Land Recent QUIC Changes

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"
 
+#include <complex>  // std::abs
+
 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);
@@ skipping 16 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_));
+  mean_deviation_ =
+      max(mean_deviation_,
+          QuicTime::Delta::FromMicroseconds(
+              std::abs(smoothed_rtt_.Subtract(latest_rtt_).ToMicroseconds())));

[wtc, 2014/07/23 23:31:42]

Why do we need to convert to microseconds and then convert back? So we can take
the absolute value?

[ramant (doing other things), 2014/07/23 23:56:47]

Seems like that.

Ian Swett: wdyt?

   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);
@@ skipping 73 matching lines @@
 }
 
 QuicTime::Delta RttStats::SmoothedRtt() const {
   if (!HasUpdates()) {
     return QuicTime::Delta::FromMicroseconds(initial_rtt_us_);
   }
   return smoothed_rtt_;
 }
 
 }  // namespace net