Use byte conservation instead of packet conservation in QUIC's Slow Start Large Recovery experiment…

net/quic/congestion_control/tcp_cubic_sender_packets.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_packets.h"
 
 #include <algorithm>
 
 #include "base/metrics/histogram_macros.h"
 #include "net/quic/congestion_control/prr_sender.h"
@@ skipping 62 matching lines @@
 void TcpCubicSenderPackets::SetMaxCongestionWindow(
     QuicByteCount max_congestion_window) {
   max_tcp_congestion_window_ = max_congestion_window / kDefaultTCPMSS;
 }
 
 void TcpCubicSenderPackets::ExitSlowstart() {
   slowstart_threshold_ = congestion_window_;
 }
 
 void TcpCubicSenderPackets::OnPacketLost(QuicPacketNumber packet_number,
+                                         QuicByteCount lost_bytes,
                                          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 1 for every loss.
-        congestion_window_ =
-            max(congestion_window_ - 1, min_congestion_window_);
+        if (FLAGS_quic_sslr_byte_conservation) {
+          if (stats_->slowstart_packets_lost == 1 ||
+              (stats_->slowstart_bytes_lost / kDefaultTCPMSS) >
+                  (stats_->slowstart_bytes_lost - lost_bytes) /
+                      kDefaultTCPMSS) {
+            // Reduce congestion window by 1 for every mss of bytes lost.
+            congestion_window_ =
+                max(congestion_window_ - 1, min_congestion_window_);
+          }
+        } else {
+          // Reduce congestion window by 1 for every loss.
+          congestion_window_ =
+              max(congestion_window_ - 1, min_congestion_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()) {
@@ skipping 92 matching lines @@
   congestion_window_ = initial_tcp_congestion_window_;
   slowstart_threshold_ = initial_max_tcp_congestion_window_;
   max_tcp_congestion_window_ = initial_max_tcp_congestion_window_;
 }
 
 CongestionControlType TcpCubicSenderPackets::GetCongestionControlType() const {
   return reno_ ? kReno : kCubic;
 }
 
 }  // namespace net