relnote: Protected by --quic_fix_cubic_bytes_quantization. Fix CubicBytes Quantization.

net/quic/core/congestion_control/cubic_bytes_test.cc

Index: net/quic/core/congestion_control/cubic_bytes_test.cc
diff --git a/net/quic/core/congestion_control/cubic_bytes_test.cc b/net/quic/core/congestion_control/cubic_bytes_test.cc
index 0ee3b43c993f7b3595471c53fd7ef72ba094325e..529af4f9b0d9fce4a9c5f5abd6685eb828bab4bd 100644
--- a/net/quic/core/congestion_control/cubic_bytes_test.cc
+++ b/net/quic/core/congestion_control/cubic_bytes_test.cc
@@ -20,14 +20,16 @@ const float kNConnectionBeta = (kNumConnections - 1 + kBeta) / kNumConnections;
 const float kNConnectionAlpha = 3 * kNumConnections * kNumConnections *
                                 (1 - kNConnectionBeta) / (1 + kNConnectionBeta);
 
-class CubicBytesTest : public ::testing::TestWithParam<bool> {
+class CubicBytesTest : public ::testing::Test {
  protected:
   CubicBytesTest()
       : one_ms_(QuicTime::Delta::FromMilliseconds(1)),
         hundred_ms_(QuicTime::Delta::FromMilliseconds(100)),
-        cubic_(&clock_),
-        fix_convex_mode_(GetParam()) {
-    cubic_.SetFixConvexMode(fix_convex_mode_);
+        cubic_(&clock_) {
+    cubic_.SetFixConvexMode(
+        FLAGS_quic_fix_cubic_convex_mode);
+    cubic_.SetFixCubicQuantization(
+        FLAGS_quic_fix_cubic_bytes_quantization);
   }
 
   QuicByteCount RenoCwndInBytes(QuicByteCount current_cwnd) {
@@ -43,11 +45,14 @@ class CubicBytesTest : public ::testing::TestWithParam<bool> {
   }
 
   QuicByteCount CubicConvexCwndInBytes(QuicByteCount initial_cwnd,
-                                       int64_t rtt_ms,
-                                       int64_t elapsed_time_ms) {
-    const int64_t offset = ((elapsed_time_ms + rtt_ms) << 10) / 1000;
+                                       QuicTime::Delta rtt,
+                                       QuicTime::Delta elapsed_time) {
+    const int64_t offset =
+        ((elapsed_time + rtt).ToMicroseconds() << 10) / 1000000;
     const QuicByteCount delta_congestion_window =
-        ((410 * offset * offset * offset) >> 40) * kDefaultTCPMSS;
+        FLAGS_quic_fix_cubic_bytes_quantization
+            ? ((410 * offset * offset * offset) * kDefaultTCPMSS >> 40)
+            : ((410 * offset * offset * offset) >> 40) * kDefaultTCPMSS;
     const QuicByteCount cubic_cwnd = initial_cwnd + delta_congestion_window;
     return cubic_cwnd;
   }
@@ -56,17 +61,14 @@ class CubicBytesTest : public ::testing::TestWithParam<bool> {
   const QuicTime::Delta hundred_ms_;
   MockClock clock_;
   CubicBytes cubic_;
-  bool fix_convex_mode_;
 };
 
-INSTANTIATE_TEST_CASE_P(CubicBytesTests, CubicBytesTest, testing::Bool());
-
 // TODO(jokulik): The original "AboveOrigin" test, below, is very
 // loose.  It's nearly impossible to make the test tighter without
 // deploying the fix for convex mode.  Once cubic convex is deployed,
 // replace "AboveOrigin" with this test.
-TEST_P(CubicBytesTest, AboveOriginWithTighterBounds) {
-  if (!fix_convex_mode_) {
+TEST_F(CubicBytesTest, AboveOriginWithTighterBounds) {
+  if (!FLAGS_quic_fix_cubic_convex_mode) {
     // Without convex mode fixed, the behavior of the algorithm is so
     // far from expected, there's no point in doing a tighter test.
     return;
@@ -89,8 +91,13 @@ TEST_P(CubicBytesTest, AboveOriginWithTighterBounds) {
   // The maximum number of expected Reno RTTs is calculated by
   // finding the point where the cubic curve and the reno curve meet.
   const int max_reno_rtts =
-      std::sqrt(kNConnectionAlpha / (.4 * rtt_min_s * rtt_min_s * rtt_min_s)) -
-      1;
+      FLAGS_quic_fix_cubic_bytes_quantization
+          ? std::sqrt(kNConnectionAlpha /
+                      (.4 * rtt_min_s * rtt_min_s * rtt_min_s)) -
+                2
+          : std::sqrt(kNConnectionAlpha /
+                      (.4 * rtt_min_s * rtt_min_s * rtt_min_s)) -
+                1;
   for (int i = 0; i < max_reno_rtts; ++i) {
     // Alternatively, we expect it to increase by one, every time we
     // receive current_cwnd/Alpha acks back.  (This is another way of
@@ -116,23 +123,23 @@ TEST_P(CubicBytesTest, AboveOriginWithTighterBounds) {
     clock_.AdvanceTime(hundred_ms_);
   }
 
