Limit QUIC's Cubic CWND increases to 1/2 the bytes acked when in

net/quic/core/congestion_control/cubic.cc

Index: net/quic/core/congestion_control/cubic.cc
diff --git a/net/quic/core/congestion_control/cubic.cc b/net/quic/core/congestion_control/cubic.cc
index fc596c973f924fa567dcf1d2f77fc033db0beb9e..89a347e7e8edd6edf05fcd0f08a17bd459e84148 100644
--- a/net/quic/core/congestion_control/cubic.cc
+++ b/net/quic/core/congestion_control/cubic.cc
@@ -14,6 +14,7 @@
 #include "net/quic/core/quic_time.h"
 
 using std::max;
+using std::min;
 
 namespace net {
 
@@ -74,6 +75,7 @@ void Cubic::Reset() {
   last_congestion_window_ = 0;
   last_max_congestion_window_ = 0;
   acked_packets_count_ = 0;
+  epoch_packets_count_ = 0;
   estimated_tcp_congestion_window_ = 0;
   origin_point_congestion_window_ = 0;
   time_to_origin_point_ = 0;
@@ -104,6 +106,7 @@ QuicPacketCount Cubic::CongestionWindowAfterAck(
     QuicPacketCount current_congestion_window,
     QuicTime::Delta delay_min) {
   acked_packets_count_ += 1;  // Packets acked.
+  epoch_packets_count_ += 1;
   QuicTime current_time = clock_->ApproximateNow();
 
   // Cubic is "independent" of RTT, the update is limited by the time elapsed.
@@ -119,6 +122,7 @@ QuicPacketCount Cubic::CongestionWindowAfterAck(
     // First ACK after a loss event.
     epoch_ = current_time;     // Start of epoch.
     acked_packets_count_ = 1;  // Reset count.
+    epoch_packets_count_ = 1;
     // Reset estimated_tcp_congestion_window_ to be in sync with cubic.
     estimated_tcp_congestion_window_ = current_congestion_window;
     if (last_max_congestion_window_ <= current_congestion_window) {
@@ -146,6 +150,14 @@ QuicPacketCount Cubic::CongestionWindowAfterAck(
   QuicPacketCount target_congestion_window =
       origin_point_congestion_window_ - delta_congestion_window;
 
+  if (FLAGS_quic_limit_cubic_cwnd_increase) {
+    // Limit the CWND increase to half the acked packets rounded up to the
+    // nearest packet.
+    target_congestion_window =
+        min(target_congestion_window,
+            current_congestion_window + (epoch_packets_count_ + 1) / 2);
+  }
+
   DCHECK_LT(0u, estimated_tcp_congestion_window_);
   // With dynamic beta/alpha based on number of active streams, it is possible
   // for the required_ack_count to become much lower than acked_packets_count_
@@ -160,6 +172,7 @@ QuicPacketCount Cubic::CongestionWindowAfterAck(
     acked_packets_count_ -= required_ack_count;
     estimated_tcp_congestion_window_++;
   }
+  epoch_packets_count_ = 0;
 
   // We have a new cubic congestion window.
   last_target_congestion_window_ = target_congestion_window;