Implement congestion window direct pushback to encoders. (Without TaskQueue)

Bug: None
Change-Id: I3c6da916ce5f4a32ff47bfb0894b00f11fbf7823
Reviewed-on: https://webrtc-review.googlesource.com/86605
Commit-Queue: Ying Wang <yinwa@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24008}

modules/congestion_controller/BUILD.gn

@@ -20,6 +20,8 @@ rtc_static_library("congestion_controller") {
   visibility = [ "*" ]
   configs += [ ":bwe_test_logging" ]
   sources = [
+    "congestion_window_pushback_controller.cc",
+    "congestion_window_pushback_controller.h",
     "include/network_changed_observer.h",
     "include/receive_side_congestion_controller.h",
     "include/send_side_congestion_controller.h",
@@ -37,7 +39,9 @@ rtc_static_library("congestion_controller") {
     ":transport_feedback",
     "..:module_api",
     "../..:webrtc_common",
+    "../../api/transport:network_control",
     "../../rtc_base:checks",
+    "../../rtc_base:ptr_util",
     "../../rtc_base:rate_limiter",
     "../../system_wrappers",
     "../../system_wrappers:field_trial_api",
@@ -95,6 +99,7 @@ if (rtc_include_tests) {
     testonly = true
 
     sources = [
+      "congestion_window_pushback_controller_unittest.cc",
       "receive_side_congestion_controller_unittest.cc",
       "send_side_congestion_controller_unittest.cc",
       "transport_feedback_adapter_unittest.cc",

modules/congestion_controller/congestion_window_pushback_controller.cc

@@ -0,0 +1,93 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <string>
+#include <algorithm>
+
+#include "modules/congestion_controller/congestion_window_pushback_controller.h"
+#include "system_wrappers/include/field_trial.h"
+
+namespace webrtc {
+
+// When CongestionWindowPushback is enabled, the pacer is oblivious to
+// the congestion window. The relation between outstanding data and
+// the congestion window affects encoder allocations directly.
+// This experiment is build on top of congestion window experiment.
+const char kCongestionPushbackExperiment[] = "WebRTC-CongestionWindowPushback";
+const uint32_t kDefaultMinPushbackTargetBitrateBps = 30000;
+
+bool ReadCongestionWindowPushbackExperimentParameter(
+    uint32_t* min_pushback_target_bitrate_bps) {
+  RTC_DCHECK(min_pushback_target_bitrate_bps);
+  std::string experiment_string =
+      webrtc::field_trial::FindFullName(kCongestionPushbackExperiment);
+  int parsed_values = sscanf(experiment_string.c_str(), "Enabled-%" PRIu32,
+                             min_pushback_target_bitrate_bps);
+  if (parsed_values == 1) {
+    RTC_CHECK_GE(*min_pushback_target_bitrate_bps, 0)
+        << "Min pushback target bitrate must be greater than or equal to 0.";
+    return true;
+  }
+  return false;
+}
+
+CongestionWindowPushbackController::CongestionWindowPushbackController() {
+  if (!ReadCongestionWindowPushbackExperimentParameter(
+          &min_pushback_target_bitrate_bps_)) {
+    min_pushback_target_bitrate_bps_ = kDefaultMinPushbackTargetBitrateBps;
+  }
+}
+
+void CongestionWindowPushbackController::UpdateOutstandingData(
+    size_t outstanding_bytes) {
+  outstanding_bytes_ = outstanding_bytes;
+}
+
+void CongestionWindowPushbackController::UpdateMaxOutstandingData(
+    size_t max_outstanding_bytes) {
+  DataSize data_window = DataSize::bytes(max_outstanding_bytes);
+  if (current_data_window_) {
+    data_window = (data_window + current_data_window_.value()) / 2;
+  }
+  current_data_window_ = data_window;
+}
+
+void CongestionWindowPushbackController::SetDataWindow(DataSize data_window) {
+  current_data_window_ = data_window;
+}
+
+uint32_t CongestionWindowPushbackController::UpdateTargetBitrate(
+    uint32_t bitrate_bps) {
+  if (!current_data_window_ || current_data_window_->IsZero())
+    return bitrate_bps;
+  double fill_ratio =
+      outstanding_bytes_ / static_cast<double>(current_data_window_->bytes());
+  if (fill_ratio > 1.5) {
+    encoding_rate_ratio_ *= 0.9;
+  } else if (fill_ratio > 1) {
+    encoding_rate_ratio_ *= 0.95;
+  } else if (fill_ratio < 0.1) {
+    encoding_rate_ratio_ = 1.0;
+  } else {
+    encoding_rate_ratio_ *= 1.05;
+    encoding_rate_ratio_ = std::min(encoding_rate_ratio_, 1.0);
+  }
+  uint32_t adjusted_target_bitrate_bps =
+      static_cast<uint32_t>(bitrate_bps * encoding_rate_ratio_);
+
+  // Do not adjust below the minimum pushback bitrate but do obey if the
+  // original estimate is below it.
+  bitrate_bps = adjusted_target_bitrate_bps < min_pushback_target_bitrate_bps_
+                    ? std::min(bitrate_bps, min_pushback_target_bitrate_bps_)
+                    : adjusted_target_bitrate_bps;
+  return bitrate_bps;
+}
+
+}  // namespace webrtc

