Don't let PRR kick in if there is less than a packets worth of bytes in

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/rtt_stats.h"
@@ skipping 314 matching lines @@
 
 void TcpCubicSender::PrrOnPacketAcked(QuicByteCount acked_bytes) {
   prr_delivered_ += acked_bytes;
   ++ack_count_since_loss_;
 }
 
 QuicTime::Delta TcpCubicSender::PrrTimeUntilSend(
     QuicByteCount bytes_in_flight) const {
   DCHECK(InRecovery());
   // Return QuicTime::Zero In order to ensure limited transmit always works.
-  if (prr_out_ == 0) {
+  if (prr_out_ == 0 || bytes_in_flight < kMaxSegmentSize) {
     return QuicTime::Delta::Zero();
   }
   if (SendWindow() > bytes_in_flight) {
     // During PRR-SSRB, limit outgoing packets to 1 extra MSS per ack, instead
     // of sending the entire available window. This prevents burst retransmits
     // when more packets are lost than the CWND reduction.
     //   limit = MAX(prr_delivered - prr_out, DeliveredData) + MSS
     if (prr_delivered_ + ack_count_since_loss_ * kMaxSegmentSize <= prr_out_) {
       return QuicTime::Delta::Infinite();
     }
     return QuicTime::Delta::Zero();
   }
   // Implement Proportional Rate Reduction (RFC6937)
   // Checks a simplified version of the PRR formula that doesn't use division:
   // AvailableSendWindow =
   //   CEIL(prr_delivered * ssthresh / BytesInFlightAtLoss) - prr_sent
   if (prr_delivered_ * slowstart_threshold_ * kMaxSegmentSize >
           prr_out_ * bytes_in_flight_before_loss_) {
     return QuicTime::Delta::Zero();
   }
   return QuicTime::Delta::Infinite();
 }
 
 CongestionControlType TcpCubicSender::GetCongestionControlType() const {
   return reno_ ? kReno : kCubic;
 }
 
 }  // namespace net