gfe-relnote: (n/a) In QUIC BBRv1, default enable connection options LRTT and BBQ2, and deprecate unused QUIC connection options BBS1 and BBRS. Protected by --gfe2_reloadable_flag_quic_bbr_default_exit_startup_on_loss.
PiperOrigin-RevId: 304406108
Change-Id: I2e89d9474a09e9d9fb5157f69577f55f7a4176b8
diff --git a/quic/core/congestion_control/bbr_sender.cc b/quic/core/congestion_control/bbr_sender.cc
index ee74d70..8331611 100644
--- a/quic/core/congestion_control/bbr_sender.cc
+++ b/quic/core/congestion_control/bbr_sender.cc
@@ -106,7 +106,8 @@
congestion_window_gain_constant_(
static_cast<float>(GetQuicFlag(FLAGS_quic_bbr_cwnd_gain))),
num_startup_rtts_(kRoundTripsWithoutGrowthBeforeExitingStartup),
- exit_startup_on_loss_(false),
+ exit_startup_on_loss_(
+ GetQuicReloadableFlag(quic_bbr_default_exit_startup_on_loss)),
cycle_current_offset_(0),
last_cycle_start_(QuicTime::Zero()),
is_at_full_bandwidth_(false),
@@ -137,6 +138,10 @@
stats_->slowstart_duration = QuicTimeAccumulator();
}
EnterStartupMode(now);
+ if (exit_startup_on_loss_) {
+ QUIC_RELOADABLE_FLAG_COUNT(quic_bbr_default_exit_startup_on_loss);
+ set_high_cwnd_gain(kDerivedHighCWNDGain);
+ }
}
BbrSender::~BbrSender() {}
@@ -198,8 +203,14 @@
return ProbeRttCongestionWindow();
}
- if (InRecovery() && !(rate_based_startup_ && mode_ == STARTUP)) {
- return std::min(congestion_window_, recovery_window_);
+ if (exit_startup_on_loss_) {
+ if (InRecovery()) {
+ return std::min(congestion_window_, recovery_window_);
+ }
+ } else {
+ if (InRecovery() && !(rate_based_startup_ && mode_ == STARTUP)) {
+ return std::min(congestion_window_, recovery_window_);
+ }
}
return congestion_window_;
@@ -257,13 +268,15 @@
if (config.HasClientRequestedIndependentOption(k2RTT, perspective)) {
num_startup_rtts_ = 2;
}
- if (config.HasClientRequestedIndependentOption(kBBRS, perspective)) {
+ if (!exit_startup_on_loss_ &&
+ config.HasClientRequestedIndependentOption(kBBRS, perspective)) {
slower_startup_ = true;
}
if (config.HasClientRequestedIndependentOption(kBBR3, perspective)) {
drain_to_target_ = true;
}
- if (config.HasClientRequestedIndependentOption(kBBS1, perspective)) {
+ if (!exit_startup_on_loss_ &&
+ config.HasClientRequestedIndependentOption(kBBS1, perspective)) {
rate_based_startup_ = true;
}
if (GetQuicReloadableFlag(quic_bbr_mitigate_overly_large_bandwidth_sample)) {
@@ -290,7 +303,8 @@
set_high_cwnd_gain(kDerivedHighGain);
set_drain_gain(1.f / kDerivedHighGain);
}
- if (config.HasClientRequestedIndependentOption(kBBQ2, perspective)) {
+ if (!exit_startup_on_loss_ &&
+ config.HasClientRequestedIndependentOption(kBBQ2, perspective)) {
set_high_cwnd_gain(kDerivedHighCWNDGain);
}
if (config.HasClientRequestedIndependentOption(kBBQ3, perspective)) {
@@ -824,12 +838,14 @@
}
}
- // Slow the pacing rate in STARTUP once loss has ever been detected.
