In bbr2sender::adjustnetworkparameters, 1) do not inject a bandwidth sample to max bandwidth filter, and 2) update pacing rate after cwnd is updated. protected by --gfe2_reloadable_flag_quic_bbr2_improve_adjust_network_parameters. PiperOrigin-RevId: 321198508 Change-Id: I4366a2b159c48302eaf935784dfb7d093d322257

diff --git a/quic/core/congestion_control/bbr2_misc.cc b/quic/core/congestion_control/bbr2_misc.cc
index cdd0cb5..153f63e 100644
--- a/quic/core/congestion_control/bbr2_misc.cc
+++ b/quic/core/congestion_control/bbr2_misc.cc

@@ -213,7 +213,8 @@
 
 void Bbr2NetworkModel::UpdateNetworkParameters(QuicBandwidth bandwidth,
                                                QuicTime::Delta rtt) {
-  if (!bandwidth.IsInfinite() && bandwidth > MaxBandwidth()) {
+  if (!improve_adjust_network_parameters_ && !bandwidth.IsInfinite() &&
+      bandwidth > MaxBandwidth()) {
     max_bandwidth_filter_.Update(bandwidth);
   }
 

diff --git a/quic/core/congestion_control/bbr2_misc.h b/quic/core/congestion_control/bbr2_misc.h
index cd89e6c..bf22bc5 100644
--- a/quic/core/congestion_control/bbr2_misc.h
+++ b/quic/core/congestion_control/bbr2_misc.h

@@ -446,6 +446,10 @@
   float pacing_gain() const { return pacing_gain_; }
   void set_pacing_gain(float pacing_gain) { pacing_gain_ = pacing_gain; }
 
+  bool improve_adjust_network_parameters() const {
+    return improve_adjust_network_parameters_;
+  }
+
  private:
   const Bbr2Params& Params() const { return *params_; }
   const Bbr2Params* const params_;
@@ -477,6 +481,9 @@
 
   float cwnd_gain_;
   float pacing_gain_;
+
+  const bool improve_adjust_network_parameters_ =
+      GetQuicReloadableFlag(quic_bbr2_improve_adjust_network_parameters);
 };
 
 enum class Bbr2Mode : uint8_t {

diff --git a/quic/core/congestion_control/bbr2_sender.cc b/quic/core/congestion_control/bbr2_sender.cc
index d1b3159..3f80f42 100644
--- a/quic/core/congestion_control/bbr2_sender.cc
+++ b/quic/core/congestion_control/bbr2_sender.cc

@@ -167,14 +167,28 @@
   if (mode_ == Bbr2Mode::STARTUP) {
     const QuicByteCount prior_cwnd = cwnd_;
 
-    // Normally UpdateCongestionWindow updates |cwnd_| towards the target by a
-    // small step per congestion event, by changing |cwnd_| to the bdp at here
-    // we are reducing the number of updates needed to arrive at the target.
-    cwnd_ = model_.BDP(model_.BandwidthEstimate());
-    UpdateCongestionWindow(0);
+    if (model_.improve_adjust_network_parameters()) {
+      QUIC_RELOADABLE_FLAG_COUNT(quic_bbr2_improve_adjust_network_parameters);
+      QuicBandwidth effective_bandwidth =
+          std::max(params.bandwidth, model_.BandwidthEstimate());
+      cwnd_ = cwnd_limits().ApplyLimits(model_.BDP(effective_bandwidth));
+    } else {
+      // Normally UpdateCongestionWindow updates |cwnd_| towards the target by a
+      // small step per congestion event, by changing |cwnd_| to the bdp at here
+      // we are reducing the number of updates needed to arrive at the target.
+      cwnd_ = model_.BDP(model_.BandwidthEstimate());
+      UpdateCongestionWindow(0);
+    }
+
     if (!params.allow_cwnd_to_decrease) {
       cwnd_ = std::max(cwnd_, prior_cwnd);
     }
+
+    if (model_.improve_adjust_network_parameters()) {
+      pacing_rate_ = std::max(
+          pacing_rate_,
+          QuicBandwidth::FromBytesAndTimeDelta(cwnd_, model_.MinRtt()));
+    }
   }
 }
 

diff --git a/quic/core/congestion_control/bbr2_simulator_test.cc b/quic/core/congestion_control/bbr2_simulator_test.cc
index 205d356..8ea5217 100644
--- a/quic/core/congestion_control/bbr2_simulator_test.cc
+++ b/quic/core/congestion_control/bbr2_simulator_test.cc

@@ -331,6 +331,10 @@
 
   QuicConnection* sender_connection() { return sender_endpoint_.connection(); }
 
+  Bbr2Sender::DebugState sender_debug_state() const {
+    return sender_->ExportDebugState();
+  }
+
   const QuicConnectionStats& sender_connection_stats() {
     return sender_connection()->GetStats();
   }
@@ -990,14 +994,46 @@
   EXPECT_FALSE(sender_->BandwidthEstimate().IsZero());
 }
 
+TEST_F(Bbr2DefaultTopologyTest, AdjustNetworkParameters) {
+  DefaultTopologyParams params;
+  CreateNetwork(params);
+
+  QUIC_LOG(INFO) << "Initial cwnd: " << sender_debug_state().congestion_window
+                 << "\nInitial pacing rate: " << sender_->PacingRate(0)
+                 << "\nInitial bandwidth estimate: "
+                 << sender_->BandwidthEstimate()
+                 << "\nInitial rtt: " << sender_debug_state().min_rtt;
+
+  sender_connection()->AdjustNetworkParameters(
+      SendAlgorithmInterface::NetworkParams(params.BottleneckBandwidth(),
+                                            params.RTT(),
+                                            /*allow_cwnd_to_decrease=*/false));
+
+  EXPECT_EQ(params.BDP(), sender_->ExportDebugState().congestion_window);
+
+  if (GetQuicReloadableFlag(quic_bbr2_improve_adjust_network_parameters)) {
+    EXPECT_EQ(params.BottleneckBandwidth(),
+              sender_->PacingRate(/*bytes_in_flight=*/0));
+    EXPECT_NE(params.BottleneckBandwidth(), sender_->BandwidthEstimate());
+  } else {
+    EXPECT_EQ(params.BottleneckBandwidth(), sender_->BandwidthEstimate());
+  }
+
+  EXPECT_APPROX_EQ(params.RTT(), sender_->ExportDebugState().min_rtt, 0.01f);
+
+  DriveOutOfStartup(params);
+}
+
 // All Bbr2MultiSenderTests uses the following network topology:
 //
 //   Sender 0  (A Bbr2Sender)
 //       |
 //       | <-- local_links[0]
 //       |
-//       |  Sender N (1 <= N < kNumLocalLinks) (May or may not be a
-//       Bbr2Sender) |      | |      | <-- local_links[N] |      |
+//       |  Sender N (1 <= N < kNumLocalLinks) (May or may not be a Bbr2Sender)
+//       |      |
+//       |      | <-- local_links[N]
+//       |      |
 //    Network switch
 //           *  <-- the bottleneck queue in the direction
 //           |          of the receiver