modules/congestion_controller/congestion_window_pushback_controller.h

@@ -0,0 +1,43 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef MODULES_CONGESTION_CONTROLLER_CONGESTION_WINDOW_PUSHBACK_CONTROLLER_H_
+#define MODULES_CONGESTION_CONTROLLER_CONGESTION_WINDOW_PUSHBACK_CONTROLLER_H_
+
+#include "api/transport/network_types.h"
+#include "common_types.h"  // NOLINT(build/include)
+#include "rtc_base/criticalsection.h"
+#include "rtc_base/format_macros.h"
+
+namespace webrtc {
+
+// This class enables pushback from congestion window directly to video encoder.
+// When the congestion window is filling up, the video encoder target bitrate
+// will be reduced accordingly to accommodate the network changes. To avoid
+// pausing video too frequently, a minimum encoder target bitrate threshold is
+// used to prevent video pause due to a full congestion window.
+class CongestionWindowPushbackController {
+ public:
+  CongestionWindowPushbackController();
+  void UpdateOutstandingData(size_t outstanding_bytes);
+  void UpdateMaxOutstandingData(size_t max_outstanding_bytes);
+  uint32_t UpdateTargetBitrate(uint32_t bitrate_bps);
+  void SetDataWindow(DataSize data_window);
+
+ private:
+  absl::optional<DataSize> current_data_window_;
+  size_t outstanding_bytes_ = 0;
+  uint32_t min_pushback_target_bitrate_bps_;
+  double encoding_rate_ratio_ = 1.0;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_CONGESTION_CONTROLLER_CONGESTION_WINDOW_PUSHBACK_CONTROLLER_H_