- const bool has_ever_detected_loss = end_recovery_at_.IsInitialized();
- if (slower_startup_ && has_ever_detected_loss &&
- has_non_app_limited_sample_) {
- pacing_rate_ = kStartupAfterLossGain * BandwidthEstimate();
- return;
+ if (!exit_startup_on_loss_) {
+ // Slow the pacing rate in STARTUP once loss has ever been detected.
+ const bool has_ever_detected_loss = end_recovery_at_.IsInitialized();
+ if (slower_startup_ && has_ever_detected_loss &&
+ has_non_app_limited_sample_) {
+ pacing_rate_ = kStartupAfterLossGain * BandwidthEstimate();
+ return;
+ }
}
// Do not decrease the pacing rate during startup.
@@ -877,7 +893,7 @@
void BbrSender::CalculateRecoveryWindow(QuicByteCount bytes_acked,
QuicByteCount bytes_lost) {
- if (rate_based_startup_ && mode_ == STARTUP) {
+ if (!exit_startup_on_loss_ && rate_based_startup_ && mode_ == STARTUP) {
return;
}
diff --git a/quic/core/congestion_control/bbr_sender.h b/quic/core/congestion_control/bbr_sender.h
index eb8282a..ab5d819 100644
--- a/quic/core/congestion_control/bbr_sender.h
+++ b/quic/core/congestion_control/bbr_sender.h
@@ -324,6 +324,8 @@
const float congestion_window_gain_constant_;
// The number of RTTs to stay in STARTUP mode. Defaults to 3.
QuicRoundTripCount num_startup_rtts_;
+
+ // Latched value of --quic_bbr_default_exit_startup_on_loss.
// If true, exit startup if all of the following conditions are met:
// - 1RTT has passed with no bandwidth increase,
// - Some number of congestion events happened with loss, in the last round.
diff --git a/quic/core/congestion_control/bbr_sender_test.cc b/quic/core/congestion_control/bbr_sender_test.cc
index 6f91153..e07931b 100644
--- a/quic/core/congestion_control/bbr_sender_test.cc
+++ b/quic/core/congestion_control/bbr_sender_test.cc
@@ -340,45 +340,6 @@
EXPECT_APPROX_EQ(kTestRtt, sender_->GetMinRtt(), 0.2f);
}
-TEST_F(BbrSenderTest, SimpleTransferEarlyPacketLoss) {
- SetQuicReloadableFlag(quic_bbr_no_bytes_acked_in_startup_recovery, true);
- // Enable rate based startup so the recovery window doesn't hide the true
- // congestion_window_ in GetCongestionWindow().
- SetConnectionOption(kBBS1);
- // Disable Ack Decimation on the receiver, because it can increase srtt.
- QuicConnectionPeer::SetAckMode(receiver_.connection(), AckMode::TCP_ACKING);
- CreateDefaultSetup();
-
- // At startup make sure we are at the default.
- EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
- // Verify that Sender is in slow start.
- EXPECT_TRUE(sender_->InSlowStart());
- // At startup make sure we can send.
- EXPECT_TRUE(sender_->CanSend(0));
- // And that window is un-affected.
- EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
-
- // Transfer 12MB.
- bbr_sender_.AddBytesToTransfer(12 * 1024 * 1024);
- // Drop the first packet.
- receiver_.DropNextIncomingPacket();
- bool simulator_result = simulator_.RunUntilOrTimeout(
- [this]() {
- if (sender_->InRecovery()) {
- // Two packets are acked before the first is declared lost.
- EXPECT_LE(sender_->GetCongestionWindow(),
- (kDefaultWindowTCP + 2 * kDefaultTCPMSS));
- }
- return bbr_sender_.bytes_to_transfer() == 0 || !sender_->InSlowStart();
- },
- QuicTime::Delta::FromSeconds(30));
- EXPECT_TRUE(simulator_result) << "Simple transfer failed. Bytes remaining: "
- << bbr_sender_.bytes_to_transfer();
- EXPECT_EQ(BbrSender::DRAIN, sender_->ExportDebugState().mode);
- EXPECT_EQ(1u, bbr_sender_.connection()->GetStats().packets_lost);
- EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
-}
-
TEST_F(BbrSenderTest, RemoveBytesLostInRecovery) {
SetQuicReloadableFlag(quic_bbr_one_mss_conservation, false);
// Disable Ack Decimation on the receiver, because it can increase srtt.
