Update from https://crrev.com/303153

net/quic/congestion_control/tcp_cubic_sender.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/tcp_cubic_sender.h"
 
 #include <algorithm>
 
 #include "base/metrics/histogram.h"
 #include "net/quic/congestion_control/prr_sender.h"
 #include "net/quic/congestion_control/rtt_stats.h"
 #include "net/quic/crypto/crypto_protocol.h"
 
 using std::max;
 using std::min;
 
 namespace net {
 
 namespace {
 // Constants based on TCP defaults.
 // The minimum cwnd based on RFC 3782 (TCP NewReno) for cwnd reductions on a
 // fast retransmission.  The cwnd after a timeout is still 1.
 const QuicPacketCount kMinimumCongestionWindow = 2;
 const QuicByteCount kMaxSegmentSize = kDefaultTCPMSS;
-const int64 kInitialCongestionWindow = 10;
 const int kMaxBurstLength = 3;
 const float kRenoBeta = 0.7f;  // Reno backoff factor.
 const uint32 kDefaultNumConnections = 2;  // N-connection emulation.
 }  // namespace
 
 TcpCubicSender::TcpCubicSender(
     const QuicClock* clock,
     const RttStats* rtt_stats,
     bool reno,
     QuicPacketCount max_tcp_congestion_window,
     QuicConnectionStats* stats)
     : hybrid_slow_start_(clock),
       cubic_(clock, stats),
       rtt_stats_(rtt_stats),
       stats_(stats),
       reno_(reno),
       num_connections_(kDefaultNumConnections),
       congestion_window_count_(0),
       largest_sent_sequence_number_(0),
       largest_acked_sequence_number_(0),
       largest_sent_at_last_cutback_(0),
-      congestion_window_(kInitialCongestionWindow),
+      congestion_window_(kDefaultInitialWindow),
       previous_congestion_window_(0),
       slowstart_threshold_(max_tcp_congestion_window),
       previous_slowstart_threshold_(0),
       last_cutback_exited_slowstart_(false),
       max_tcp_congestion_window_(max_tcp_congestion_window) {
 }
 
 TcpCubicSender::~TcpCubicSender() {
   UMA_HISTOGRAM_COUNTS("Net.QuicSession.FinalTcpCwnd", congestion_window_);
 }
 
 void TcpCubicSender::SetFromConfig(const QuicConfig& config, bool is_server) {
   if (is_server) {
     if (config.HasReceivedConnectionOptions() &&
         ContainsQuicTag(config.ReceivedConnectionOptions(), kIW10)) {
       // Initial window experiment.  Ignore the initial congestion
       // window suggested by the client and use the default ICWND of
       // 10 instead.
-      congestion_window_ = kInitialCongestionWindow;
+      congestion_window_ = kDefaultInitialWindow;
     } else if (config.HasReceivedInitialCongestionWindow()) {
       // Set the initial window size.
-      congestion_window_ = min(kMaxInitialWindow,
-                               config.ReceivedInitialCongestionWindow());
+      congestion_window_ = max(kMinimumCongestionWindow,
+          min(kMaxInitialWindow,
+              static_cast<QuicPacketCount>(
+                  config.ReceivedInitialCongestionWindow())));
     }
   }
 }
 
 void TcpCubicSender::SetNumEmulatedConnections(int num_connections) {
   num_connections_ = max(1, num_connections);
   cubic_.SetNumConnections(num_connections_);
 }
 
 float TcpCubicSender::RenoBeta() const {
   // kNConnectionBeta is the backoff factor after loss for our N-connection
   // emulation, which emulates the effective backoff of an ensemble of N
   // TCP-Reno connections on a single loss event. The effective multiplier is
   // computed as:
   return (num_connections_ - 1 + kRenoBeta) / num_connections_;
 }
 
 void TcpCubicSender::OnCongestionEvent(
     bool rtt_updated,
     QuicByteCount bytes_in_flight,
     const CongestionVector& acked_packets,
     const CongestionVector& lost_packets) {
   if (rtt_updated && InSlowStart() &&
       hybrid_slow_start_.ShouldExitSlowStart(rtt_stats_->latest_rtt(),
-                                             rtt_stats_->MinRtt(),
+                                             rtt_stats_->min_rtt(),
                                              congestion_window_)) {
     slowstart_threshold_ = congestion_window_;
   }
   for (CongestionVector::const_iterator it = lost_packets.begin();
        it != lost_packets.end(); ++it) {
     OnPacketLost(it->first, bytes_in_flight);
   }
   for (CongestionVector::const_iterator it = acked_packets.begin();
        it != acked_packets.end(); ++it) {
     OnPacketAcked(it->first, it->second.bytes_sent, bytes_in_flight);
@@ skipping 90 matching lines @@
   if (GetCongestionWindow() > bytes_in_flight) {
     return QuicTime::Delta::Zero();
   }
   return QuicTime::Delta::Infinite();
 }
 
