Merge pull request #16225 from markdroth/reset_connection_backoff

Reset connection backoff

21 files changed, 191 insertions, 1 deletions

diff --git a/grpc.def b/grpc.def
index 5b98792662..5e9d86c769 100644
--- a/grpc.def
+++ b/grpc.def
@@ -42,6 +42,7 @@ EXPORTS
     grpc_census_call_get_context
     grpc_channel_get_target
     grpc_channel_get_info
+    grpc_channel_reset_connect_backoff
     grpc_insecure_channel_create
     grpc_lame_client_channel_create
     grpc_channel_destroy
diff --git a/include/grpc/grpc.h b/include/grpc/grpc.h
index 3245aa5580..348c7a316f 100644
--- a/include/grpc/grpc.h
+++ b/include/grpc/grpc.h
@@ -274,6 +274,11 @@ GRPCAPI char* grpc_channel_get_target(grpc_channel* channel);
 GRPCAPI void grpc_channel_get_info(grpc_channel* channel,
                                    const grpc_channel_info* channel_info);
 
+/** EXPERIMENTAL.  Resets the channel's connect backoff.
+    TODO(roth): When we see whether this proves useful, either promote
+    to non-experimental or remove it. */
+GRPCAPI void grpc_channel_reset_connect_backoff(grpc_channel* channel);
+
 /** Create a client channel to 'target'. Additional channel level configuration
     MAY be provided by grpc_channel_args, though the expectation is that most
     clients will want to simply pass NULL. The user data in 'args' need only
diff --git a/include/grpcpp/channel.h b/include/grpcpp/channel.h
index 4b45d5382c..fed02bf7bc 100644
--- a/include/grpcpp/channel.h
+++ b/include/grpcpp/channel.h
@@ -30,6 +30,14 @@
 struct grpc_channel;
 
 namespace grpc {
+
+namespace experimental {
+/// Resets the channel's connection backoff.
+/// TODO(roth): Once we see whether this proves useful, either create a gRFC
+/// and change this to be a method of the Channel class, or remove it.
+void ChannelResetConnectionBackoff(Channel* channel);
+}  // namespace experimental
+
 /// Channels represent a connection to an endpoint. Created by \a CreateChannel.
 class Channel final : public ChannelInterface,
                       public internal::CallHook,
@@ -52,6 +60,7 @@ class Channel final : public ChannelInterface,
  private:
   template <class InputMessage, class OutputMessage>
   friend class internal::BlockingUnaryCallImpl;
+  friend void experimental::ChannelResetConnectionBackoff(Channel* channel);
   friend std::shared_ptr<Channel> CreateChannelInternal(
       const grpc::string& host, grpc_channel* c_channel);
   Channel(const grpc::string& host, grpc_channel* c_channel);
diff --git a/src/core/ext/filters/client_channel/client_channel.cc b/src/core/ext/filters/client_channel/client_channel.cc
index fead8feb17..b06f09d8c7 100644
--- a/src/core/ext/filters/client_channel/client_channel.cc
+++ b/src/core/ext/filters/client_channel/client_channel.cc
@@ -622,6 +622,17 @@ static void start_transport_op_locked(void* arg, grpc_error* error_ignored) {
     }
     GRPC_ERROR_UNREF(op->disconnect_with_error);
   }
+
+  if (op->reset_connect_backoff) {
+    if (chand->resolver != nullptr) {
+      chand->resolver->ResetBackoffLocked();
+      chand->resolver->RequestReresolutionLocked();
+    }
+    if (chand->lb_policy != nullptr) {
+      chand->lb_policy->ResetBackoffLocked();
+    }
+  }
+
   GRPC_CHANNEL_STACK_UNREF(chand->owning_stack, "start_transport_op");
 
   GRPC_CLOSURE_SCHED(op->on_consumed, GRPC_ERROR_NONE);
diff --git a/src/core/ext/filters/client_channel/lb_policy.h b/src/core/ext/filters/client_channel/lb_policy.h
index 31c08246ae..3c0a9c1118 100644
--- a/src/core/ext/filters/client_channel/lb_policy.h
+++ b/src/core/ext/filters/client_channel/lb_policy.h
@@ -144,7 +144,10 @@ class LoadBalancingPolicy
   /// consider whether this method is still needed.
   virtual void ExitIdleLocked() GRPC_ABSTRACT;
 