@@ -706,10 +667,18 @@
ASSERT_EQ(BbrSender::DRAIN, sender_->ExportDebugState().mode);
EXPECT_APPROX_EQ(sender_->BandwidthEstimate() * (1 / 2.885f),
sender_->PacingRate(0), 0.01f);
- // BBR uses CWND gain of 2.88 during STARTUP, hence it will fill the buffer
- // with approximately 1.88 BDPs. Here, we use 1.5 to give some margin for
- // error.
- EXPECT_GE(queue->bytes_queued(), 1.5 * kTestBdp);
+
+ if (!GetQuicReloadableFlag(quic_bbr_default_exit_startup_on_loss)) {
+ // BBR uses CWND gain of 2.88 during STARTUP, hence it will fill the buffer
+ // with approximately 1.88 BDPs. Here, we use 1.5 to give some margin for
+ // error.
+ EXPECT_GE(queue->bytes_queued(), 1.5 * kTestBdp);
+ } else {
+ // BBR uses CWND gain of 2 during STARTUP, hence it will fill the buffer
+ // with approximately 1 BDP. Here, we use 0.8 to give some margin for
+ // error.
+ EXPECT_GE(queue->bytes_queued(), 0.8 * kTestBdp);
+ }
// Observe increased RTT due to bufferbloat.
const QuicTime::Delta queueing_delay =
@@ -843,12 +812,12 @@
DriveOutOfStartup();
const QuicTime::Delta timeout = QuicTime::Delta::FromSeconds(5);
- bool simulator_result;
-
- // Start a few cycles prior to the high gain one.
- simulator_result = simulator_.RunUntilOrTimeout(
- [this]() { return sender_->ExportDebugState().gain_cycle_index == 6; },
- timeout);
+ while (!(sender_->ExportDebugState().gain_cycle_index >= 4 &&
+ bbr_sender_.bytes_to_transfer() == 0)) {
+ bbr_sender_.AddBytesToTransfer(kTestLinkBandwidth.ToBytesPerSecond());
+ ASSERT_TRUE(simulator_.RunUntilOrTimeout(
+ [this]() { return bbr_sender_.bytes_to_transfer() == 0; }, timeout));
+ }
// Send at 10% of available rate. Run for 3 seconds, checking in the middle
// and at the end. The pacing gain should be high throughout.
@@ -867,10 +836,10 @@
// PROBE_BW mode to enter low gain cycle, and exit it earlier than one min_rtt
// due to running out of data to send.
bbr_sender_.AddBytesToTransfer(1.3 * kTestBdp);
- simulator_result = simulator_.RunUntilOrTimeout(
+ ASSERT_TRUE(simulator_.RunUntilOrTimeout(
[this]() { return sender_->ExportDebugState().gain_cycle_index == 1; },
- timeout);
- ASSERT_TRUE(simulator_result);
+ timeout));
+
simulator_.RunFor(0.75 * sender_->ExportDebugState().min_rtt);
EXPECT_EQ(BbrSender::PROBE_BW, sender_->ExportDebugState().mode);
EXPECT_EQ(2, sender_->ExportDebugState().gain_cycle_index);
@@ -963,11 +932,13 @@
EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
}
-// Test exiting STARTUP earlier upon loss due to the LRTT connection option.
-TEST_F(BbrSenderTest, SimpleTransferLRTTStartup) {
+// Test exiting STARTUP earlier upon loss.
