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

net/quic/congestion_control/tcp_cubic_sender_bytes_test.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 "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 42 matching lines @@
 class TcpCubicSenderBytesTest : public ::testing::Test {
  protected:
   TcpCubicSenderBytesTest()
       : one_ms_(QuicTime::Delta::FromMilliseconds(1)),
         sender_(new TcpCubicSenderBytesPeer(&clock_, true)),
         packet_number_(1),
         acked_packet_number_(0),
         bytes_in_flight_(0) {}
 
   int SendAvailableSendWindow() {
+    return SendAvailableSendWindow(kDefaultTCPMSS);
+  }
+
+  int SendAvailableSendWindow(QuicPacketLength packet_length) {
     // Send as long as TimeUntilSend returns Zero.
     int packets_sent = 0;
     bool can_send =
         sender_->TimeUntilSend(clock_.Now(), bytes_in_flight_).IsZero();
     while (can_send) {
       sender_->OnPacketSent(clock_.Now(), bytes_in_flight_, packet_number_++,
                             kDefaultTCPMSS, HAS_RETRANSMITTABLE_DATA);
       ++packets_sent;
       bytes_in_flight_ += kDefaultTCPMSS;
       can_send =
@@ skipping 12 matching lines @@
       ++acked_packet_number_;
       acked_packets.push_back(
           std::make_pair(acked_packet_number_, kDefaultTCPMSS));
     }
     sender_->OnCongestionEvent(true, bytes_in_flight_, acked_packets,
                                lost_packets);
     bytes_in_flight_ -= n * kDefaultTCPMSS;
     clock_.AdvanceTime(one_ms_);
   }
 
-  void LoseNPackets(int n) {
+  void LoseNPackets(int n) { LoseNPackets(n, kDefaultTCPMSS); }
+
+  void LoseNPackets(int n, QuicPacketLength packet_length) {
     SendAlgorithmInterface::CongestionVector acked_packets;
     SendAlgorithmInterface::CongestionVector lost_packets;
     for (int i = 0; i < n; ++i) {
       ++acked_packet_number_;
       lost_packets.push_back(
-          std::make_pair(acked_packet_number_, kDefaultTCPMSS));
+          std::make_pair(acked_packet_number_, packet_length));
     }
     sender_->OnCongestionEvent(false, bytes_in_flight_, acked_packets,
                                lost_packets);
-    bytes_in_flight_ -= n * kDefaultTCPMSS;
+    bytes_in_flight_ -= n * packet_length;
   }
 
   // Does not increment acked_packet_number_.
   void LosePacket(QuicPacketNumber packet_number) {
     SendAlgorithmInterface::CongestionVector acked_packets;
     SendAlgorithmInterface::CongestionVector lost_packets;
     lost_packets.push_back(std::make_pair(packet_number, kDefaultTCPMSS));
     sender_->OnCongestionEvent(false, bytes_in_flight_, acked_packets,
                                lost_packets);
     bytes_in_flight_ -= kDefaultTCPMSS;
@@ skipping 157 matching lines @@
   AckNPackets(1);
   expected_send_window += kDefaultTCPMSS;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   // Now RTO and ensure slow start gets reset.
   EXPECT_TRUE(sender_->hybrid_slow_start().started());
   sender_->OnRetransmissionTimeout(true);
   EXPECT_FALSE(sender_->hybrid_slow_start().started());
 }
 
+TEST_F(TcpCubicSenderBytesTest, SlowStartHalfPacketLossWithLargeReduction) {
+  FLAGS_quic_sslr_byte_conservation = true;
+  QuicConfig config;
+  QuicTagVector options;
+  options.push_back(kSSLR);
+  QuicConfigPeer::SetReceivedConnectionOptions(&config, options);
+  sender_->SetFromConfig(config, Perspective::IS_SERVER);
+
+  sender_->SetNumEmulatedConnections(1);
+  const int kNumberOfAcks = 10;
+  for (int i = 0; i < kNumberOfAcks; ++i) {
+    // Send our full send window in half sized packets.
+    SendAvailableSendWindow(kDefaultTCPMSS / 2);
+    AckNPackets(2);
+  }
+  SendAvailableSendWindow(kDefaultTCPMSS / 2);
+  QuicByteCount expected_send_window =
+      kDefaultWindowTCP + (kDefaultTCPMSS * 2 * kNumberOfAcks);
+  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
+
+  // Lose a packet to exit slow start. We should now have fallen out of
+  // slow start with a window reduced by 1.
+  LoseNPackets(1);
+  expected_send_window -= kDefaultTCPMSS;
+  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
+
+  // Lose 10 packets in recovery and verify that congestion window is reduced
+  // by 5 packets.
+  LoseNPackets(10, kDefaultTCPMSS / 2);
+  expected_send_window -= 5 * kDefaultTCPMSS;
+  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
+}
+
 TEST_F(TcpCubicSenderBytesTest, NoPRRWhenLessThanOnePacketInFlight) {
   SendAvailableSendWindow();
   LoseNPackets(kInitialCongestionWindowPackets - 1);
   AckNPackets(1);
   // PRR will allow 2 packets for every ack during recovery.
   EXPECT_EQ(2, SendAvailableSendWindow());
   // Simulate abandoning all packets by supplying a bytes_in_flight of 0.
   // PRR should now allow a packet to be sent, even though prr's state variables
   // believe it has sent enough packets.
   EXPECT_EQ(QuicTime::Delta::Zero(), sender_->TimeUntilSend(clock_.Now(), 0));
@@ skipping 425 matching lines @@
   // Resets cwnd and slow start threshold on connection migrations.
   sender_->OnConnectionMigration();
   EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
   EXPECT_EQ(kMaxCongestionWindow * kDefaultTCPMSS,
             sender_->GetSlowStartThreshold());
   EXPECT_FALSE(sender_->hybrid_slow_start().started());
 }
 
 }  // namespace test
 }  // namespace net