Change QUIC's Reno congestion controller to use a higher beta. Fixed

net/quic/congestion_control/tcp_cubic_sender_test.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 <algorithm>
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "net/quic/congestion_control/rtt_stats.h"
 #include "net/quic/congestion_control/tcp_cubic_sender.h"
 #include "net/quic/congestion_control/tcp_receiver.h"
 #include "net/quic/crypto/crypto_protocol.h"
 #include "net/quic/quic_utils.h"
 #include "net/quic/test_tools/mock_clock.h"
 #include "net/quic/test_tools/quic_config_peer.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using std::make_pair;
 using std::min;
 
 namespace net {
 namespace test {
 
 const int64 kInitialCongestionWindow = 10;
 const uint32 kDefaultWindowTCP = kInitialCongestionWindow * kDefaultTCPMSS;
+const float kRenoBeta = 0.7f;  // Reno backoff factor.
 
 // TODO(ianswett): Remove 10000 once b/10075719 is fixed.
 const QuicPacketCount kDefaultMaxCongestionWindowTCP = 10000;
 
 class TcpCubicSenderPeer : public TcpCubicSender {
  public:
   TcpCubicSenderPeer(const QuicClock* clock,
                      bool reno,
                      QuicPacketCount max_tcp_congestion_window)
       : TcpCubicSender(
@@ skipping 221 matching lines @@
     SendAvailableSendWindow();
     AckNPackets(2);
   }
   SendAvailableSendWindow();
   QuicByteCount expected_send_window = kDefaultWindowTCP +
       (kDefaultTCPMSS * 2 * kNumberOfAcks);
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   // Lose a packet to exit slow start.
   LoseNPackets(1);
+  size_t packets_in_recovery_window = expected_send_window / kDefaultTCPMSS;
 
-  // We should now have fallen out of slow start.
-  // We expect window to be cut in half by Reno.
-  expected_send_window /= 2;
+  // We should now have fallen out of slow start with a reduced window.
+  expected_send_window *= kRenoBeta;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
-  // Testing Reno phase.
-  // We need to ack half of the pending packet before we can send again.
+  // Recovery phase. We need to ack every packet in the recovery window before
+  // we exit recovery.
   size_t number_of_packets_in_window = expected_send_window / kDefaultTCPMSS;
-  AckNPackets(number_of_packets_in_window);
+  DVLOG(1) << "number_packets: " << number_of_packets_in_window;
+  AckNPackets(packets_in_recovery_window);
+  SendAvailableSendWindow();
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
-  // We need to ack every packet in the window before we exit recovery.
-  for (size_t i = 0; i < number_of_packets_in_window; ++i) {
-    AckNPackets(1);
-    SendAvailableSendWindow();
-    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
-  }
+  // We need to ack an entire window before we increase CWND by 1.
+  AckNPackets(number_of_packets_in_window - 2);
+  SendAvailableSendWindow();
+  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
-  // We need to ack another window before we increase CWND by 1.
-  for (size_t i = 0; i < number_of_packets_in_window - 2; ++i) {
-    AckNPackets(1);
-    SendAvailableSendWindow();
-    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
-  }
-
+  // Next ack should increase cwnd by 1.
   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());
 }
 
@@ skipping 20 matching lines @@
     SendAvailableSendWindow();
     AckNPackets(2);
   }
   SendAvailableSendWindow();
   QuicByteCount expected_send_window = kDefaultWindowTCP +
       (kDefaultTCPMSS * 2 * kNumberOfAcks);
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   LoseNPackets(1);
 