modules/congestion_controller/congestion_window_pushback_controller_unittest.cc

@@ -0,0 +1,65 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "modules/congestion_controller/congestion_window_pushback_controller.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
+
+using testing::_;
+
+namespace webrtc {
+namespace test {
+
+class CongestionWindowPushbackControllerTest : public ::testing::Test {
+ protected:
+  CongestionWindowPushbackController cwnd_controller_;
+};
+
+TEST_F(CongestionWindowPushbackControllerTest, FullCongestionWindow) {
+  cwnd_controller_.UpdateOutstandingData(100000);
+  cwnd_controller_.UpdateMaxOutstandingData(50000);
+
+  uint32_t bitrate_bps = 80000;
+  bitrate_bps = cwnd_controller_.UpdateTargetBitrate(bitrate_bps);
+  EXPECT_EQ(72000u, bitrate_bps);
+
+  cwnd_controller_.UpdateMaxOutstandingData(50000);
+  bitrate_bps = cwnd_controller_.UpdateTargetBitrate(bitrate_bps);
+  EXPECT_EQ(static_cast<uint32_t>(72000 * 0.9 * 0.9), bitrate_bps);
+}
+
+TEST_F(CongestionWindowPushbackControllerTest, NormalCongestionWindow) {
+  cwnd_controller_.UpdateOutstandingData(100000);
+  cwnd_controller_.SetDataWindow(DataSize::bytes(200000));
+
+  uint32_t bitrate_bps = 80000;
+  bitrate_bps = cwnd_controller_.UpdateTargetBitrate(bitrate_bps);
+  EXPECT_EQ(80000u, bitrate_bps);
+
+  cwnd_controller_.UpdateMaxOutstandingData(20000);
+  bitrate_bps = cwnd_controller_.UpdateTargetBitrate(bitrate_bps);
+  EXPECT_EQ(80000u, bitrate_bps);
+}
+
+TEST_F(CongestionWindowPushbackControllerTest, LowBitrate) {
+  cwnd_controller_.UpdateOutstandingData(100000);
+  cwnd_controller_.SetDataWindow(DataSize::bytes(50000));
+
+  uint32_t bitrate_bps = 35000;
+  bitrate_bps = cwnd_controller_.UpdateTargetBitrate(bitrate_bps);
+  EXPECT_EQ(static_cast<uint32_t>(35000 * 0.9), bitrate_bps);
+
+  cwnd_controller_.UpdateMaxOutstandingData(20000);
+  bitrate_bps = cwnd_controller_.UpdateTargetBitrate(bitrate_bps);
+  EXPECT_EQ(30000u, bitrate_bps);
+}
+
+}  // namespace test
+}  // namespace webrtc

modules/congestion_controller/include/send_side_congestion_controller.h

@@ -39,6 +39,7 @@ class AcknowledgedBitrateEstimator;
 class ProbeController;
 class RateLimiter;
 class RtcEventLog;
+class CongestionWindowPushbackController;
 
 class SendSideCongestionController
     : public SendSideCongestionControllerInterface {
@@ -169,6 +170,9 @@ class SendSideCongestionController
   bool pacer_pushback_experiment_ = false;
   float encoding_rate_ = 1.0;
 
+  const std::unique_ptr<CongestionWindowPushbackController>
+      congestion_window_pushback_controller_;
+
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(SendSideCongestionController);
 };
 

modules/congestion_controller/rtp/send_side_congestion_controller.cc

@@ -16,6 +16,7 @@
 #include <vector>
 #include "absl/memory/memory.h"
 #include "api/transport/network_types.h"
+#include "modules/congestion_controller/congestion_window_pushback_controller.h"
 #include "modules/congestion_controller/goog_cc/include/goog_cc_factory.h"
 #include "modules/remote_bitrate_estimator/include/bwe_defines.h"
 #include "rtc_base/bind.h"
@@ -38,6 +39,8 @@ namespace webrtc_cc {
 namespace {
 using send_side_cc_internal::PeriodicTask;
 
+const char kCwndExperiment[] = "WebRTC-CwndExperiment";
+
 // When CongestionWindowPushback is enabled, the pacer is oblivious to
 // the congestion window. The relation between outstanding data and
 // the congestion window affects encoder allocations directly.
@@ -47,22 +50,6 @@ const char kCongestionPushbackExperiment[] = "WebRTC-CongestionWindowPushback";
 // the congestion window and/or data spikes reduces encoder allocations.
 const char kPacerPushbackExperiment[] = "WebRTC-PacerPushbackExperiment";
 const int64_t PacerQueueUpdateIntervalMs = 25;
-const uint32_t kDefaultMinPushbackTargetBitrateBps = 30000;
-
-bool ReadCongestionWindowPushbackExperimentParameter(
-    uint32_t* min_pushback_target_bitrate_bps) {
-  RTC_DCHECK(min_pushback_target_bitrate_bps);
-  std::string experiment_string =
-      webrtc::field_trial::FindFullName(kCongestionPushbackExperiment);
-  int parsed_values = sscanf(experiment_string.c_str(), "Enabled-%" PRIu32,
-                             min_pushback_target_bitrate_bps);
-  if (parsed_values == 1) {
-    RTC_CHECK_GE(*min_pushback_target_bitrate_bps, 0)
-        << "Min pushback target bitrate must be greater than or equal to 0.";
-    return true;
-  }
-  return false;
-}
 