+TEST_F(BbrSenderTest, SimpleTransferExitStartupOnLoss) {
CreateDefaultSetup();
- SetConnectionOption(kLRTT);
+ if (!GetQuicReloadableFlag(quic_bbr_default_exit_startup_on_loss)) {
+ SetConnectionOption(kLRTT);
+ }
EXPECT_EQ(3u, sender_->num_startup_rtts());
// Run until the full bandwidth is reached and check how many rounds it was.
@@ -991,11 +962,13 @@
EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
}
-// Test exiting STARTUP earlier upon loss due to the LRTT connection option.
-TEST_F(BbrSenderTest, SimpleTransferLRTTStartupSmallBuffer) {
+// Test exiting STARTUP earlier upon loss with a small buffer.
+TEST_F(BbrSenderTest, SimpleTransferExitStartupOnLossSmallBuffer) {
CreateSmallBufferSetup();
- SetConnectionOption(kLRTT);
+ if (!GetQuicReloadableFlag(quic_bbr_default_exit_startup_on_loss)) {
+ SetConnectionOption(kLRTT);
+ }
EXPECT_EQ(3u, sender_->num_startup_rtts());
// Run until the full bandwidth is reached and check how many rounds it was.
@@ -1019,68 +992,6 @@
EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
}
-// Test slower pacing after loss in STARTUP due to the BBRS connection option.
-TEST_F(BbrSenderTest, SimpleTransferSlowerStartup) {
- CreateSmallBufferSetup();
-
- SetConnectionOption(kBBRS);
- EXPECT_EQ(3u, sender_->num_startup_rtts());
-
- // Run until the full bandwidth is reached and check how many rounds it was.
- bbr_sender_.AddBytesToTransfer(12 * 1024 * 1024);
- QuicRoundTripCount max_bw_round = 0;
- QuicBandwidth max_bw(QuicBandwidth::Zero());
- bool simulator_result = simulator_.RunUntilOrTimeout(
- [this, &max_bw, &max_bw_round]() {
- if (max_bw < sender_->ExportDebugState().max_bandwidth) {
- max_bw = sender_->ExportDebugState().max_bandwidth;
- max_bw_round = sender_->ExportDebugState().round_trip_count;
- }
- // Expect the pacing rate in STARTUP to decrease once packet loss
- // is observed, but the CWND does not.
- if (bbr_sender_.connection()->GetStats().packets_lost > 0 &&
- !sender_->ExportDebugState().is_at_full_bandwidth &&
- sender_->has_non_app_limited_sample()) {
- EXPECT_EQ(1.5f * max_bw, sender_->PacingRate(0));
- }
- return sender_->ExportDebugState().is_at_full_bandwidth;
- },
- QuicTime::Delta::FromSeconds(5));
- ASSERT_TRUE(simulator_result);
- EXPECT_EQ(BbrSender::DRAIN, sender_->ExportDebugState().mode);
- EXPECT_GE(3u, sender_->ExportDebugState().round_trip_count - max_bw_round);
- EXPECT_EQ(3u, sender_->ExportDebugState().rounds_without_bandwidth_gain);
- EXPECT_NE(0u, bbr_sender_.connection()->GetStats().packets_lost);
- EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
-}
-
-// Ensures no change in congestion window in STARTUP after loss.
-TEST_F(BbrSenderTest, SimpleTransferNoConservationInStartup) {
- CreateSmallBufferSetup();
-
- SetConnectionOption(kBBS1);
-
- // Run until the full bandwidth is reached and check how many rounds it was.
