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

net/quic/core/congestion_control/cubic_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/core/congestion_control/cubic_bytes.h"
 
 #include "base/logging.h"
+#include "net/quic/core/quic_flags.h"
 #include "net/quic/test_tools/mock_clock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
 namespace test {
 
 const float kBeta = 0.7f;  // Default Cubic backoff factor.
 const uint32_t kNumConnections = 2;
 const float kNConnectionBeta = (kNumConnections - 1 + kBeta) / kNumConnections;
 const float kNConnectionAlpha = 3 * kNumConnections * kNumConnections *
                                 (1 - kNConnectionBeta) / (1 + kNConnectionBeta);
 
 class CubicBytesTest : public ::testing::Test {
  protected:
   CubicBytesTest()
       : one_ms_(QuicTime::Delta::FromMilliseconds(1)),
         hundred_ms_(QuicTime::Delta::FromMilliseconds(100)),
         cubic_(&clock_) {}
   const QuicTime::Delta one_ms_;
   const QuicTime::Delta hundred_ms_;
   MockClock clock_;
   CubicBytes cubic_;
 };
 
 TEST_F(CubicBytesTest, AboveOrigin) {
   // Convex growth.
   const QuicTime::Delta rtt_min = hundred_ms_;
   QuicByteCount current_cwnd = 10 * kDefaultTCPMSS;
-  QuicByteCount expected_cwnd = current_cwnd + kDefaultTCPMSS;
+  QuicByteCount expected_cwnd =
+      current_cwnd + (FLAGS_quic_limit_cubic_cwnd_increase ? kDefaultTCPMSS / 2
+                                                           : kDefaultTCPMSS);
   // Initialize the state.
   clock_.AdvanceTime(one_ms_);
   EXPECT_EQ(expected_cwnd, cubic_.CongestionWindowAfterAck(
                                kDefaultTCPMSS, current_cwnd, rtt_min));
   current_cwnd = expected_cwnd;
   // Normal TCP phase.
   for (int i = 0; i < 48; ++i) {
     for (QuicPacketCount n = 1;
          n < current_cwnd / kDefaultTCPMSS / kNConnectionAlpha; ++n) {
       // Call once per ACK.
@@ skipping 23 matching lines @@
   float elapsed_time_s = 10.0f + 0.1f;
   // |expected_cwnd| is initial value of cwnd + K * t^3, where K = 0.4.
   expected_cwnd =
       11 + (elapsed_time_s * elapsed_time_s * elapsed_time_s * 410) / 1024;
   EXPECT_EQ(expected_cwnd, current_cwnd / kDefaultTCPMSS);
 }
 
 TEST_F(CubicBytesTest, LossEvents) {
   const QuicTime::Delta rtt_min = hundred_ms_;
   QuicByteCount current_cwnd = 422 * kDefaultTCPMSS;
-  QuicPacketCount expected_cwnd = current_cwnd + kDefaultTCPMSS;
+  QuicPacketCount expected_cwnd =
+      current_cwnd + (FLAGS_quic_limit_cubic_cwnd_increase ? kDefaultTCPMSS / 2
+                                                           : kDefaultTCPMSS);
   // Initialize the state.
   clock_.AdvanceTime(one_ms_);
   EXPECT_EQ(expected_cwnd, cubic_.CongestionWindowAfterAck(
                                kDefaultTCPMSS, current_cwnd, rtt_min));
   expected_cwnd = static_cast<QuicPacketCount>(current_cwnd * kNConnectionBeta);
   EXPECT_EQ(expected_cwnd,
             cubic_.CongestionWindowAfterPacketLoss(current_cwnd));
   expected_cwnd = static_cast<QuicPacketCount>(current_cwnd * kNConnectionBeta);
   EXPECT_EQ(expected_cwnd,
             cubic_.CongestionWindowAfterPacketLoss(current_cwnd));
 }
 
 TEST_F(CubicBytesTest, BelowOrigin) {
   // Concave growth.
   const QuicTime::Delta rtt_min = hundred_ms_;
   QuicByteCount current_cwnd = 422 * kDefaultTCPMSS;
-  QuicPacketCount expected_cwnd = current_cwnd + kDefaultTCPMSS;
+  QuicPacketCount expected_cwnd =
+      current_cwnd + (FLAGS_quic_limit_cubic_cwnd_increase ? kDefaultTCPMSS / 2
+                                                           : kDefaultTCPMSS);
   // Initialize the state.
   clock_.AdvanceTime(one_ms_);
   EXPECT_EQ(expected_cwnd, cubic_.CongestionWindowAfterAck(
                                kDefaultTCPMSS, current_cwnd, rtt_min));
   expected_cwnd = static_cast<QuicPacketCount>(current_cwnd * kNConnectionBeta);
   EXPECT_EQ(expected_cwnd,
             cubic_.CongestionWindowAfterPacketLoss(current_cwnd));
   current_cwnd = expected_cwnd;
   // First update after loss to initialize the epoch.
   current_cwnd =
       cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
   // Cubic phase.
   for (int i = 0; i < 40; ++i) {
     clock_.AdvanceTime(hundred_ms_);
     current_cwnd =
         cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
   }
-  expected_cwnd = 422 * kDefaultTCPMSS;
+  expected_cwnd =
+      FLAGS_quic_limit_cubic_cwnd_increase ? 553632 : 422 * kDefaultTCPMSS;
   EXPECT_EQ(expected_cwnd, current_cwnd);
 }
 
 }  // namespace test
 }  // namespace net