-  // We should now have fallen out of slow start.
-  // We expect window to be cut in half by Reno.
-  expected_send_window /= 2;
+  // We should now have fallen out of slow start with a reduced window.
+  size_t send_window_before_loss = expected_send_window;
+  expected_send_window *= kRenoBeta;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   // Testing TCP proportional rate reduction.
-  // We should send one packet for every two received acks over the remaining
-  // 18 outstanding packets.
-  size_t number_of_packets_in_window = expected_send_window / kDefaultTCPMSS;
-  // The number of packets before we exit recovery is the original CWND minus
-  // the packet that has been lost and the one which triggered the loss.
-  size_t remaining_packets_in_recovery = number_of_packets_in_window * 2 - 1;
-  for (size_t i = 0; i < remaining_packets_in_recovery - 1; i += 2) {
-    AckNPackets(2);
-    EXPECT_TRUE(sender_->TimeUntilSend(
-        clock_.Now(), bytes_in_flight_, HAS_RETRANSMITTABLE_DATA).IsZero());
-    EXPECT_EQ(1, SendAvailableSendWindow());
+  // We should send packets paced over the received acks for the remaining
+  // outstanding packets. The number of packets before we exit recovery is the
+  // original CWND minus the packet that has been lost and the one which
+  // triggered the loss.
+  size_t remaining_packets_in_recovery =
+      send_window_before_loss / kDefaultTCPMSS - 2;
+
+  for (size_t i = 0; i < remaining_packets_in_recovery; ++i) {
+    AckNPackets(1);
+    SendAvailableSendWindow();
     EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
   }
 
   // We need to ack another window before we increase CWND by 1.
+  size_t number_of_packets_in_window = expected_send_window / kDefaultTCPMSS;
   for (size_t i = 0; i < number_of_packets_in_window; ++i) {
     AckNPackets(1);
     EXPECT_EQ(1, SendAvailableSendWindow());
     EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
   }
 
   AckNPackets(1);
   expected_send_window += kDefaultTCPMSS;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 }
 
 TEST_F(TcpCubicSenderTest, SlowStartBurstPacketLossPRR) {
   sender_->SetNumEmulatedConnections(1);
   // Test based on the second example in RFC6937, though we also implement
   // forward acknowledgements, so the first two incoming acks will trigger
   // PRR immediately.
-  // Ack 10 packets in 5 acks to raise the CWND to 20, as in the example.
-  const int kNumberOfAcks = 5;
+  // Ack 20 packets in 10 acks to raise the CWND to 30.
+  const int kNumberOfAcks = 10;
   for (int i = 0; i < kNumberOfAcks; ++i) {
     // Send our full send window.
     SendAvailableSendWindow();
     AckNPackets(2);
   }
   SendAvailableSendWindow();
   QuicByteCount expected_send_window = kDefaultWindowTCP +
       (kDefaultTCPMSS * 2 * kNumberOfAcks);
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
-  // Ack a packet with a 15 packet gap, losing 13 of them due to FACK.
-  LoseNPackets(13);
+  // Lose one more than the congestion window reduction, so that after loss,
+  // bytes_in_flight is lesser than the congestion window.
+  size_t send_window_after_loss = kRenoBeta * expected_send_window;
+  size_t num_packets_to_lose =
+      (expected_send_window - send_window_after_loss) / kDefaultTCPMSS + 1;
+  LoseNPackets(num_packets_to_lose);
   // Immediately after the loss, ensure at least one packet can be sent.
   // Losses without subsequent acks can occur with timer based loss detection.
   EXPECT_TRUE(sender_->TimeUntilSend(
       clock_.Now(), bytes_in_flight_, HAS_RETRANSMITTABLE_DATA).IsZero());
   AckNPackets(1);
 
-  // We should now have fallen out of slow start.
-  // We expect window to be cut in half by Reno.
-  expected_send_window /= 2;
+  // We should now have fallen out of slow start with a reduced window.
+  expected_send_window *= kRenoBeta;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   // Only 2 packets should be allowed to be sent, per PRR-SSRB
   EXPECT_EQ(2, SendAvailableSendWindow());
 
   // Ack the next packet, which triggers another loss.
   LoseNPackets(1);
   AckNPackets(1);
 
   // Send 2 packets to simulate PRR-SSRB.
   EXPECT_EQ(2, SendAvailableSendWindow());
 
   // Ack the next packet, which triggers another loss.
   LoseNPackets(1);
   AckNPackets(1);
 
   // Send 2 packets to simulate PRR-SSRB.
   EXPECT_EQ(2, SendAvailableSendWindow());
 
-  AckNPackets(1);
-  EXPECT_EQ(2, SendAvailableSendWindow());
-
-  AckNPackets(1);
-  EXPECT_EQ(2, SendAvailableSendWindow());
-
-  // The window should not have changed.
-  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
-
   // Exit recovery and return to sending at the new rate.
   for (int i = 0; i < kNumberOfAcks; ++i) {
     AckNPackets(1);
     EXPECT_EQ(1, SendAvailableSendWindow());
   }
 }
 
