Removes QUIC flag and code that shifts cubic epoch on quiescence, since it's buggy and should not b…

net/quic/core/congestion_control/cubic.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/core/congestion_control/cubic.h"
 
 #include <stdint.h>
 #include <algorithm>
 #include <cmath>
 
@@ skipping 63 matching lines @@
   last_congestion_window_ = 0;
   last_max_congestion_window_ = 0;
   acked_packets_count_ = 0;
   estimated_tcp_congestion_window_ = 0;
   origin_point_congestion_window_ = 0;
   time_to_origin_point_ = 0;
   last_target_congestion_window_ = 0;
 }
 
 void Cubic::OnApplicationLimited() {
-  if (FLAGS_shift_quic_cubic_epoch_when_app_limited) {
-    // When sender is not using the available congestion window, Cubic's epoch
-    // should not continue growing. Record the time when sender goes into an
-    // app-limited period here, to compensate later when cwnd growth happens.
-    if (app_limited_start_time_ == QuicTime::Zero()) {
-      app_limited_start_time_ = clock_->ApproximateNow();
-    }
-  } else {
-    // When sender is not using the available congestion window, Cubic's epoch
-    // should not continue growing. Reset the epoch when in such a period.
-    epoch_ = QuicTime::Zero();
-  }
+  // When sender is not using the available congestion window, Cubic's epoch
+  // should not continue growing. Reset the epoch when in such a period.
+  epoch_ = QuicTime::Zero();
 }
 
 QuicPacketCount Cubic::CongestionWindowAfterPacketLoss(
     QuicPacketCount current_congestion_window) {
   if (current_congestion_window < last_max_congestion_window_) {
     // We never reached the old max, so assume we are competing with another
     // flow. Use our extra back off factor to allow the other flow to go up.
     last_max_congestion_window_ =
         static_cast<int>(kBetaLastMax * current_congestion_window);
   } else {
@@ skipping 26 matching lines @@
     estimated_tcp_congestion_window_ = current_congestion_window;
     if (last_max_congestion_window_ <= current_congestion_window) {
       time_to_origin_point_ = 0;
       origin_point_congestion_window_ = current_congestion_window;
     } else {
       time_to_origin_point_ = static_cast<uint32_t>(
           cbrt(kCubeFactor *
                (last_max_congestion_window_ - current_congestion_window)));
       origin_point_congestion_window_ = last_max_congestion_window_;
     }
-  } else {
-    // If sender was app-limited, then freeze congestion window growth during
-    // app-limited period. Continue growth now by shifting the epoch-start
-    // through the app-limited period.
-    if (FLAGS_shift_quic_cubic_epoch_when_app_limited &&
-        app_limited_start_time_ != QuicTime::Zero()) {
-      QuicTime::Delta shift = current_time - app_limited_start_time_;
-      DVLOG(1) << "Shifting epoch for quiescence by " << shift.ToMicroseconds();
-      epoch_ = epoch_ + shift;
-      app_limited_start_time_ = QuicTime::Zero();
-    }
   }
 
   // Change the time unit from microseconds to 2^10 fractions per second. Take
   // the round trip time in account. This is done to allow us to use shift as a
   // divide operator.
   int64_t elapsed_time =
       ((current_time + delay_min - epoch_).ToMicroseconds() << 10) /
       kNumMicrosPerSecond;
 
   int64_t offset = time_to_origin_point_ - elapsed_time;
@@ skipping 25 matching lines @@
   // congestion_window, use highest (fastest).
   if (target_congestion_window < estimated_tcp_congestion_window_) {
     target_congestion_window = estimated_tcp_congestion_window_;
   }
 
   DVLOG(1) << "Final target congestion_window: " << target_congestion_window;
   return target_congestion_window;
 }
 
 }  // namespace net