Continue sending at the max bandwidth measured in the last two rounds for another SRTT. Protected …

net/quic/core/congestion_control/bbr_sender_test.cc

Index: net/quic/core/congestion_control/bbr_sender_test.cc
diff --git a/net/quic/core/congestion_control/bbr_sender_test.cc b/net/quic/core/congestion_control/bbr_sender_test.cc
index b0813e059dfd7afedf6713c8ac289d3c6bac4b33..86c30a908061d96713115e3444e53768205cef9d 100644
--- a/net/quic/core/congestion_control/bbr_sender_test.cc
+++ b/net/quic/core/congestion_control/bbr_sender_test.cc
@@ -343,6 +343,34 @@ TEST_F(BbrSenderTest, SimpleTransfer2RTTAggregationBytes) {
   ExpectApproxEq(kTestRtt, rtt_stats_->min_rtt(), 0.1f);
 }
 
+TEST_F(BbrSenderTest, SimpleTransfer2RTTAggregationKeepSending) {
+  FLAGS_quic_reloadable_flag_quic_bbr_ack_spacing2 = false;
+  FLAGS_quic_reloadable_flag_quic_bbr_ack_aggregation_bytes = false;
+  FLAGS_quic_reloadable_flag_quic_bbr_add_tso_cwnd = false;
+  FLAGS_quic_reloadable_flag_quic_bbr_keep_sending_at_recent_rate = true;
+  CreateDefaultSetup();
+  // 2 RTTs of aggregation, with a max of 10kb.
+  EnableAggregation(10 * 1024, 2 * kTestRtt);
+
+  // Transfer 12MB.
+  DoSimpleTransfer(12 * 1024 * 1024, QuicTime::Delta::FromSeconds(35));
+  EXPECT_EQ(BbrSender::PROBE_BW, sender_->ExportDebugState().mode);
+  // It's possible to read a bandwidth as much as 50% too high with aggregation.
+  EXPECT_LE(kTestLinkBandwidth * 0.99f,
+            sender_->ExportDebugState().max_bandwidth);
+  // TODO(ianswett): Tighten this bound once we understand why BBR is
+  // overestimating bandwidth with aggregation. b/36022633
+  EXPECT_GE(kTestLinkBandwidth * 1.5f,
+            sender_->ExportDebugState().max_bandwidth);
+  // TODO(ianswett): Expect 0 packets are lost once BBR no longer measures
+  // bandwidth higher than the link rate.
+  EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
+  // The margin here is high, because the aggregation greatly increases
+  // smoothed rtt.
+  EXPECT_GE(kTestRtt * 4, rtt_stats_->smoothed_rtt());
+  ExpectApproxEq(kTestRtt, rtt_stats_->min_rtt(), 0.1f);
+}
+
 // Test a simple long data transfer with 2 rtts of aggregation.
 TEST_F(BbrSenderTest, SimpleTransferAckDecimation) {
   FLAGS_quic_reloadable_flag_quic_bbr_ack_spacing2 = false;
@@ -380,6 +408,43 @@ TEST_F(BbrSenderTest, SimpleTransferAckDecimation) {
   ExpectApproxEq(kTestRtt, rtt_stats_->min_rtt(), 0.1f);
 }
 
+TEST_F(BbrSenderTest, SimpleTransferAckDecimationKeepSending) {
+  FLAGS_quic_reloadable_flag_quic_bbr_ack_spacing2 = false;
+  FLAGS_quic_reloadable_flag_quic_bbr_ack_aggregation_bytes = false;
+  FLAGS_quic_reloadable_flag_quic_bbr_keep_sending_at_recent_rate = true;
+  // Decrease the CWND gain so extra CWND is required with stretch acks.
+  base::SetFlag(&FLAGS_quic_bbr_cwnd_gain, 1.0);
+  sender_ = new BbrSender(
+      rtt_stats_,
+      QuicSentPacketManagerPeer::GetUnackedPacketMap(
+          QuicConnectionPeer::GetSentPacketManager(bbr_sender_.connection())),
+      kInitialCongestionWindowPackets, kDefaultMaxCongestionWindowPackets,
+      &random_);
+  QuicConnectionPeer::SetSendAlgorithm(bbr_sender_.connection(), sender_);
+  // Enable Ack Decimation on the receiver.
+  QuicConnectionPeer::SetAckMode(receiver_.connection(),
+                                 QuicConnection::AckMode::ACK_DECIMATION);
+  CreateDefaultSetup();
+
+  // Transfer 12MB.
+  DoSimpleTransfer(12 * 1024 * 1024, QuicTime::Delta::FromSeconds(35));
+  EXPECT_EQ(BbrSender::PROBE_BW, sender_->ExportDebugState().mode);
+  // It's possible to read a bandwidth as much as 50% too high with aggregation.
+  EXPECT_LE(kTestLinkBandwidth * 0.99f,
+            sender_->ExportDebugState().max_bandwidth);
+  // TODO(ianswett): Tighten this bound once we understand why BBR is
+  // overestimating bandwidth with aggregation. b/36022633
+  EXPECT_GE(kTestLinkBandwidth * 1.5f,
+            sender_->ExportDebugState().max_bandwidth);
+  // TODO(ianswett): Expect 0 packets are lost once BBR no longer measures
+  // bandwidth higher than the link rate.
+  EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
+  // The margin here is high, because the aggregation greatly increases
+  // smoothed rtt.
+  EXPECT_GE(kTestRtt * 2, rtt_stats_->smoothed_rtt());
+  ExpectApproxEq(kTestRtt, rtt_stats_->min_rtt(), 0.1f);
+}
+
 // Test the number of losses incurred by the startup phase in a situation when
 // the buffer is less than BDP.
 TEST_F(BbrSenderTest, PacketLossOnSmallBufferStartup) {