From c527fd1d035065a27918e3a9e8a6b57e5f2afbed Mon Sep 17 00:00:00 2001
From: Joseph Beshay <jbeshay@meta.com>
Date: Thu, 23 Jan 2025 17:45:56 -0800
Subject: [PATCH] Add a new option to control bbr2 exiting startup on loss

Summary: As title.

Reviewed By: ritengupta, mjoras

Differential Revision: D68546411

fbshipit-source-id: ae45727fb8443a98e4ac69778d5d85e2512f7a7b
---
 quic/congestion_control/Bbr2.cpp                   | 2 +-
 quic/state/TransportSettings.h                     | 4 ++++
 quic/state/TransportSettingsFunctions.cpp          | 3 ++-
 quic/state/test/TransportSettingsFunctionsTest.cpp | 3 +++
 4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/quic/congestion_control/Bbr2.cpp b/quic/congestion_control/Bbr2.cpp
index e47695fa3..dd41f41ec 100644
--- a/quic/congestion_control/Bbr2.cpp
+++ b/quic/congestion_control/Bbr2.cpp
@@ -466,7 +466,7 @@ void Bbr2CongestionController::checkStartupHighLoss() {
   the same.
   */
   if (fullBwReached_ || !roundStart_ || isAppLimited() ||
-      conn_.transportSettings.ccaConfig.ignoreLoss) {
+      !conn_.transportSettings.ccaConfig.exitStartupOnLoss) {
     // TODO: the appLimited condition means we could tolerate losses in startup
     // if we haven't found the full bandwidth. This may need to be revisited.
 
diff --git a/quic/state/TransportSettings.h b/quic/state/TransportSettings.h
index 8d226db21..cc9433221 100644
--- a/quic/state/TransportSettings.h
+++ b/quic/state/TransportSettings.h
@@ -76,6 +76,10 @@ struct CongestionControlConfig {
   // Whether BBR2 should ignore packet loss (i.e. act more like BBR1)
   bool ignoreLoss{false};
 
+  // Used by: BBR2
+  // Whether BBR2 should check packet loss to exit startup
+  bool exitStartupOnLoss{true};
+
   // Used by: BBR2
   // Whether BBR2 should enable reno coexistence.
   bool enableRenoCoexistence{false};
diff --git a/quic/state/TransportSettingsFunctions.cpp b/quic/state/TransportSettingsFunctions.cpp
index f969672dc..5ee1b952b 100644
--- a/quic/state/TransportSettingsFunctions.cpp
+++ b/quic/state/TransportSettingsFunctions.cpp
@@ -64,7 +64,7 @@ quic::CongestionControlConfig parseCongestionControlConfig(
   quic::CongestionControlConfig ccaConfig;
 
   // Parse known boolean fields
-  const std::array<std::pair<std::string_view, bool&>, 12> boolFields = {
+  const std::array<std::pair<std::string_view, bool&>, 13> boolFields = {
       {{"conservativeRecovery", ccaConfig.conservativeRecovery},
        {"largeProbeRttCwnd", ccaConfig.largeProbeRttCwnd},
        {"enableAckAggregationInStartup",
@@ -76,6 +76,7 @@ quic::CongestionControlConfig parseCongestionControlConfig(
        {"leaveHeadroomForCwndLimited", ccaConfig.leaveHeadroomForCwndLimited},
        {"ignoreInflightHi", ccaConfig.ignoreInflightHi},
        {"ignoreLoss", ccaConfig.ignoreLoss},
+       {"exitStartupOnLoss", ccaConfig.exitStartupOnLoss},
        {"enableRenoCoexistence", ccaConfig.enableRenoCoexistence},
        {"paceInitCwnd", ccaConfig.paceInitCwnd}}};
 
diff --git a/quic/state/test/TransportSettingsFunctionsTest.cpp b/quic/state/test/TransportSettingsFunctionsTest.cpp
index d0239290b..401f474ac 100644
--- a/quic/state/test/TransportSettingsFunctionsTest.cpp
+++ b/quic/state/test/TransportSettingsFunctionsTest.cpp
@@ -66,6 +66,7 @@ TEST_F(TransportSettingsFunctionsTest, FullConfig) {
       "},"
       "\"ignoreInflightHi\": true, "
       "\"ignoreLoss\": true, "
+      "\"exitStartupOnLoss\": false, "
       "\"enableRenoCoexistence\": true, "
       "\"paceInitCwnd\": false, "
       "\"overrideCruisePacingGain\": 7.9, "
@@ -83,6 +84,7 @@ TEST_F(TransportSettingsFunctionsTest, FullConfig) {
   EXPECT_EQ(config.leaveHeadroomForCwndLimited, true);
   EXPECT_EQ(config.ignoreInflightHi, true);
   EXPECT_EQ(config.ignoreLoss, true);
+  EXPECT_EQ(config.exitStartupOnLoss, false);
   EXPECT_EQ(config.enableRenoCoexistence, true);
   EXPECT_EQ(config.paceInitCwnd, false);
   EXPECT_EQ(config.overrideCruisePacingGain, 7.9f);
@@ -112,6 +114,7 @@ TEST_F(TransportSettingsFunctionsTest, UnspecifiedFieldsAreDefaulted) {
   EXPECT_EQ(config.drainToTarget, false);
   EXPECT_EQ(config.ignoreInflightHi, false);
   EXPECT_EQ(config.ignoreLoss, false);
+  EXPECT_EQ(config.exitStartupOnLoss, true);
   EXPECT_EQ(config.enableRenoCoexistence, false);
   EXPECT_EQ(config.overrideCruisePacingGain, -1.0f);
   EXPECT_EQ(config.overrideCruiseCwndGain, -1.0f);