 bool IsPacerPushbackExperimentEnabled() {
   return webrtc::field_trial::IsEnabled(kPacerPushbackExperiment) ||
@@ -71,8 +58,16 @@ bool IsPacerPushbackExperimentEnabled() {
               webrtc::runtime_enabled_features::kDualStreamModeFeatureName));
 }
 
-bool IsCongestionWindowExperimentEnabled() {
-  return webrtc::field_trial::IsEnabled(kCongestionPushbackExperiment);
+bool IsCongestionWindowPushbackExperimentEnabled() {
+  return webrtc::field_trial::IsEnabled(kCongestionPushbackExperiment) &&
+         webrtc::field_trial::IsEnabled(kCwndExperiment);
+}
+
+std::unique_ptr<CongestionWindowPushbackController>
+MaybeInitalizeCongestionWindowPushbackController() {
+  return IsCongestionWindowPushbackExperimentEnabled()
+             ? absl::make_unique<CongestionWindowPushbackController>()
+             : nullptr;
 }
 
 void SortPacketFeedbackVector(std::vector<webrtc::PacketFeedback>* input) {
@@ -200,17 +195,16 @@ class ControlHandler {
   PacerController* pacer_controller_;
 
   absl::optional<TargetTransferRate> current_target_rate_msg_;
-  absl::optional<DataSize> congestion_window_;
-  DataSize outstanding_data_ = DataSize::Zero();
   bool network_available_ = true;
   int64_t last_reported_target_bitrate_bps_ = 0;
   uint8_t last_reported_fraction_loss_ = 0;
   int64_t last_reported_rtt_ms_ = 0;
   const bool pacer_pushback_experiment_ = false;
-  const bool congestion_window_pushback_experiment_ = false;
   uint32_t min_pushback_target_bitrate_bps_;
   int64_t pacer_expected_queue_ms_ = 0;
   double encoding_rate_ratio_ = 1.0;
+  const std::unique_ptr<CongestionWindowPushbackController>
+      congestion_window_pushback_controller_;
 
   rtc::SequencedTaskChecker sequenced_checker_;
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(ControlHandler);
@@ -222,21 +216,18 @@ ControlHandler::ControlHandler(NetworkChangedObserver* observer,
     : observer_(observer),
       pacer_controller_(pacer_controller),
       pacer_pushback_experiment_(IsPacerPushbackExperimentEnabled()),
-      congestion_window_pushback_experiment_(
-          IsCongestionWindowExperimentEnabled()) {
+      congestion_window_pushback_controller_(
+          MaybeInitalizeCongestionWindowPushbackController()) {
   sequenced_checker_.Detach();
-  if (congestion_window_pushback_experiment_ &&
-      !ReadCongestionWindowPushbackExperimentParameter(
-          &min_pushback_target_bitrate_bps_)) {
-    min_pushback_target_bitrate_bps_ = kDefaultMinPushbackTargetBitrateBps;
-  }
 }
 
 void ControlHandler::PostUpdates(NetworkControlUpdate update) {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&sequenced_checker_);
   if (update.congestion_window) {
-    congestion_window_ = update.congestion_window;
-    if (!congestion_window_pushback_experiment_) {
+    if (congestion_window_pushback_controller_) {
+      congestion_window_pushback_controller_->SetDataWindow(
+          update.congestion_window.value());
+    } else {
       pacer_controller_->OnCongestionWindow(*update.congestion_window);
     }
   }
@@ -260,7 +251,10 @@ void ControlHandler::OnNetworkAvailability(NetworkAvailability msg) {
 
