id, user_agent_parser parser) {
+  GPR_ASSERT(id < GRPC_MAX_WORKAROUND_ID);
+  ua_parser[id] = parser;
+}
diff --git a/src/core/ext/filters/workarounds/workaround_utils.h b/src/core/ext/filters/workarounds/workaround_utils.h
new file mode 100644
index 0000000000..7cd70c12d8
--- /dev/null
+++ b/src/core/ext/filters/workarounds/workaround_utils.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_EXT_FILTERS_WORKAROUNDS_WORKAROUND_UTILS_H
+#define GRPC_CORE_EXT_FILTERS_WORKAROUNDS_WORKAROUND_UTILS_H
+
+#include <grpc/support/workaround_list.h>
+
+#include "src/core/lib/transport/metadata.h"
+
+#define GRPC_WORKAROUND_PRIORITY_HIGH 10001
+#define GRPC_WORKAROUND_PROIRITY_LOW 9999
+
+typedef struct grpc_workaround_user_agent_md {
+  bool workaround_active[GRPC_MAX_WORKAROUND_ID];
+} grpc_workaround_user_agent_md;
+
+grpc_workaround_user_agent_md *grpc_parse_user_agent(grpc_mdelem md);
+
+typedef bool (*user_agent_parser)(grpc_mdelem);
+
+void grpc_register_workaround(uint32_t id, user_agent_parser parser);
+
+#endif
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..f3268bcfca 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 +2139,41 @@ 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;
-  } else {
-    bdp = (uint32_t)(bdp_dbl);
-  }
+  // initial window size bounded [1,2^31-1], but we set the min to 128.
+  int32_t bdp = GPR_CLAMP((int32_t)bdp_dbl, 128, INT32_MAX);
   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);
+}
+
+static void update_frame(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
+                         double bw_dbl, double bdp_dbl) {
+  int32_t bdp = GPR_CLAMP((int32_t)bdp_dbl, 128, INT32_MAX);
+  int32_t target = GPR_MAX((int32_t)bw_dbl / 1000, bdp);
+  // frame size is bounded [2^14,2^24-1]
+  int32_t frame_size = GPR_CLAMP(target, 16384, 16777215);
+  int64_t delta = (int64_t)frame_size -
+                  (int64_t)t->settings[GRPC_LOCAL_SETTINGS]
+                                      [GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE];
+  if (delta == 0 || (delta > -frame_size / 10 && delta < frame_size / 10)) {
+    return;
+  }
+  if (GRPC_TRACER_ON(grpc_bdp_estimator_trace)) {
+    gpr_log(GPR_DEBUG, "%s: update max_frame size to %d", t->peer_string,
+            (int)frame_size);
+  }
+  push_setting(exec_ctx, t, GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE,
+               (uint32_t)frame_size);
 }
 
 static grpc_error *try_http_parsing(grpc_exec_ctx *exec_ctx,
@@ -2269,6 +2292,7 @@ static void read_action_locked(grpc_exec_ctx *exec_ctx, void *tp,
       }
 
       int64_t estimate = -1;
+      double bdp_guess = -1;
       if (grpc_bdp_estimator_get_estimate(&t->bdp_estimator, &estimate)) {
         double target = 1 + log2((double)estimate);
         double memory_pressure = grpc_resource_quota_get_memory_pressure(
@@ -2286,9 +2310,15 @@ static void read_action_locked(grpc_exec_ctx *exec_ctx, void *tp,
         }
         double log2_bdp_guess =
             grpc_pid_controller_update(&t->pid_controller, bdp_error, dt);
-        update_bdp(exec_ctx, t, pow(2, log2_bdp_guess));
+        bdp_guess = pow(2, log2_bdp_guess);
+        update_bdp(exec_ctx, t, bdp_guess);
         t->last_pid_update = now;
       }
+
+      double bw = -1;
+      if (grpc_bdp_estimator_get_bw(&t->bdp_estimator, &bw)) {
+        update_frame(exec_ctx, t, bw, bdp_guess);
+      }
     }
     GRPC_CHTTP2_UNREF_TRANSPORT(exec_ctx, t, "keep_reading");
   } else {
@@ -2305,7 +2335,7 @@ 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 +2348,7 @@ 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 +2809,7 @@ 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 +2817,8 @@ 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 +2839,7 @@ 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]) {