Repair the CWND reduction caused by spurious RTO's in QUIC's congestion

net/quic/congestion_control/rtt_stats_test.cc

 // Copyright 2014 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/rtt_stats.h"
 
 #include "base/logging.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
@@ skipping 136 matching lines @@
   // A new all time low sets both the min_rtt and the recent_min_rtt.
   rtt_sample = QuicTime::Delta::FromMilliseconds(5);
   rtt_stats_.UpdateRtt(rtt_sample, QuicTime::Delta::Zero(), now);
 
   EXPECT_EQ(rtt_sample, rtt_stats_.min_rtt());
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetQuarterWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample, RttStatsPeer::GetHalfWindowRtt(&rtt_stats_));
   EXPECT_EQ(rtt_sample, rtt_stats_.recent_min_rtt());
 }
 
+TEST_F(RttStatsTest, ExpireSmoothedMetrics) {
+  QuicTime::Delta initial_rtt = QuicTime::Delta::FromMilliseconds(10);
+  rtt_stats_.UpdateRtt(initial_rtt, QuicTime::Delta::Zero(), QuicTime::Zero());
+  EXPECT_EQ(initial_rtt, rtt_stats_.min_rtt());
+  EXPECT_EQ(initial_rtt, rtt_stats_.recent_min_rtt());
+  EXPECT_EQ(initial_rtt, rtt_stats_.SmoothedRtt());
 
+  EXPECT_EQ(initial_rtt.Multiply(0.5), rtt_stats_.mean_deviation());
+
+  // Update once with a 20ms RTT.
+  QuicTime::Delta doubled_rtt = initial_rtt.Multiply(2);
+  rtt_stats_.UpdateRtt(doubled_rtt, QuicTime::Delta::Zero(), QuicTime::Zero());
+  EXPECT_EQ(initial_rtt.Multiply(1.125), rtt_stats_.SmoothedRtt());
+
+  // Expire the smoothed metrics, increasing smoothed rtt and mean deviation.
+  rtt_stats_.ExpireSmoothedMetrics();
+  EXPECT_EQ(doubled_rtt, rtt_stats_.SmoothedRtt());
+  EXPECT_EQ(initial_rtt.Multiply(0.875), rtt_stats_.mean_deviation());
+}
 
 }  // namespace test
 }  // namespace net