Support the BBR4 and BBR5 connection options in BBR2 to decrease and increase the extra acked window length.
Protected by quic_reloadable_flag_quic_extra_acked_window.
PiperOrigin-RevId: 400284465
diff --git a/quic/core/congestion_control/bbr2_misc.h b/quic/core/congestion_control/bbr2_misc.h
index fb66b98..a603064 100644
--- a/quic/core/congestion_control/bbr2_misc.h
+++ b/quic/core/congestion_control/bbr2_misc.h
@@ -9,6 +9,7 @@
#include <limits>
#include "quic/core/congestion_control/bandwidth_sampler.h"
+#include "quic/core/congestion_control/send_algorithm_interface.h"
#include "quic/core/congestion_control/windowed_filter.h"
#include "quic/core/quic_bandwidth.h"
#include "quic/core/quic_packet_number.h"
@@ -426,6 +427,10 @@
bandwidth_sampler_.SetLimitMaxAckHeightTrackerBySendRate(value);
}
+ void SetMaxAckHeightTrackerWindowLength(QuicRoundTripCount value) {
+ bandwidth_sampler_.SetMaxAckHeightTrackerWindowLength(value);
+ }
+
bool MaybeExpireMinRtt(const Bbr2CongestionEvent& congestion_event);
QuicBandwidth BandwidthEstimate() const {
diff --git a/quic/core/congestion_control/bbr2_sender.cc b/quic/core/congestion_control/bbr2_sender.cc
index f1c96d6..6938f6d 100644
--- a/quic/core/congestion_control/bbr2_sender.cc
+++ b/quic/core/congestion_control/bbr2_sender.cc
@@ -120,6 +120,16 @@
void Bbr2Sender::ApplyConnectionOptions(
const QuicTagVector& connection_options) {
+ if (GetQuicReloadableFlag(quic_bbr2_extra_acked_window) &&
+ ContainsQuicTag(connection_options, kBBR4)) {
+ QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr2_extra_acked_window, 1, 2);
+ model_.SetMaxAckHeightTrackerWindowLength(20);
+ }
+ if (GetQuicReloadableFlag(quic_bbr2_extra_acked_window) &&
+ ContainsQuicTag(connection_options, kBBR5)) {
+ QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr2_extra_acked_window, 2, 2);
+ model_.SetMaxAckHeightTrackerWindowLength(40);
+ }
if (ContainsQuicTag(connection_options, kBBQ2)) {
params_.startup_cwnd_gain = 2.885;
params_.drain_cwnd_gain = 2.885;
diff --git a/quic/core/congestion_control/bbr2_simulator_test.cc b/quic/core/congestion_control/bbr2_simulator_test.cc
index 3b08905..9c2cca1 100644
--- a/quic/core/congestion_control/bbr2_simulator_test.cc
+++ b/quic/core/congestion_control/bbr2_simulator_test.cc
@@ -483,6 +483,46 @@
EXPECT_APPROX_EQ(params.RTT(), rtt_stats()->min_rtt(), 0.2f);
}
+TEST_F(Bbr2DefaultTopologyTest, SimpleTransferBBR4) {
+ SetQuicReloadableFlag(quic_bbr2_extra_acked_window, true);
+ SetConnectionOption(kBBR4);
+ 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, SimpleTransferBBR5) {
+ SetQuicReloadableFlag(quic_bbr2_extra_acked_window, true);
+ SetConnectionOption(kBBR5);
+ 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/quic/core/quic_flags_list.h b/quic/core/quic_flags_list.h
index 727f1e2..5773ec5 100644
--- a/quic/core/quic_flags_list.h
+++ b/quic/core/quic_flags_list.h
@@ -135,6 +135,8 @@
QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_bbr2_ignore_inflight_hi_in_probe_up, true)
// When true, the BBQ0 connection option causes QUIC BBR2 to add bytes_acked to probe_up_acked if the connection hasn\'t been app-limited since inflight_hi was utilized.
QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_bbr2_add_bytes_acked_after_inflight_hi_limited, true)
+// When true, the BBR4 copt sets the extra_acked window to 20 RTTs and BBR5 sets it to 40 RTTs.
+QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_bbr2_extra_acked_window, true)
#endif
