Adds a varz variable to track the fraction of times we end up in cubic

net/quic/congestion_control/cubic.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/congestion_control/cubic.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
@@ skipping 55 matching lines @@
   acked_packets_count_ = 0;
   estimated_tcp_congestion_window_ = 0;
   origin_point_congestion_window_ = 0;
   time_to_origin_point_ = 0;
   last_target_congestion_window_ = 0;
 }
 
 void Cubic::UpdateCongestionControlStats(
     QuicTcpCongestionWindow new_cubic_mode_cwnd,
     QuicTcpCongestionWindow new_reno_mode_cwnd) {
-  if (last_congestion_window_ < new_cubic_mode_cwnd) {
-    // Congestion window will increase in cubic mode.
-    stats_->cwnd_increase_cubic_mode += new_cubic_mode_cwnd -
-        last_congestion_window_;
-    if (new_cubic_mode_cwnd <= new_reno_mode_cwnd) {
-      // Congestion window increase in reno mode is higher or equal to cubic
-      // mode's increase.
-      stats_->cwnd_increase_reno_mode += new_reno_mode_cwnd -
-          last_congestion_window_;
+
+  QuicTcpCongestionWindow highest_new_cwnd = std::max(new_cubic_mode_cwnd,
+                                                      new_reno_mode_cwnd);
+  if (last_congestion_window_ < highest_new_cwnd) {
+    // cwnd will increase to highest_new_cwnd.
+    stats_->cwnd_increase_congestion_avoidance +=
+        highest_new_cwnd - last_congestion_window_;
+    if (new_cubic_mode_cwnd > new_reno_mode_cwnd) {
+      // This cwnd increase is due to cubic mode.
+      stats_->cwnd_increase_cubic_mode +=
+          new_cubic_mode_cwnd - last_congestion_window_;
     }
-  } else if (last_congestion_window_ < new_reno_mode_cwnd) {
-    // No cwnd increase in cubic mode, but cwnd will increase in reno mode.
-    stats_->cwnd_increase_reno_mode += new_reno_mode_cwnd -
-        last_congestion_window_;
   }
 }
 
 QuicTcpCongestionWindow Cubic::CongestionWindowAfterPacketLoss(
     QuicTcpCongestionWindow current_congestion_window) {
   if (current_congestion_window < last_max_congestion_window_) {
     // We never reached the old max, so assume we are competing with another
     // flow. Use our extra back off factor to allow the other flow to go up.
     last_max_congestion_window_ =
         static_cast<int>(kBetaLastMax * current_congestion_window);
@@ skipping 76 matching lines @@
   // congestion_window, use highest (fastest).
   if (target_congestion_window < estimated_tcp_congestion_window_) {
     target_congestion_window = estimated_tcp_congestion_window_;
   }
 
   DVLOG(1) << "Target congestion_window: " << target_congestion_window;
   return target_congestion_window;
 }
 
 }  // namespace net