-  /// populates child_subchannels and child_channels with the uuids of this
+  /// Resets connection backoff.
+  virtual void ResetBackoffLocked() GRPC_ABSTRACT;
+
+  /// Populates child_subchannels and child_channels with the uuids of this
   /// LB policy's referenced children. This is not invoked from the
   /// client_channel's combiner. The implementation is responsible for
   /// providing its own synchronization.
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
index af6f3fe296..6581385ff9 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
@@ -134,6 +134,7 @@ class GrpcLb : public LoadBalancingPolicy {
       grpc_error** connectivity_error) override;
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void ExitIdleLocked() override;
+  void ResetBackoffLocked() override;
   void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
                                 ChildRefsList* child_channels) override;
 
@@ -1214,6 +1215,15 @@ void GrpcLb::ExitIdleLocked() {
   }
 }
 
+void GrpcLb::ResetBackoffLocked() {
+  if (lb_channel_ != nullptr) {
+    grpc_channel_reset_connect_backoff(lb_channel_);
+  }
+  if (rr_policy_ != nullptr) {
+    rr_policy_->ResetBackoffLocked();
+  }
+}
+
 bool GrpcLb::PickLocked(PickState* pick, grpc_error** error) {
   PendingPick* pp = PendingPickCreate(pick);
   bool pick_done = false;
diff --git a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
index 46acbf628b..2b6a9ba8c5 100644
--- a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
@@ -57,6 +57,7 @@ class PickFirst : public LoadBalancingPolicy {
       grpc_error** connectivity_error) override;
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void ExitIdleLocked() override;
+  void ResetBackoffLocked() override;
   void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
                                 ChildRefsList* ignored) override;
 
@@ -259,6 +260,13 @@ void PickFirst::ExitIdleLocked() {
   }
 }
 
+void PickFirst::ResetBackoffLocked() {
+  subchannel_list_->ResetBackoffLocked();
+  if (latest_pending_subchannel_list_ != nullptr) {
+    latest_pending_subchannel_list_->ResetBackoffLocked();
+  }
+}
+
 bool PickFirst::PickLocked(PickState* pick, grpc_error** error) {
   // If we have a selected subchannel already, return synchronously.
   if (selected_ != nullptr) {
diff --git a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
index 9c3a15c67b..fea84331d8 100644
--- a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
@@ -68,6 +68,7 @@ class RoundRobin : public LoadBalancingPolicy {
       grpc_error** connectivity_error) override;
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void ExitIdleLocked() override;
+  void ResetBackoffLocked() override;
   void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
                                 ChildRefsList* ignored) override;
 
@@ -333,6 +334,13 @@ void RoundRobin::ExitIdleLocked() {
   }
 }
 
+void RoundRobin::ResetBackoffLocked() {
+  subchannel_list_->ResetBackoffLocked();
+  if (latest_pending_subchannel_list_ != nullptr) {
+    latest_pending_subchannel_list_->ResetBackoffLocked();
+  }
+}
+
 bool RoundRobin::DoPickLocked(PickState* pick) {
   const size_t next_ready_index =
       subchannel_list_->GetNextReadySubchannelIndexLocked();
diff --git a/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h b/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
index 018ac3bb86..0fa2f04e73 100644
--- a/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
+++ b/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
@@ -107,6 +107,11 @@ class SubchannelData {
   // being unreffed.
   virtual void UnrefSubchannelLocked(const char* reason);
 
+  // Resets the connection backoff.
+  // TODO(roth): This method should go away when we move the backoff
+  // code out of the subchannel and into the LB policies.
+  void ResetBackoffLocked();
+
   // Starts watching the connectivity state of the subchannel.
   // ProcessConnectivityChangeLocked() will be called when the
   // connectivity state changes.
@@ -206,6 +211,11 @@ class SubchannelList
   LoadBalancingPolicy* policy() const { return policy_; }
   TraceFlag* tracer() const { return tracer_; }
 
