relnote: QUIC - Added 'TLPR' connection option to run a finch based

experiment that sets the TailLossProbe delay to 0.5 RTT.

Merge internal change: 101265841

R=rch@chromium.org

Review URL: https://codereview.chromium.org/1310043002

Cr-Commit-Position: refs/heads/master@{#345160}

6 files changed, 52 insertions, 2 deletions

diff --git a/net/quic/crypto/crypto_protocol.h b/net/quic/crypto/crypto_protocol.h
index 607dc25..79e49c9 100644
--- a/net/quic/crypto/crypto_protocol.h
+++ b/net/quic/crypto/crypto_protocol.h
@@ -82,6 +82,8 @@ const QuicTag kTIME = TAG('T', 'I', 'M', 'E');   // Time based loss detection
 const QuicTag kMIN1 = TAG('M', 'I', 'N', '1');   // Min CWND of 1 packet
 const QuicTag kMIN4 = TAG('M', 'I', 'N', '4');   // Min CWND of 4 packets,
                                                  // with a min rate of 1 BDP.
+const QuicTag kTLPR = TAG('T', 'L', 'P', 'R');   // Tail loss probe delay of
+                                                 // 0.5RTT.
 
 // Optional support of truncated Connection IDs.  If sent by a peer, the value
 // is the minimum number of bytes allowed for the connection ID sent to the
diff --git a/net/quic/quic_sent_packet_manager.cc b/net/quic/quic_sent_packet_manager.cc
index aa3423a..da14e4b 100644
--- a/net/quic/quic_sent_packet_manager.cc
+++ b/net/quic/quic_sent_packet_manager.cc
@@ -93,10 +93,10 @@ QuicSentPacketManager::QuicSentPacketManager(
       consecutive_crypto_retransmission_count_(0),
       pending_timer_transmission_count_(0),
       max_tail_loss_probes_(kDefaultMaxTailLossProbes),
+      enable_half_rtt_tail_loss_probe_(false),
       using_pacing_(false),
       use_new_rto_(false),
-      handshake_confirmed_(false) {
-}
+      handshake_confirmed_(false) {}
 
 QuicSentPacketManager::~QuicSentPacketManager() {
 }
@@ -155,6 +155,9 @@ void QuicSentPacketManager::SetFromConfig(const QuicConfig& config) {
   if (config.HasClientSentConnectionOption(kNTLP, perspective_)) {
     max_tail_loss_probes_ = 0;
   }
+  if (config.HasClientSentConnectionOption(kTLPR, perspective_)) {
+    enable_half_rtt_tail_loss_probe_ = true;
+  }
   if (config.HasClientSentConnectionOption(kNRTO, perspective_)) {
     use_new_rto_ = true;
   }
@@ -859,6 +862,11 @@ const QuicTime::Delta QuicSentPacketManager::GetTailLossProbeDelay() const {
   if (srtt.IsZero()) {
     srtt = QuicTime::Delta::FromMicroseconds(rtt_stats_.initial_rtt_us());
   }
+  if (enable_half_rtt_tail_loss_probe_ && consecutive_tlp_count_ == 0u) {
+    return QuicTime::Delta::FromMilliseconds(
+        max(kMinTailLossProbeTimeoutMs,
+            static_cast<int64>(0.5 * srtt.ToMilliseconds())));
+  }
   if (!unacked_packets_.HasMultipleInFlightPackets()) {
     return QuicTime::Delta::Max(
         srtt.Multiply(2), srtt.Multiply(1.5).Add(
diff --git a/net/quic/quic_sent_packet_manager.h b/net/quic/quic_sent_packet_manager.h
index 4b2a59e..336c7ea 100644
--- a/net/quic/quic_sent_packet_manager.h
+++ b/net/quic/quic_sent_packet_manager.h
@@ -386,6 +386,8 @@ class NET_EXPORT_PRIVATE QuicSentPacketManager {
   size_t pending_timer_transmission_count_;
   // Maximum number of tail loss probes to send before firing an RTO.
   size_t max_tail_loss_probes_;
+  // If true, send the TLP at 0.5 RTT.
+  bool enable_half_rtt_tail_loss_probe_;
   bool using_pacing_;
   // If true, use the new RTO with loss based CWND reduction instead of the send
   // algorithms's OnRetransmissionTimeout to reduce the congestion window.
diff --git a/net/quic/quic_sent_packet_manager_test.cc b/net/quic/quic_sent_packet_manager_test.cc
index 51d618a..fe76de0 100644
--- a/net/quic/quic_sent_packet_manager_test.cc
+++ b/net/quic/quic_sent_packet_manager_test.cc
@@ -1553,6 +1553,35 @@ TEST_F(QuicSentPacketManagerTest, NegotiateNoTLPFromOptionsAtClient) {
   EXPECT_EQ(0u, QuicSentPacketManagerPeer::GetMaxTailLossProbes(&manager_));
 }
 
