Adds utility function for PCC.

Bug: webrtc:9434
Change-Id: I840f39afdff1851d939005f82e64b23927bf455e
Reviewed-on: https://webrtc-review.googlesource.com/87146
Commit-Queue: Anastasia Koloskova <koloskova@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24369}

modules/congestion_controller/pcc/BUILD.gn

@@ -30,16 +30,30 @@ rtc_static_library("rtt_tracker") {
   ]
 }
 
+rtc_static_library("utility_function") {
+  sources = [
+    "utility_function.cc",
+    "utility_function.h",
+  ]
+  deps = [
+    ":monitor_interval",
+    "../../../api/transport:network_control",
+    "../../../rtc_base:rtc_base_approved",
+  ]
+}
+
 if (rtc_include_tests) {
   rtc_source_set("pcc_unittests") {
     testonly = true
     sources = [
       "monitor_interval_unittest.cc",
       "rtt_tracker_unittest.cc",
+      "utility_function_unittest.cc",
     ]
     deps = [
       ":monitor_interval",
       ":rtt_tracker",
+      ":utility_function",
       "../../../api/transport:network_control_test",
       "../../../api/units:data_rate",
       "../../../api/units:time_delta",

modules/congestion_controller/pcc/utility_function.cc

@@ -0,0 +1,84 @@
+/*
+ *  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/pcc/utility_function.h"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+namespace webrtc {
+namespace pcc {
+
+VivaceUtilityFunction::VivaceUtilityFunction(
+    double delay_gradient_coefficient,
+    double loss_coefficient,
+    double throughput_coefficient,
+    double throughput_power,
+    double delay_gradient_threshold,
+    double delay_gradient_negative_bound)
+    : delay_gradient_coefficient_(delay_gradient_coefficient),
+      loss_coefficient_(loss_coefficient),
+      throughput_power_(throughput_power),
+      throughput_coefficient_(throughput_coefficient),
+      delay_gradient_threshold_(delay_gradient_threshold),
+      delay_gradient_negative_bound_(delay_gradient_negative_bound) {
+  RTC_DCHECK_GE(delay_gradient_negative_bound_, 0);
+}
+
+double VivaceUtilityFunction::Compute(
+    const PccMonitorInterval& monitor_interval) const {
+  RTC_DCHECK(monitor_interval.IsFeedbackCollectionDone());
+  double bitrate = monitor_interval.GetTargetSendingRate().bps();
+  double loss_rate = monitor_interval.GetLossRate();
+  double rtt_gradient =
+      monitor_interval.ComputeDelayGradient(delay_gradient_threshold_);
+  rtt_gradient = std::max(rtt_gradient, -delay_gradient_negative_bound_);
+  return (throughput_coefficient_ * std::pow(bitrate, throughput_power_)) -
+         (delay_gradient_coefficient_ * bitrate * rtt_gradient) -
+         (loss_coefficient_ * bitrate * loss_rate);
+}
+
+VivaceUtilityFunction::~VivaceUtilityFunction() = default;
+
+ModifiedVivaceUtilityFunction::ModifiedVivaceUtilityFunction(
+    double delay_gradient_coefficient,
+    double loss_coefficient,
+    double throughput_coefficient,
+    double throughput_power,
+    double delay_gradient_threshold,
+    double delay_gradient_negative_bound)
+    : delay_gradient_coefficient_(delay_gradient_coefficient),
+      loss_coefficient_(loss_coefficient),
+      throughput_power_(throughput_power),
+      throughput_coefficient_(throughput_coefficient),
+      delay_gradient_threshold_(delay_gradient_threshold),
+      delay_gradient_negative_bound_(delay_gradient_negative_bound) {
+  RTC_DCHECK_GE(delay_gradient_negative_bound_, 0);
+}
+
+double ModifiedVivaceUtilityFunction::Compute(
+    const PccMonitorInterval& monitor_interval) const {
+  RTC_DCHECK(monitor_interval.IsFeedbackCollectionDone());
+  double bitrate = monitor_interval.GetTargetSendingRate().bps();
+  double loss_rate = monitor_interval.GetLossRate();
+  double rtt_gradient =
+      monitor_interval.ComputeDelayGradient(delay_gradient_threshold_);
+  rtt_gradient = std::max(rtt_gradient, -delay_gradient_negative_bound_);
+  return (throughput_coefficient_ * std::pow(bitrate, throughput_power_) *
+          bitrate) -
+         (delay_gradient_coefficient_ * bitrate * bitrate * rtt_gradient) -
+         (loss_coefficient_ * bitrate * bitrate * loss_rate);
+}
+
+ModifiedVivaceUtilityFunction::~ModifiedVivaceUtilityFunction() = default;
+
+}  // namespace pcc
+}  // namespace webrtc