- bbr_sender_.AddBytesToTransfer(12 * 1024 * 1024);
- bool used_conservation_cwnd = false;
- bool simulator_result = simulator_.RunUntilOrTimeout(
- [this, &used_conservation_cwnd]() {
- if (!sender_->ExportDebugState().is_at_full_bandwidth &&
- sender_->GetCongestionWindow() <
- sender_->ExportDebugState().congestion_window) {
- used_conservation_cwnd = true;
- }
- return sender_->ExportDebugState().is_at_full_bandwidth;
- },
- QuicTime::Delta::FromSeconds(5));
- ASSERT_TRUE(simulator_result);
- EXPECT_FALSE(used_conservation_cwnd);
- EXPECT_EQ(BbrSender::DRAIN, sender_->ExportDebugState().mode);
- EXPECT_EQ(3u, sender_->ExportDebugState().rounds_without_bandwidth_gain);
- EXPECT_NE(0u, bbr_sender_.connection()->GetStats().packets_lost);
- EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
-}
-
TEST_F(BbrSenderTest, DerivedPacingGainStartup) {
CreateDefaultSetup();
@@ -1111,7 +1022,9 @@
TEST_F(BbrSenderTest, DerivedCWNDGainStartup) {
CreateSmallBufferSetup();
- SetConnectionOption(kBBQ2);
+ if (!GetQuicReloadableFlag(quic_bbr_default_exit_startup_on_loss)) {
+ SetConnectionOption(kBBQ2);
+ }
EXPECT_EQ(3u, sender_->num_startup_rtts());
// Verify that Sender is in slow start.
EXPECT_TRUE(sender_->InSlowStart());
@@ -1128,7 +1041,9 @@
QuicTime::Delta::FromSeconds(5));
ASSERT_TRUE(simulator_result);
EXPECT_EQ(BbrSender::DRAIN, sender_->ExportDebugState().mode);
- EXPECT_EQ(3u, sender_->ExportDebugState().rounds_without_bandwidth_gain);
+ if (!bbr_sender_.connection()->GetStats().bbr_exit_startup_due_to_loss) {
+ EXPECT_EQ(3u, sender_->ExportDebugState().rounds_without_bandwidth_gain);
+ }
EXPECT_APPROX_EQ(kTestLinkBandwidth,
sender_->ExportDebugState().max_bandwidth, 0.01f);
float loss_rate =
diff --git a/quic/core/crypto/crypto_protocol.h b/quic/core/crypto/crypto_protocol.h
index 8e03bb3..8af8a04 100644
--- a/quic/core/crypto/crypto_protocol.h
+++ b/quic/core/crypto/crypto_protocol.h
@@ -82,8 +82,7 @@
const QuicTag k1RTT = TAG('1', 'R', 'T', 'T'); // STARTUP in BBR for 1 RTT
const QuicTag k2RTT = TAG('2', 'R', 'T', 'T'); // STARTUP in BBR for 2 RTTs
const QuicTag kLRTT = TAG('L', 'R', 'T', 'T'); // Exit STARTUP in BBR on loss
-const QuicTag kBBS1 = TAG('B', 'B', 'S', '1'); // Rate-based recovery in
- // BBR STARTUP
+const QuicTag kBBS1 = TAG('B', 'B', 'S', '1'); // DEPRECATED
const QuicTag kBBS2 = TAG('B', 'B', 'S', '2'); // More aggressive packet
// conservation in BBR STARTUP
const QuicTag kBBS3 = TAG('B', 'B', 'S', '3'); // Slowstart packet
@@ -99,8 +98,7 @@
const QuicTag kBBR5 = TAG('B', 'B', 'R', '5'); // 40 RTT ack aggregation
const QuicTag kBBR9 = TAG('B', 'B', 'R', '9'); // Ignore app-limited calls in
// BBR if enough inflight.
-const QuicTag kBBRS = TAG('B', 'B', 'R', 'S'); // Use 1.5x pacing in startup
- // after a loss has occurred.
+const QuicTag kBBRS = TAG('B', 'B', 'R', 'S'); // DEPRECATED
const QuicTag kBBQ1 = TAG('B', 'B', 'Q', '1'); // BBR with lower 2.77 STARTUP
// pacing and CWND gain.
const QuicTag kBBQ2 = TAG('B', 'B', 'Q', '2'); // BBR with lower 2.0 STARTUP
