Landing Recent QUIC changes until 4/22/2016 14:55 UTC

net/quic/congestion_control/tcp_cubic_sender_bytes.cc

 // Copyright (c) 2015 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_bytes.h"
 
 #include <algorithm>
 
 #include "net/quic/congestion_control/prr_sender.h"
 #include "net/quic/congestion_control/rtt_stats.h"
@@ skipping 24 matching lines @@
     : TcpCubicSenderBase(clock, rtt_stats, reno, stats),
       cubic_(clock),
       num_acked_packets_(0),
       congestion_window_(initial_tcp_congestion_window * kDefaultTCPMSS),
       min_congestion_window_(kDefaultMinimumCongestionWindow),
       max_congestion_window_(max_congestion_window * kDefaultTCPMSS),
       slowstart_threshold_(max_congestion_window * kDefaultTCPMSS),
       initial_tcp_congestion_window_(initial_tcp_congestion_window *
                                      kDefaultTCPMSS),
       initial_max_tcp_congestion_window_(max_congestion_window *
-                                         kDefaultTCPMSS) {}
+                                         kDefaultTCPMSS),
+      min_slow_start_exit_window_(min_congestion_window_) {}
 
 TcpCubicSenderBytes::~TcpCubicSenderBytes() {}
 
 void TcpCubicSenderBytes::SetCongestionWindowFromBandwidthAndRtt(
     QuicBandwidth bandwidth,
     QuicTime::Delta rtt) {
-  // Make sure CWND is in appropriate range (in case of bad data).
   QuicByteCount new_congestion_window = bandwidth.ToBytesPerPeriod(rtt);
-  congestion_window_ =
-      max(min(new_congestion_window, kMaxCongestionWindow * kDefaultTCPMSS),
-          kMinCongestionWindowForBandwidthResumption * kDefaultTCPMSS);
+  if (FLAGS_quic_no_lower_bw_resumption_limit) {
+    // Limit new CWND if needed.
+    congestion_window_ =
+        max(min_congestion_window_,
+            min(new_congestion_window, kMaxCongestionWindow * kDefaultTCPMSS));
+  } else {
+    congestion_window_ =
+        max(min(new_congestion_window, kMaxCongestionWindow * kDefaultTCPMSS),
+            kMinCongestionWindowForBandwidthResumption * kDefaultTCPMSS);
+  }
 }
 
 void TcpCubicSenderBytes::SetCongestionWindowInPackets(
     QuicPacketCount congestion_window) {
   congestion_window_ = congestion_window * kDefaultTCPMSS;
 }
 
 void TcpCubicSenderBytes::SetMinCongestionWindowInPackets(
     QuicPacketCount congestion_window) {
   min_congestion_window_ = congestion_window * kDefaultTCPMSS;
@@ skipping 18 matching lines @@
                                        QuicByteCount bytes_in_flight) {
   // TCP NewReno (RFC6582) says that once a loss occurs, any losses in packets
   // already sent should be treated as a single loss event, since it's expected.
   if (packet_number <= largest_sent_at_last_cutback_) {
     if (last_cutback_exited_slowstart_) {
       ++stats_->slowstart_packets_lost;
       stats_->slowstart_bytes_lost += lost_bytes;
       if (slow_start_large_reduction_) {
         // Reduce congestion window by lost_bytes for every loss.
         congestion_window_ =
-            max(congestion_window_ - lost_bytes, min_congestion_window_);
+            max(congestion_window_ - lost_bytes, min_slow_start_exit_window_);
         slowstart_threshold_ = congestion_window_;
       }
     }
     DVLOG(1) << "Ignoring loss for largest_missing:" << packet_number
              << " because it was sent prior to the last CWND cutback.";
     return;
   }
   ++stats_->tcp_loss_events;
   last_cutback_exited_slowstart_ = InSlowStart();
   if (InSlowStart()) {
     ++stats_->slowstart_packets_lost;
   }
 
   prr_.OnPacketLost(bytes_in_flight);
 
   // TODO(jri): Separate out all of slow start into a separate class.
   if (slow_start_large_reduction_ && InSlowStart()) {
     DCHECK_LT(kDefaultTCPMSS, congestion_window_);
+    if (FLAGS_quic_sslr_limit_reduction &&
+        congestion_window_ >= 2 * initial_tcp_congestion_window_) {
+      min_slow_start_exit_window_ = congestion_window_ / 2;
+    }
     congestion_window_ = congestion_window_ - kDefaultTCPMSS;
   } else if (reno_) {
     congestion_window_ = congestion_window_ * RenoBeta();
   } else {
     congestion_window_ =
         cubic_.CongestionWindowAfterPacketLoss(congestion_window_);
   }
-  // Enforce TCP's minimum congestion window of 2*MSS.
   if (congestion_window_ < min_congestion_window_) {
     congestion_window_ = min_congestion_window_;
   }
   slowstart_threshold_ = congestion_window_;
   largest_sent_at_last_cutback_ = largest_sent_packet_number_;
   // Reset packet count from congestion avoidance mode. We start counting again
   // when we're out of recovery.
   num_acked_packets_ = 0;
   DVLOG(1) << "Incoming loss; congestion window: " << congestion_window_
            << " slowstart threshold: " << slowstart_threshold_;
@@ skipping 68 matching lines @@
   congestion_window_ = initial_tcp_congestion_window_;
   max_congestion_window_ = initial_max_tcp_congestion_window_;
   slowstart_threshold_ = initial_max_tcp_congestion_window_;
 }
 
 CongestionControlType TcpCubicSenderBytes::GetCongestionControlType() const {
   return reno_ ? kRenoBytes : kCubicBytes;
 }
 
 }  // namespace net