+  // Resets connection backoff of all subchannels.
+  // TODO(roth): We will probably need to rethink this as part of moving
+  // the backoff code out of subchannels and into LB policies.
+  void ResetBackoffLocked();
+
   // Note: Caller must ensure that this is invoked inside of the combiner.
   void Orphan() override {
     ShutdownLocked();
@@ -300,6 +310,14 @@ void SubchannelData<SubchannelListType, SubchannelDataType>::
 
 template <typename SubchannelListType, typename SubchannelDataType>
 void SubchannelData<SubchannelListType,
+                    SubchannelDataType>::ResetBackoffLocked() {
+  if (subchannel_ != nullptr) {
+    grpc_subchannel_reset_backoff(subchannel_);
+  }
+}
+
+template <typename SubchannelListType, typename SubchannelDataType>
+void SubchannelData<SubchannelListType,
                     SubchannelDataType>::StartConnectivityWatchLocked() {
   if (subchannel_list_->tracer()->enabled()) {
     gpr_log(GPR_INFO,
@@ -544,6 +562,15 @@ void SubchannelList<SubchannelListType, SubchannelDataType>::ShutdownLocked() {
   }
 }
 
+template <typename SubchannelListType, typename SubchannelDataType>
+void SubchannelList<SubchannelListType,
+                    SubchannelDataType>::ResetBackoffLocked() {
+  for (size_t i = 0; i < subchannels_.size(); i++) {
+    SubchannelDataType* sd = &subchannels_[i];
+    sd->ResetBackoffLocked();
+  }
+}
+
 }  // namespace grpc_core
 
 #endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_SUBCHANNEL_LIST_H */
diff --git a/src/core/ext/filters/client_channel/resolver.h b/src/core/ext/filters/client_channel/resolver.h
index c7e37e4468..48f2e89095 100644
--- a/src/core/ext/filters/client_channel/resolver.h
+++ b/src/core/ext/filters/client_channel/resolver.h
@@ -94,6 +94,14 @@ class Resolver : public InternallyRefCountedWithTracing<Resolver> {
   /// throw away unselected subchannels.
   virtual void RequestReresolutionLocked() GRPC_ABSTRACT;
 
+  /// Resets the re-resolution backoff, if any.
+  /// This needs to be implemented only by pull-based implementations;
+  /// for push-based implementations, it will be a no-op.
+  /// TODO(roth): Pull the backoff code out of resolver and into
+  /// client_channel, so that it can be shared across resolver
+  /// implementations.  At that point, this method can go away.
+  virtual void ResetBackoffLocked() {}
+
   void Orphan() override {
     // Invoke ShutdownAndUnrefLocked() inside of the combiner.
     GRPC_CLOSURE_SCHED(
diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc b/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
index 7050e82121..f2bb5f3c71 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
+++ b/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
@@ -66,6 +66,8 @@ class AresDnsResolver : public Resolver {
 
   void RequestReresolutionLocked() override;
 
+  void ResetBackoffLocked() override;
+
   void ShutdownLocked() override;
 
  private:
@@ -187,6 +189,13 @@ void AresDnsResolver::RequestReresolutionLocked() {
   }
 }
 
+void AresDnsResolver::ResetBackoffLocked() {
+  if (have_next_resolution_timer_) {
+    grpc_timer_cancel(&next_resolution_timer_);
+  }
+  backoff_.Reset();
+}
+
 void AresDnsResolver::ShutdownLocked() {
   if (have_next_resolution_timer_) {
     grpc_timer_cancel(&next_resolution_timer_);
diff --git a/src/core/ext/filters/client_channel/resolver/dns/native/dns_resolver.cc b/src/core/ext/filters/client_channel/resolver/dns/native/dns_resolver.cc
index fae4c33a17..282caf215c 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/native/dns_resolver.cc
+++ b/src/core/ext/filters/client_channel/resolver/dns/native/dns_resolver.cc
@@ -58,6 +58,8 @@ class NativeDnsResolver : public Resolver {
 
   void RequestReresolutionLocked() override;
 
+  void ResetBackoffLocked() override;
+
   void ShutdownLocked() override;
 
  private:
@@ -158,6 +160,13 @@ void NativeDnsResolver::RequestReresolutionLocked() {
   }
 }
 
