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

net/quic/congestion_control/rtt_stats.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"
 
+using std::max;
+
 namespace net {
 
 namespace {
 
 // Default initial rtt used before any samples are received.
 const int kInitialRttMs = 100;
 const float kAlpha = 0.125f;
 const float kOneMinusAlpha = (1 - kAlpha);
 const float kBeta = 0.25f;
 const float kOneMinusBeta = (1 - kBeta);
@@ skipping 13 matching lines @@
 
 bool RttStats::HasUpdates() const {
   return !smoothed_rtt_.IsZero();
 }
 
 void RttStats::SampleNewRecentMinRtt(uint32 num_samples) {
   num_min_rtt_samples_remaining_ = num_samples;
   new_min_rtt_ = RttSample();
 }
 
+void RttStats::ExpireSmoothedMetrics() {
+  mean_deviation_ = max(mean_deviation_, latest_rtt_.Subtract(smoothed_rtt_));
+  smoothed_rtt_ = max(smoothed_rtt_, latest_rtt_);
+}
+
 // Updates the RTT based on a new sample.
 void RttStats::UpdateRtt(QuicTime::Delta send_delta,
                          QuicTime::Delta ack_delay,
                          QuicTime now) {
   QuicTime::Delta rtt_sample(QuicTime::Delta::Zero());
   if (send_delta > ack_delay) {
     rtt_sample = send_delta.Subtract(ack_delay);
   } else if (!HasUpdates()) {
     // Even though we received information from the peer suggesting
     // an invalid (negative) RTT, we can use the send delta as an
@@ skipping 70 matching lines @@
 }
 
 QuicTime::Delta RttStats::SmoothedRtt() const {
   if (!HasUpdates()) {
     return QuicTime::Delta::FromMicroseconds(initial_rtt_us_);
   }
   return smoothed_rtt_;
 }
 
 }  // namespace net