If BBQ1 connection option is set, QUIC BBR(v1 & v2) will use a pacing gain of 2.773 at startup and 0.5 at DRAIN.
Protected by FLAGS_quic_reloadable_flag_quic_bbr2_support_new_startup_pacing_gain.
PiperOrigin-RevId: 457810232
diff --git a/quiche/quic/core/congestion_control/bbr2_sender.cc b/quiche/quic/core/congestion_control/bbr2_sender.cc
index bbfdcbb..c6fab64 100644
--- a/quiche/quic/core/congestion_control/bbr2_sender.cc
+++ b/quiche/quic/core/congestion_control/bbr2_sender.cc
@@ -127,6 +127,13 @@
QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr2_extra_acked_window, 2, 2);
model_.SetMaxAckHeightTrackerWindowLength(40);
}
+ if (GetQuicReloadableFlag(quic_bbr2_support_new_startup_pacing_gain) &&
+ ContainsQuicTag(connection_options, kBBQ1)) {
+ QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr2_support_new_startup_pacing_gain, 2,
+ 2);
+ params_.startup_pacing_gain = 2.773;
+ params_.drain_pacing_gain = 1.0 / params_.drain_cwnd_gain;
+ }
if (ContainsQuicTag(connection_options, kBBQ2)) {
params_.startup_cwnd_gain = 2.885;
params_.drain_cwnd_gain = 2.885;
diff --git a/quiche/quic/core/congestion_control/bbr2_simulator_test.cc b/quiche/quic/core/congestion_control/bbr2_simulator_test.cc
index 343dff9..43645e3 100644
--- a/quiche/quic/core/congestion_control/bbr2_simulator_test.cc
+++ b/quiche/quic/core/congestion_control/bbr2_simulator_test.cc
@@ -617,6 +617,26 @@
EXPECT_APPROX_EQ(params.RTT(), rtt_stats()->min_rtt(), 0.2f);
}
+TEST_F(Bbr2DefaultTopologyTest, SimpleTransferBBQ1) {
+ SetQuicReloadableFlag(quic_bbr2_support_new_startup_pacing_gain, true);
+ SetConnectionOption(kBBQ1);
+ DefaultTopologyParams params;
+ CreateNetwork(params);
+
+ // Transfer 12MB.
+ DoSimpleTransfer(12 * 1024 * 1024, QuicTime::Delta::FromSeconds(35));
+ EXPECT_TRUE(Bbr2ModeIsOneOf({Bbr2Mode::PROBE_BW, Bbr2Mode::PROBE_RTT}));
+
+ EXPECT_APPROX_EQ(params.BottleneckBandwidth(),
+ sender_->ExportDebugState().bandwidth_hi, 0.01f);
+
+ EXPECT_LE(sender_loss_rate_in_packets(), 0.05);
+ // The margin here is high, because the aggregation greatly increases
+ // smoothed rtt.
+ EXPECT_GE(params.RTT() * 4, rtt_stats()->smoothed_rtt());
+ EXPECT_APPROX_EQ(params.RTT(), rtt_stats()->min_rtt(), 0.2f);
+}
+
TEST_F(Bbr2DefaultTopologyTest, SimpleTransferSmallBuffer) {
DefaultTopologyParams params;
params.switch_queue_capacity_in_bdp = 0.5;
diff --git a/quiche/quic/core/congestion_control/bbr_sender.cc b/quiche/quic/core/congestion_control/bbr_sender.cc
index 878b598..99b6a04 100644
--- a/quiche/quic/core/congestion_control/bbr_sender.cc
+++ b/quiche/quic/core/congestion_control/bbr_sender.cc
@@ -230,7 +230,13 @@
if (config.HasClientRequestedIndependentOption(kBBQ1, perspective)) {
set_high_gain(kDerivedHighGain);
set_high_cwnd_gain(kDerivedHighGain);
- set_drain_gain(1.f / kDerivedHighGain);
+ if (GetQuicReloadableFlag(quic_bbr2_support_new_startup_pacing_gain)) {
+ QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr2_support_new_startup_pacing_gain, 1,
+ 2);
+ set_drain_gain(1.0 / kDerivedHighCWNDGain);
+ } else {
+ set_drain_gain(1.f / kDerivedHighGain);
+ }
}
if (config.HasClientRequestedIndependentOption(kBBQ3, perspective)) {
enable_ack_aggregation_during_startup_ = true;
diff --git a/quiche/quic/core/quic_flags_list.h b/quiche/quic/core/quic_flags_list.h
index 8c26b10..e2470d5 100644
--- a/quiche/quic/core/quic_flags_list.h
+++ b/quiche/quic/core/quic_flags_list.h
@@ -17,6 +17,8 @@
QUIC_FLAG(quic_restart_flag_quic_testonly_default_true, true)
// If bytes in flight has dipped below 1.25*MaxBW in the last round, do not exit PROBE_UP due to excess queue buildup.
QUIC_FLAG(quic_reloadable_flag_quic_bbr2_no_probe_up_exit_if_no_queue, true)
+// If true and BBQ1 connection option is set, QUIC BBR will use a pacing gain of 2.773 at startup and 0.5 at DRAIN.
+QUIC_FLAG(quic_reloadable_flag_quic_bbr2_support_new_startup_pacing_gain, true)
// If true, 1) remove all experiments that tunes blackhole detection delay or path degrading delay, and 2) ensure network blackhole delay is at least path degrading delay plus 2 PTOs.
QUIC_FLAG(quic_reloadable_flag_quic_remove_blackhole_detection_experiments, true)
// If true, QUIC Legacy Version Encapsulation will be disabled.