 TEST_F(TcpCubicSenderTest, RTOCongestionWindowAndRevert) {
   EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
   EXPECT_EQ(10000u, sender_->slowstart_threshold());
@@ skipping 171 matching lines @@
     SendAvailableSendWindow();
     AckNPackets(2);
   }
   SendAvailableSendWindow();
   QuicByteCount expected_send_window = kDefaultWindowTCP +
       (kDefaultTCPMSS * 2 * kNumberOfAcks);
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   LoseNPackets(1);
 
-  // We should now have fallen out of slow start, and window should be cut in
-  // half by Reno. New cwnd should be 10.
-  expected_send_window /= 2;
+  // We should now have fallen out of slow start with a reduced window.
+  expected_send_window *= kRenoBeta;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   // No congestion window growth should occur in recovery phase, i.e., until the
   // currently outstanding 20 packets are acked.
   for (int i = 0; i < 10; ++i) {
     // Send our full send window.
     SendAvailableSendWindow();
     EXPECT_TRUE(sender_->InRecovery());
     AckNPackets(2);
     EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
   }
   EXPECT_FALSE(sender_->InRecovery());
 
   // Out of recovery now. Congestion window should not grow for half an RTT.
+  size_t packets_in_send_window = expected_send_window / kDefaultTCPMSS;
+  SendAvailableSendWindow();
+  AckNPackets(packets_in_send_window / 2 - 2);
+  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
+
+  // Next ack should increase congestion window by 1MSS.
   SendAvailableSendWindow();
   AckNPackets(2);
+  expected_send_window += kDefaultTCPMSS;
+  packets_in_send_window += 1;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
-  // Next ack will be the 5th and should increase congestion window by 1MSS.
+  // Congestion window should remain steady again for half an RTT.
+  SendAvailableSendWindow();
+  AckNPackets(packets_in_send_window / 2 - 1);
+  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
+
+  // Next ack should cause congestion window to grow by 1MSS.
+  SendAvailableSendWindow();
   AckNPackets(2);
   expected_send_window += kDefaultTCPMSS;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
-
-  for (int i = 0; i < 2; ++i) {
-    SendAvailableSendWindow();
-    AckNPackets(2);
-    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
-  }
-
-  // Next ack should cause congestion window to grow by 1MSS.
-  AckNPackets(2);
-  expected_send_window += kDefaultTCPMSS;
-  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 }
 
 TEST_F(TcpCubicSenderTest, 1ConnectionCongestionAvoidanceAtEndOfRecovery) {
   sender_->SetNumEmulatedConnections(1);
   // Ack 10 packets in 5 acks to raise the CWND to 20.
   const int kNumberOfAcks = 5;
   for (int i = 0; i < kNumberOfAcks; ++i) {
     // Send our full send window.
     SendAvailableSendWindow();
     AckNPackets(2);
   }
   SendAvailableSendWindow();
   QuicByteCount expected_send_window = kDefaultWindowTCP +
       (kDefaultTCPMSS * 2 * kNumberOfAcks);
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   LoseNPackets(1);
 
-  // We should now have fallen out of slow start, and window should be cut in
-  // half by Reno. New cwnd should be 10.
-  expected_send_window /= 2;
+  // We should now have fallen out of slow start with a reduced window.
+  expected_send_window *= kRenoBeta;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 
   // No congestion window growth should occur in recovery phase, i.e., until the
   // currently outstanding 20 packets are acked.
   for (int i = 0; i < 10; ++i) {
     // Send our full send window.
     SendAvailableSendWindow();
     EXPECT_TRUE(sender_->InRecovery());
     AckNPackets(2);
     EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
   }
   EXPECT_FALSE(sender_->InRecovery());
 
   // Out of recovery now. Congestion window should not grow during RTT.
-  for (int i = 0; i < 4; ++i) {
+  for (uint64 i = 0; i < expected_send_window / kDefaultTCPMSS - 2; i += 2) {
     // Send our full send window.
     SendAvailableSendWindow();
     AckNPackets(2);
     EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
   }
 
   // Next ack should cause congestion window to grow by 1MSS.
+  SendAvailableSendWindow();
   AckNPackets(2);
   expected_send_window += kDefaultTCPMSS;
   EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
 }
 
 }  // namespace test
 }  // namespace net