+void NativeDnsResolver::ResetBackoffLocked() {
+  if (have_next_resolution_timer_) {
+    grpc_timer_cancel(&next_resolution_timer_);
+  }
+  backoff_.Reset();
+}
+
 void NativeDnsResolver::ShutdownLocked() {
   if (have_next_resolution_timer_) {
     grpc_timer_cancel(&next_resolution_timer_);
diff --git a/src/core/ext/filters/client_channel/subchannel.cc b/src/core/ext/filters/client_channel/subchannel.cc
index 71ef8c518b..48c6030c89 100644
--- a/src/core/ext/filters/client_channel/subchannel.cc
+++ b/src/core/ext/filters/client_channel/subchannel.cc
@@ -132,6 +132,8 @@ struct grpc_subchannel {
   bool have_alarm;
   /** have we started the backoff loop */
   bool backoff_begun;
+  // reset_backoff() was called while alarm was pending
+  bool deferred_reset_backoff;
   /** our alarm */
   grpc_timer alarm;
 
@@ -438,6 +440,9 @@ static void on_alarm(void* arg, grpc_error* error) {
   if (c->disconnected) {
     error = GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING("Disconnected",
                                                              &error, 1);
+  } else if (c->deferred_reset_backoff) {
+    c->deferred_reset_backoff = false;
+    error = GRPC_ERROR_NONE;
   } else {
     GRPC_ERROR_REF(error);
   }
@@ -675,6 +680,19 @@ static void on_subchannel_connected(void* arg, grpc_error* error) {
   grpc_channel_args_destroy(delete_channel_args);
 }
 
+void grpc_subchannel_reset_backoff(grpc_subchannel* subchannel) {
+  gpr_mu_lock(&subchannel->mu);
+  if (subchannel->have_alarm) {
+    subchannel->deferred_reset_backoff = true;
+    grpc_timer_cancel(&subchannel->alarm);
+  } else {
+    subchannel->backoff_begun = false;
+    subchannel->backoff->Reset();
+    maybe_start_connecting_locked(subchannel);
+  }
+  gpr_mu_unlock(&subchannel->mu);
+}
+
 /*
  * grpc_subchannel_call implementation
  */
diff --git a/src/core/ext/filters/client_channel/subchannel.h b/src/core/ext/filters/client_channel/subchannel.h
index 9e53f7d542..a135035d62 100644
--- a/src/core/ext/filters/client_channel/subchannel.h
+++ b/src/core/ext/filters/client_channel/subchannel.h
@@ -145,6 +145,13 @@ grpc_subchannel_get_connected_subchannel(grpc_subchannel* c);
 const grpc_subchannel_key* grpc_subchannel_get_key(
     const grpc_subchannel* subchannel);
 
+// Resets the connection backoff of the subchannel.
+// TODO(roth): Move connection backoff out of subchannels and up into LB
+// policy code (probably by adding a SubchannelGroup between
+// SubchannelList and SubchannelData), at which point this method can
+// go away.
+void grpc_subchannel_reset_backoff(grpc_subchannel* subchannel);
+
 /** continue processing a transport op */
 void grpc_subchannel_call_process_op(grpc_subchannel_call* subchannel_call,
                                      grpc_transport_stream_op_batch* op);
diff --git a/src/core/lib/surface/channel.cc b/src/core/lib/surface/channel.cc
index 7cbd61adef..82635d3c21 100644
--- a/src/core/lib/surface/channel.cc
+++ b/src/core/lib/surface/channel.cc
@@ -281,6 +281,17 @@ void grpc_channel_get_info(grpc_channel* channel,
   elem->filter->get_channel_info(elem, channel_info);
 }
 
