From c7de81e57ec4131993bd469a146739d74d564ab1 Mon Sep 17 00:00:00 2001
From: Vijay Pai <vpai@google.com>
Date: Fri, 5 Jun 2015 03:32:03 -0700
Subject: [PATCH] Better management of channel attempts and channel coverage

---
 test/cpp/qps/client_async.cc | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/test/cpp/qps/client_async.cc b/test/cpp/qps/client_async.cc
index dc62d1152fa..24d8b3751d4 100644
--- a/test/cpp/qps/client_async.cc
+++ b/test/cpp/qps/client_async.cc
@@ -154,7 +154,8 @@ class AsyncClient : public Client {
       Client(config), channel_lock_(config.client_channels()),
       contexts_(config.client_channels()),
       max_outstanding_per_channel_(config.outstanding_rpcs_per_channel()),
-      channel_count_(config.client_channels()) {
+      channel_count_(config.client_channels()),
+      pref_channel_inc_(config.async_client_threads()) {
 
     SetupLoadTest(config, config.async_client_threads());
 
@@ -265,17 +266,17 @@ class AsyncClient : public Client {
        grpc_time_source::now() >= next_issue_[thread_idx]) {
      // Attempt to issue
      bool issued = false;
-     for (int num_attempts = 0; num_attempts < channel_count_ && !issued;
-	  num_attempts++) {
+     for (int num_attempts = 0, channel_attempt = next_channel_[thread_idx];
+          num_attempts < channel_count_ && !issued; num_attempts++) {
        bool can_issue = false;
        ClientRpcContext* ctx = nullptr;
        {
          std::lock_guard<std::mutex>
-             g(channel_lock_[next_channel_[thread_idx]]);
-         if (!contexts_[next_channel_[thread_idx]].empty()) {
+             g(channel_lock_[channel_attempt]);
+         if (!contexts_[channel_attempt].empty()) {
            // Get an idle context from the front of the list
-           ctx = *(contexts_[next_channel_[thread_idx]].begin());
-           contexts_[next_channel_[thread_idx]].pop_front();
+           ctx = *(contexts_[channel_attempt].begin());
+           contexts_[channel_attempt].pop_front();
            can_issue = true;
          }
        }
@@ -288,10 +289,14 @@ class AsyncClient : public Client {
          ctx->set_deadline_posn(it);
          ctx->Start(cli_cqs_[thread_idx].get());
 	 issued = true;
+         // If we did issue, then next time, try our thread's next
+         // preferred channel
+         next_channel_[thread_idx] += pref_channel_inc_;
+         if (next_channel_[thread_idx] >= channel_count_)
+           next_channel_[thread_idx] = (thread_idx % channel_count_);
        } else {
-         // Do a modular increment of next_channel only if we didn't issue
-         next_channel_[thread_idx] =
-             (next_channel_[thread_idx]+1)%channel_count_;
+         // Do a modular increment of channel attempt if we couldn't issue
+         channel_attempt = (channel_attempt+1) % channel_count_;
        }
      }
      if (issued) {
@@ -319,6 +324,7 @@ class AsyncClient : public Client {
   std::vector<context_list> contexts_; // per-channel list of idle contexts
   int max_outstanding_per_channel_;
   int channel_count_;
+  int pref_channel_inc_;
 };
 
 class AsyncUnaryClient GRPC_FINAL : public AsyncClient {