+TEST_F(QuicSentPacketManagerTest, NegotiateTLPRttFromOptionsAtServer) {
+  QuicConfig config;
+  QuicTagVector options;
+
+  options.push_back(kTLPR);
+  QuicConfigPeer::SetReceivedConnectionOptions(&config, options);
+  EXPECT_CALL(*network_change_visitor_, OnCongestionWindowChange());
+  EXPECT_CALL(*network_change_visitor_, OnRttChange());
+  EXPECT_CALL(*send_algorithm_, SetFromConfig(_, _));
+  manager_.SetFromConfig(config);
+  EXPECT_TRUE(
+      QuicSentPacketManagerPeer::GetEnableHalfRttTailLossProbe(&manager_));
+}
+
+TEST_F(QuicSentPacketManagerTest, NegotiateTLPRttFromOptionsAtClient) {
+  QuicConfig client_config;
+  QuicTagVector options;
+
+  options.push_back(kTLPR);
+  QuicSentPacketManagerPeer::SetPerspective(&manager_, Perspective::IS_CLIENT);
+  client_config.SetConnectionOptionsToSend(options);
+  EXPECT_CALL(*network_change_visitor_, OnCongestionWindowChange());
+  EXPECT_CALL(*network_change_visitor_, OnRttChange());
+  EXPECT_CALL(*send_algorithm_, SetFromConfig(_, _));
+  manager_.SetFromConfig(client_config);
+  EXPECT_TRUE(
+      QuicSentPacketManagerPeer::GetEnableHalfRttTailLossProbe(&manager_));
+}
+
 TEST_F(QuicSentPacketManagerTest, NegotiateNewRTOFromOptionsAtServer) {
   EXPECT_FALSE(QuicSentPacketManagerPeer::GetUseNewRto(&manager_));
   QuicConfig config;
diff --git a/net/quic/test_tools/quic_sent_packet_manager_peer.cc b/net/quic/test_tools/quic_sent_packet_manager_peer.cc
index add97bb..ea729fb 100644
--- a/net/quic/test_tools/quic_sent_packet_manager_peer.cc
+++ b/net/quic/test_tools/quic_sent_packet_manager_peer.cc
@@ -26,6 +26,12 @@ void QuicSentPacketManagerPeer::SetMaxTailLossProbes(
 }
 
 // static
+bool QuicSentPacketManagerPeer::GetEnableHalfRttTailLossProbe(
+    QuicSentPacketManager* sent_packet_manager) {
+  return sent_packet_manager->enable_half_rtt_tail_loss_probe_;
+}
+
+// static
 bool QuicSentPacketManagerPeer::GetUseNewRto(
     QuicSentPacketManager* sent_packet_manager) {
   return sent_packet_manager->use_new_rto_;
diff --git a/net/quic/test_tools/quic_sent_packet_manager_peer.h b/net/quic/test_tools/quic_sent_packet_manager_peer.h
index e0686e1..eba5c2e 100644
--- a/net/quic/test_tools/quic_sent_packet_manager_peer.h
+++ b/net/quic/test_tools/quic_sent_packet_manager_peer.h
@@ -22,6 +22,9 @@ class QuicSentPacketManagerPeer {
   static void SetMaxTailLossProbes(
       QuicSentPacketManager* sent_packet_manager, size_t max_tail_loss_probes);
 
+  static bool GetEnableHalfRttTailLossProbe(
+      QuicSentPacketManager* sent_packet_manager);
+
   static bool GetUseNewRto(QuicSentPacketManager* sent_packet_manager);
 
   static QuicByteCount GetReceiveWindow(