+void grpc_channel_reset_connect_backoff(grpc_channel* channel) {
+  grpc_core::ExecCtx exec_ctx;
+  GRPC_API_TRACE("grpc_channel_reset_connect_backoff(channel=%p)", 1,
+                 (channel));
+  grpc_transport_op* op = grpc_make_transport_op(nullptr);
+  op->reset_connect_backoff = true;
+  grpc_channel_element* elem =
+      grpc_channel_stack_element(CHANNEL_STACK_FROM_CHANNEL(channel), 0);
+  elem->filter->start_transport_op(elem, op);
+}
+
 static grpc_call* grpc_channel_create_call_internal(
     grpc_channel* channel, grpc_call* parent_call, uint32_t propagation_mask,
     grpc_completion_queue* cq, grpc_pollset_set* pollset_set_alternative,
diff --git a/src/core/lib/transport/transport.h b/src/core/lib/transport/transport.h
index 585b9dfae9..9e784635c6 100644
--- a/src/core/lib/transport/transport.h
+++ b/src/core/lib/transport/transport.h
@@ -282,6 +282,8 @@ typedef struct grpc_transport_op {
     /** Called when the ping ack is received */
     grpc_closure* on_ack;
   } send_ping;
+  // If true, will reset the channel's connection backoff.
+  bool reset_connect_backoff;
 
   /***************************************************************************
    * remaining fields are initialized and used at the discretion of the
diff --git a/src/cpp/client/channel_cc.cc b/src/cpp/client/channel_cc.cc
index 867f31f025..39b891c2e1 100644
--- a/src/cpp/client/channel_cc.cc
+++ b/src/cpp/client/channel_cc.cc
@@ -84,6 +84,14 @@ grpc::string Channel::GetServiceConfigJSON() const {
                              &channel_info.service_config_json);
 }
 
+namespace experimental {
+
+void ChannelResetConnectionBackoff(Channel* channel) {
+  grpc_channel_reset_connect_backoff(channel->c_channel_);
+}
+
+}  // namespace experimental
+
 internal::Call Channel::CreateCall(const internal::RpcMethod& method,
                                    ClientContext* context,
                                    CompletionQueue* cq) {
diff --git a/src/ruby/ext/grpc/rb_grpc_imports.generated.c b/src/ruby/ext/grpc/rb_grpc_imports.generated.c
index 2443532bb8..38b68462df 100644
--- a/src/ruby/ext/grpc/rb_grpc_imports.generated.c
+++ b/src/ruby/ext/grpc/rb_grpc_imports.generated.c
@@ -65,6 +65,7 @@ grpc_census_call_set_context_type grpc_census_call_set_context_import;
 grpc_census_call_get_context_type grpc_census_call_get_context_import;
 grpc_channel_get_target_type grpc_channel_get_target_import;
 grpc_channel_get_info_type grpc_channel_get_info_import;
+grpc_channel_reset_connect_backoff_type grpc_channel_reset_connect_backoff_import;
 grpc_insecure_channel_create_type grpc_insecure_channel_create_import;
 grpc_lame_client_channel_create_type grpc_lame_client_channel_create_import;
 grpc_channel_destroy_type grpc_channel_destroy_import;
@@ -315,6 +316,7 @@ void grpc_rb_load_imports(HMODULE library) {
   grpc_census_call_get_context_import = (grpc_census_call_get_context_type) GetProcAddress(library, "grpc_census_call_get_context");
   grpc_channel_get_target_import = (grpc_channel_get_target_type) GetProcAddress(library, "grpc_channel_get_target");
   grpc_channel_get_info_import = (grpc_channel_get_info_type) GetProcAddress(library, "grpc_channel_get_info");
+  grpc_channel_reset_connect_backoff_import = (grpc_channel_reset_connect_backoff_type) GetProcAddress(library, "grpc_channel_reset_connect_backoff");
   grpc_insecure_channel_create_import = (grpc_insecure_channel_create_type) GetProcAddress(library, "grpc_insecure_channel_create");
   grpc_lame_client_channel_create_import = (grpc_lame_client_channel_create_type) GetProcAddress(library, "grpc_lame_client_channel_create");
   grpc_channel_destroy_import = (grpc_channel_destroy_type) GetProcAddress(library, "grpc_channel_destroy");
diff --git a/src/ruby/ext/grpc/rb_grpc_imports.generated.h b/src/ruby/ext/grpc/rb_grpc_imports.generated.h
index b08a1f94f7..d6add00d12 100644
--- a/src/ruby/ext/grpc/rb_grpc_imports.generated.h
+++ b/src/ruby/ext/grpc/rb_grpc_imports.generated.h
@@ -170,6 +170,9 @@ extern grpc_channel_get_target_type grpc_channel_get_target_import;
 typedef void(*grpc_channel_get_info_type)(grpc_channel* channel, const grpc_channel_info* channel_info);
 extern grpc_channel_get_info_type grpc_channel_get_info_import;
 #define grpc_channel_get_info grpc_channel_get_info_import
+typedef void(*grpc_channel_reset_connect_backoff_type)(grpc_channel* channel);
+extern grpc_channel_reset_connect_backoff_type grpc_channel_reset_connect_backoff_import;
+#define grpc_channel_reset_connect_backoff grpc_channel_reset_connect_backoff_import
 typedef grpc_channel*(*grpc_insecure_channel_create_type)(const char* target, const grpc_channel_args* args, void* reserved);
 extern grpc_insecure_channel_create_type grpc_insecure_channel_create_import;
 #define grpc_insecure_channel_create grpc_insecure_channel_create_import
diff --git a/test/core/surface/public_headers_must_be_c89.c b/test/core/surface/public_headers_must_be_c89.c
index 9f4ad2b4d7..7b3e875cf0 100644
--- a/test/core/surface/public_headers_must_be_c89.c
+++ b/test/core/surface/public_headers_must_be_c89.c
@@ -104,6 +104,7 @@ int main(int argc, char **argv) {
   printf("%lx", (unsigned long) grpc_census_call_get_context);
   printf("%lx", (unsigned long) grpc_channel_get_target);
   printf("%lx", (unsigned long) grpc_channel_get_info);
+  printf("%lx", (unsigned long) grpc_channel_reset_connect_backoff);
   printf("%lx", (unsigned long) grpc_insecure_channel_create);
   printf("%lx", (unsigned long) grpc_lame_client_channel_create);
   printf("%lx", (unsigned long) grpc_channel_destroy);
diff --git a/test/cpp/end2end/client_lb_end2end_test.cc b/test/cpp/end2end/client_lb_end2end_test.cc
index c5a73a2469..7fe0da8aae 100644
--- a/test/cpp/end2end/client_lb_end2end_test.cc
+++ b/test/cpp/end2end/client_lb_end2end_test.cc
@@ -408,6 +408,36 @@ TEST_F(ClientLbEnd2endTest, PickFirstBackOffMinReconnect) {
   gpr_atm_rel_store(&g_connection_delay_ms, 0);
 }
 