 QuicBandwidth TcpCubicSender::PacingRate() const {
   // We pace at twice the rate of the underlying sender's bandwidth estimate
   // during slow start and 1.25x during congestion avoidance to ensure pacing
   // doesn't prevent us from filling the window.
-  return BandwidthEstimate().Scale(InSlowStart() ? 2 : 1.25);
+  QuicTime::Delta srtt = rtt_stats_->smoothed_rtt();
+  if (srtt.IsZero()) {
+    srtt = QuicTime::Delta::FromMicroseconds(rtt_stats_->initial_rtt_us());
+  }
+  const QuicBandwidth bandwidth =
+      QuicBandwidth::FromBytesAndTimeDelta(GetCongestionWindow(), srtt);
+  return bandwidth.Scale(InSlowStart() ? 2 : 1.25);
 }
 
 QuicBandwidth TcpCubicSender::BandwidthEstimate() const {
-  if (rtt_stats_->SmoothedRtt().IsZero()) {
-    LOG(DFATAL) << "In BandwidthEstimate(), smoothed RTT is zero!";
+  QuicTime::Delta srtt = rtt_stats_->smoothed_rtt();
+  if (srtt.IsZero()) {
+    // If we haven't measured an rtt, the bandwidth estimate is unknown.
     return QuicBandwidth::Zero();
   }
-  return QuicBandwidth::FromBytesAndTimeDelta(GetCongestionWindow(),
-                                              rtt_stats_->SmoothedRtt());
+  return QuicBandwidth::FromBytesAndTimeDelta(GetCongestionWindow(), srtt);
 }
 
 bool TcpCubicSender::HasReliableBandwidthEstimate() const {
-  return !InSlowStart() && !InRecovery();
+  return !InSlowStart() && !InRecovery() &&
+      !rtt_stats_->smoothed_rtt().IsZero();;
 }
 
 QuicTime::Delta TcpCubicSender::RetransmissionDelay() const {
-  if (!rtt_stats_->HasUpdates()) {
+  if (rtt_stats_->smoothed_rtt().IsZero()) {
     return QuicTime::Delta::Zero();
   }
-  return rtt_stats_->SmoothedRtt().Add(
+  return rtt_stats_->smoothed_rtt().Add(
       rtt_stats_->mean_deviation().Multiply(4));
 }
 
 QuicByteCount TcpCubicSender::GetCongestionWindow() const {
   return congestion_window_ * kMaxSegmentSize;
 }
 
 bool TcpCubicSender::InSlowStart() const {
   return congestion_window_ < slowstart_threshold_;
 }
@@ skipping 55 matching lines @@
       ++congestion_window_;
       congestion_window_count_ = 0;
     }
 
     DVLOG(1) << "Reno; congestion window: " << congestion_window_
              << " slowstart threshold: " << slowstart_threshold_
              << " congestion window count: " << congestion_window_count_;
   } else {
     congestion_window_ = min(max_tcp_congestion_window_,
                              cubic_.CongestionWindowAfterAck(
-                                 congestion_window_, rtt_stats_->MinRtt()));
+                                 congestion_window_, rtt_stats_->min_rtt()));
     DVLOG(1) << "Cubic; congestion window: " << congestion_window_
              << " slowstart threshold: " << slowstart_threshold_;
   }
 }
 
 void TcpCubicSender::OnRetransmissionTimeout(bool packets_retransmitted) {
   largest_sent_at_last_cutback_ = 0;
   if (!packets_retransmitted) {
     return;
   }
@@ skipping 13 matching lines @@
   congestion_window_ = previous_congestion_window_;
   slowstart_threshold_ = previous_slowstart_threshold_;
   previous_congestion_window_ = 0;
 }
 
 CongestionControlType TcpCubicSender::GetCongestionControlType() const {
   return reno_ ? kReno : kCubic;
 }
 
 }  // namespace net