-  // Because our byte-wise Reno under-estimates the cwnd, we switch to
-  // conservative increases for a few acks before switching to true
-  // cubic increases.
-  for (int i = 0; i < 3; ++i) {
-    const QuicByteCount next_expected_cwnd =
-        ConservativeCwndInBytes(current_cwnd);
-    current_cwnd =
-        cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
-    ASSERT_EQ(next_expected_cwnd, current_cwnd);
+  if (!FLAGS_quic_fix_cubic_bytes_quantization) {
+    // Because our byte-wise Reno under-estimates the cwnd, we switch to
+    // conservative increases for a few acks before switching to true
+    // cubic increases.
+    for (int i = 0; i < 3; ++i) {
+      const QuicByteCount next_expected_cwnd =
+          ConservativeCwndInBytes(current_cwnd);
+      current_cwnd = cubic_.CongestionWindowAfterAck(kDefaultTCPMSS,
+                                                     current_cwnd, rtt_min);
+      ASSERT_EQ(next_expected_cwnd, current_cwnd);
+    }
   }
 
   for (int i = 0; i < 54; ++i) {
     const uint64_t max_acks_this_epoch = current_cwnd / kDefaultTCPMSS;
-    const int elapsed_time_ms =
-        (clock_.ApproximateNow() - initial_time).ToMilliseconds();
     const QuicByteCount expected_cwnd = CubicConvexCwndInBytes(
-        initial_cwnd, rtt_min.ToMilliseconds(), elapsed_time_ms);
+        initial_cwnd, rtt_min, (clock_.ApproximateNow() - initial_time));
     current_cwnd =
         cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
     ASSERT_EQ(expected_cwnd, current_cwnd);
@@ -144,24 +151,32 @@ TEST_P(CubicBytesTest, AboveOriginWithTighterBounds) {
     }
     clock_.AdvanceTime(hundred_ms_);
   }
-  const int elapsed_time_ms =
-      (clock_.ApproximateNow() - initial_time).ToMilliseconds();
   const QuicByteCount expected_cwnd = CubicConvexCwndInBytes(
-      initial_cwnd, rtt_min.ToMilliseconds(), elapsed_time_ms);
+      initial_cwnd, rtt_min, (clock_.ApproximateNow() - initial_time));
   current_cwnd =
       cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
   ASSERT_EQ(expected_cwnd, current_cwnd);
 }
 
-TEST_P(CubicBytesTest, AboveOrigin) {
+TEST_F(CubicBytesTest, AboveOrigin) {
+  if (!FLAGS_quic_fix_cubic_convex_mode &&
+      FLAGS_quic_fix_cubic_bytes_quantization) {
+    // Without convex mode fixed, the behavior of the algorithm does
+    // not fit the exact pattern of this test.
+    // TODO(jokulik): Once the convex mode fix becomes default, this
+    // test can be replaced with the better AboveOriginTighterBounds
+    // test.
+    return;
+  }
   // Convex growth.
   const QuicTime::Delta rtt_min = hundred_ms_;
   QuicByteCount current_cwnd = 10 * kDefaultTCPMSS;
   // Without the signed-integer, cubic-convex fix, we start out in the
   // wrong mode.
-  QuicPacketCount expected_cwnd = fix_convex_mode_
-                                      ? RenoCwndInBytes(current_cwnd)
-                                      : ConservativeCwndInBytes(current_cwnd);
+  QuicPacketCount expected_cwnd =
+      FLAGS_quic_fix_cubic_convex_mode
+          ? RenoCwndInBytes(current_cwnd)
+          : ConservativeCwndInBytes(current_cwnd);
   // Initialize the state.
   clock_.AdvanceTime(one_ms_);
   ASSERT_EQ(expected_cwnd, cubic_.CongestionWindowAfterAck(
@@ -180,7 +195,7 @@ TEST_P(CubicBytesTest, AboveOrigin) {
     clock_.AdvanceTime(hundred_ms_);
     current_cwnd =
         cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
-    if (fix_convex_mode_) {
+    if (FLAGS_quic_fix_cubic_convex_mode) {
       // When we fix convex mode and the uint64 arithmetic, we
       // increase the expected_cwnd only after after the first 100ms,
       // rather than after the initial 1ms.
@@ -210,20 +225,72 @@ TEST_P(CubicBytesTest, AboveOrigin) {
       initial_cwnd / kDefaultTCPMSS +
       (elapsed_time_s * elapsed_time_s * elapsed_time_s * 410) / 1024;
   // Without the convex mode fix, the result is off by one.
-  if (!fix_convex_mode_) {
+  if (!FLAGS_quic_fix_cubic_convex_mode) {
     ++expected_cwnd;
   }
   EXPECT_EQ(expected_cwnd, current_cwnd / kDefaultTCPMSS);
 }
 