+TEST_F(ClientLbEnd2endTest, PickFirstResetConnectionBackoff) {
+  ChannelArguments args;
+  constexpr int kInitialBackOffMs = 1000;
+  args.SetInt(GRPC_ARG_INITIAL_RECONNECT_BACKOFF_MS, kInitialBackOffMs);
+  const std::vector<int> ports = {grpc_pick_unused_port_or_die()};
+  auto channel = BuildChannel("pick_first", args);
+  auto stub = BuildStub(channel);
+  SetNextResolution(ports);
+  // The channel won't become connected (there's no server).
+  EXPECT_FALSE(
+      channel->WaitForConnected(grpc_timeout_milliseconds_to_deadline(10)));
+  // Bring up a server on the chosen port.
+  StartServers(1, ports);
+  const gpr_timespec t0 = gpr_now(GPR_CLOCK_MONOTONIC);
+  // Wait for connect, but not long enough.  This proves that we're
+  // being throttled by initial backoff.
+  EXPECT_FALSE(
+      channel->WaitForConnected(grpc_timeout_milliseconds_to_deadline(10)));
+  // Reset connection backoff.
+  experimental::ChannelResetConnectionBackoff(channel.get());
+  // Wait for connect.  Should happen ~immediately.
+  EXPECT_TRUE(
+      channel->WaitForConnected(grpc_timeout_milliseconds_to_deadline(10)));
+  const gpr_timespec t1 = gpr_now(GPR_CLOCK_MONOTONIC);
+  const grpc_millis waited_ms = gpr_time_to_millis(gpr_time_sub(t1, t0));
+  gpr_log(GPR_DEBUG, "Waited %" PRId64 " milliseconds", waited_ms);
+  // We should have waited less than kInitialBackOffMs.
+  EXPECT_LT(waited_ms, kInitialBackOffMs);
+}
+
 TEST_F(ClientLbEnd2endTest, PickFirstUpdates) {
   // Start servers and send one RPC per server.
   const int kNumServers = 3;