 void ControlHandler::OnOutstandingData(DataSize in_flight_data) {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&sequenced_checker_);
-  outstanding_data_ = in_flight_data;
+  if (congestion_window_pushback_controller_) {
+    congestion_window_pushback_controller_->UpdateOutstandingData(
+        in_flight_data.bytes());
+  }
   OnNetworkInvalidation();
 }
 
@@ -289,29 +283,10 @@ void ControlHandler::OnNetworkInvalidation() {
 
   if (!network_available_) {
     target_bitrate_bps = 0;
-  } else if (congestion_window_pushback_experiment_ && congestion_window_) {
-    double fill_ratio = outstanding_data_.bytes() /
-                        static_cast<double>(congestion_window_->bytes());
-    if (fill_ratio > 1.5) {
-      encoding_rate_ratio_ *= 0.9;
-    } else if (fill_ratio > 1) {
-      encoding_rate_ratio_ *= 0.95;
-    } else if (fill_ratio < 0.1) {
-      encoding_rate_ratio_ = 1.0;
-    } else {
-      encoding_rate_ratio_ *= 1.05;
-      encoding_rate_ratio_ = std::min(encoding_rate_ratio_, 1.0);
-    }
-
-    uint32_t adjusted_target_bitrate_bps =
-        static_cast<uint32_t>(target_bitrate_bps * encoding_rate_ratio_);
-
-    // If adjusted target bitrate is lower than minimum target bitrate,
-    // does not reduce target bitrate lower than minimum target bitrate.
+  } else if (congestion_window_pushback_controller_) {
     target_bitrate_bps =
-        adjusted_target_bitrate_bps < min_pushback_target_bitrate_bps_
-            ? std::min(target_bitrate_bps, min_pushback_target_bitrate_bps_)
-            : adjusted_target_bitrate_bps;
+        congestion_window_pushback_controller_->UpdateTargetBitrate(
+            target_bitrate_bps);
   } else if (!pacer_pushback_experiment_) {
     target_bitrate_bps = IsSendQueueFull() ? 0 : target_bitrate_bps;
   } else {

modules/congestion_controller/send_side_congestion_controller.cc

@@ -18,6 +18,7 @@
 
 #include "absl/memory/memory.h"
 #include "modules/bitrate_controller/include/bitrate_controller.h"
+#include "modules/congestion_controller/congestion_window_pushback_controller.h"
 #include "modules/congestion_controller/goog_cc/acknowledged_bitrate_estimator.h"
 #include "modules/congestion_controller/goog_cc/probe_controller.h"
 #include "modules/remote_bitrate_estimator/include/bwe_defines.h"
@@ -36,6 +37,12 @@ namespace {
 
 const char kCwndExperiment[] = "WebRTC-CwndExperiment";
 const char kPacerPushbackExperiment[] = "WebRTC-PacerPushbackExperiment";
+
+// When CongestionWindowPushback is enabled, the pacer is oblivious to
+// the congestion window. The relation between outstanding data and
+// the congestion window affects encoder allocations directly.
+const char kCongestionPushbackExperiment[] = "WebRTC-CongestionWindowPushback";
+
 const int64_t kDefaultAcceptedQueueMs = 250;
 
 bool CwndExperimentEnabled() {
@@ -59,6 +66,18 @@ bool ReadCwndExperimentParameter(int64_t* accepted_queue_ms) {
   return false;
 }
 