-TEST_P(CubicBytesTest, LossEvents) {
+// Constructs an artificial scenario to ensure that cubic-convex
+// increases are truly fine-grained:
+//
+// - After starting the epoch, this test advances the elapsed time
+// sufficiently far that cubic will do small increases at less than
+// MaxCubicTimeInterval() intervals.
+//
+// - Sets an artificially large initial cwnd to prevent Reno from the
+// convex increases on every ack.
+TEST_F(CubicBytesTest, AboveOriginFineGrainedCubing) {
+  if (!FLAGS_quic_fix_cubic_convex_mode ||
+      !FLAGS_quic_fix_cubic_bytes_quantization) {
+    // Without these two fixes, this test cannot pass.
+    return;
+  }
+
+  // Start the test with an artificially large cwnd to prevent Reno
+  // from over-taking cubic.
+  QuicByteCount current_cwnd = 1000 * kDefaultTCPMSS;
+  const QuicByteCount initial_cwnd = current_cwnd;
+  const QuicTime::Delta rtt_min = hundred_ms_;
+  clock_.AdvanceTime(one_ms_);
+  QuicTime initial_time = clock_.ApproximateNow();
+
+  // Start the epoch and then artificially advance the time.
+  current_cwnd =
+      cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
+  clock_.AdvanceTime(QuicTime::Delta::FromMilliseconds(600));
+  current_cwnd =
+      cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
+
+  // We expect the algorithm to perform only non-zero, fine-grained cubic
+  // increases on every ack in this case.
+  for (int i = 0; i < 100; ++i) {
+    clock_.AdvanceTime(QuicTime::Delta::FromMilliseconds(10));
+    const QuicByteCount expected_cwnd = CubicConvexCwndInBytes(
+        initial_cwnd, rtt_min, (clock_.ApproximateNow() - initial_time));
+    const QuicByteCount next_cwnd =
+        cubic_.CongestionWindowAfterAck(kDefaultTCPMSS, current_cwnd, rtt_min);
+    // Make sure we are performing cubic increases.
+    ASSERT_EQ(expected_cwnd, next_cwnd);
+    // Make sure that these are non-zero, less-than-packet sized
+    // increases.
+    ASSERT_GT(next_cwnd, current_cwnd);
+    const QuicByteCount cwnd_delta = next_cwnd - current_cwnd;
+    ASSERT_GT(kDefaultTCPMSS * .1, cwnd_delta);
+
+    current_cwnd = next_cwnd;
+  }
+}
+
+TEST_F(CubicBytesTest, LossEvents) {
   const QuicTime::Delta rtt_min = hundred_ms_;
   QuicByteCount current_cwnd = 422 * kDefaultTCPMSS;
   // Without the signed-integer, cubic-convex fix, we mistakenly
   // increment cwnd after only one_ms_ and a single ack.
-  QuicPacketCount expected_cwnd = fix_convex_mode_
-                                      ? RenoCwndInBytes(current_cwnd)
-                                      : current_cwnd + kDefaultTCPMSS / 2;
+  QuicPacketCount expected_cwnd =
+      FLAGS_quic_fix_cubic_convex_mode
+          ? RenoCwndInBytes(current_cwnd)
+          : current_cwnd + kDefaultTCPMSS / 2;
   // Initialize the state.
   clock_.AdvanceTime(one_ms_);
   EXPECT_EQ(expected_cwnd, cubic_.CongestionWindowAfterAck(
@@ -236,15 +303,16 @@ TEST_P(CubicBytesTest, LossEvents) {
             cubic_.CongestionWindowAfterPacketLoss(current_cwnd));
 }
 
-TEST_P(CubicBytesTest, BelowOrigin) {
+TEST_F(CubicBytesTest, BelowOrigin) {
   // Concave growth.
   const QuicTime::Delta rtt_min = hundred_ms_;
   QuicByteCount current_cwnd = 422 * kDefaultTCPMSS;
   // Without the signed-integer, cubic-convex fix, we mistakenly
   // increment cwnd after only one_ms_ and a single ack.
-  QuicPacketCount expected_cwnd = fix_convex_mode_
-                                      ? RenoCwndInBytes(current_cwnd)
-                                      : current_cwnd + kDefaultTCPMSS / 2;
+  QuicPacketCount expected_cwnd =
+      FLAGS_quic_fix_cubic_convex_mode
+          ? RenoCwndInBytes(current_cwnd)
+          : current_cwnd + kDefaultTCPMSS / 2;
   // Initialize the state.
   clock_.AdvanceTime(one_ms_);
   EXPECT_EQ(expected_cwnd, cubic_.CongestionWindowAfterAck(