+bool IsCongestionWindowPushbackExperimentEnabled() {
+  return webrtc::field_trial::IsEnabled(kCongestionPushbackExperiment) &&
+         webrtc::field_trial::IsEnabled(kCwndExperiment);
+}
+
+std::unique_ptr<CongestionWindowPushbackController>
+MaybeCreateCongestionWindowPushbackController() {
+  return IsCongestionWindowPushbackExperimentEnabled()
+             ? absl::make_unique<CongestionWindowPushbackController>()
+             : nullptr;
+}
+
 static const int64_t kRetransmitWindowSizeMs = 500;
 
 // Makes sure that the bitrate and the min, max values are in valid range.
@@ -135,7 +154,9 @@ SendSideCongestionController::SendSideCongestionController(
       send_side_bwe_with_overhead_(
           webrtc::field_trial::IsEnabled("WebRTC-SendSideBwe-WithOverhead")),
       transport_overhead_bytes_per_packet_(0),
-      pacer_pushback_experiment_(IsPacerPushbackExperimentEnabled()) {
+      pacer_pushback_experiment_(IsPacerPushbackExperimentEnabled()),
+      congestion_window_pushback_controller_(
+          MaybeCreateCongestionWindowPushbackController()) {
   delay_based_bwe_->SetMinBitrate(min_bitrate_bps_);
   if (in_cwnd_experiment_ &&
       !ReadCwndExperimentParameter(&accepted_queue_ms_)) {
@@ -418,9 +439,10 @@ void SendSideCongestionController::OnTransportFeedback(
         pacer_->GetApplicationLimitedRegionStartTime());
     probe_controller_->RequestProbe(clock_->TimeInMilliseconds());
   }
-  if (in_cwnd_experiment_)
+  if (in_cwnd_experiment_) {
     LimitOutstandingBytes(transport_feedback_adapter_.GetOutstandingBytes());
   }
+}
 
 void SendSideCongestionController::LimitOutstandingBytes(
     size_t num_outstanding_bytes) {
@@ -443,8 +465,15 @@ void SendSideCongestionController::LimitOutstandingBytes(
                    << " max outstanding: " << max_outstanding_bytes;
   RTC_LOG(LS_INFO) << "Feedback rtt: " << *min_rtt_ms
                    << " Bitrate: " << last_reported_bitrate_bps_;
+  if (congestion_window_pushback_controller_) {
+    congestion_window_pushback_controller_->UpdateOutstandingData(
+        num_outstanding_bytes);
+    congestion_window_pushback_controller_->UpdateMaxOutstandingData(
+        max_outstanding_bytes);
+  } else {
     pause_pacer_ = num_outstanding_bytes > max_outstanding_bytes;
   }
+}
 
 std::vector<PacketFeedback>
 SendSideCongestionController::GetTransportFeedbackVector() const {
@@ -478,11 +507,14 @@ void SendSideCongestionController::MaybeTriggerOnNetworkChanged() {
     retransmission_rate_limiter_->SetMaxRate(bitrate_bps);
   }
 
-  if (!pacer_pushback_experiment_) {
-    bitrate_bps = IsNetworkDown() || IsSendQueueFull() ? 0 : bitrate_bps;
-  } else {
   if (IsNetworkDown()) {
     bitrate_bps = 0;
+  } else if (congestion_window_pushback_controller_) {
+    rtc::CritScope lock(&network_state_lock_);
+    bitrate_bps = congestion_window_pushback_controller_->UpdateTargetBitrate(
+        bitrate_bps);
+  } else if (!pacer_pushback_experiment_) {
+    bitrate_bps = IsSendQueueFull() ? 0 : bitrate_bps;
   } else {
     int64_t queue_length_ms = pacer_->ExpectedQueueTimeMs();
 
@@ -497,7 +529,6 @@ void SendSideCongestionController::MaybeTriggerOnNetworkChanged() {
     bitrate_bps *= encoding_rate_;
     bitrate_bps = bitrate_bps < 50000 ? 0 : bitrate_bps;
   }
-  }
 
   if (HasNetworkParametersToReportChanged(bitrate_bps, fraction_loss, rtt)) {
     int64_t probing_interval_ms;