modules/congestion_controller/pcc/utility_function.h

@@ -0,0 +1,79 @@
+/*
+ *  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_PCC_UTILITY_FUNCTION_H_
+#define MODULES_CONGESTION_CONTROLLER_PCC_UTILITY_FUNCTION_H_
+
+#include "api/transport/network_control.h"
+#include "modules/congestion_controller/pcc/monitor_interval.h"
+
+namespace webrtc {
+namespace pcc {
+
+// Utility function is used by PCC to transform the performance statistics
+// (sending rate, loss rate, packets latency) gathered at one monitor interval
+// into a numerical value.
+// https://www.usenix.org/conference/nsdi18/presentation/dong
+class PccUtilityFunctionInterface {
+ public:
+  virtual double Compute(const PccMonitorInterval& monitor_interval) const = 0;
+  virtual ~PccUtilityFunctionInterface() = default;
+};
+
+// Vivace utility function were suggested in the paper "PCC Vivace:
+// Online-Learning Congestion Control", Mo Dong et all.
+class VivaceUtilityFunction : public PccUtilityFunctionInterface {
+ public:
+  VivaceUtilityFunction(double delay_gradient_coefficient,
+                        double loss_coefficient,
+                        double throughput_coefficient,
+                        double throughput_power,
+                        double delay_gradient_threshold,
+                        double delay_gradient_negative_bound);
+  double Compute(const PccMonitorInterval& monitor_interval) const override;
+  ~VivaceUtilityFunction() override;
+
+ private:
+  const double delay_gradient_coefficient_;
+  const double loss_coefficient_;
+  const double throughput_power_;
+  const double throughput_coefficient_;
+  const double delay_gradient_threshold_;
+  const double delay_gradient_negative_bound_;
+};
+
+// This utility function were obtained by tuning Vivace utility function.
+// The main difference is that gradient of modified utilify funtion (as well as
+// rate updates) scales proportionally to the sending rate which leads to
+// better performance in case of single sender.
+class ModifiedVivaceUtilityFunction : public PccUtilityFunctionInterface {
+ public:
+  ModifiedVivaceUtilityFunction(double delay_gradient_coefficient,
+                                double loss_coefficient,
+                                double throughput_coefficient,
+                                double throughput_power,
+                                double delay_gradient_threshold,
+                                double delay_gradient_negative_bound);
+  double Compute(const PccMonitorInterval& monitor_interval) const override;
+  ~ModifiedVivaceUtilityFunction() override;
+
+ private:
+  const double delay_gradient_coefficient_;
+  const double loss_coefficient_;
+  const double throughput_power_;
+  const double throughput_coefficient_;
+  const double delay_gradient_threshold_;
+  const double delay_gradient_negative_bound_;
+};
+
+}  // namespace pcc
+}  // namespace webrtc
+
+#endif  // MODULES_CONGESTION_CONTROLLER_PCC_UTILITY_FUNCTION_H_

modules/congestion_controller/pcc/utility_function_unittest.cc

@@ -0,0 +1,102 @@
+/*
+ *  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 <vector>
+
+#include "modules/congestion_controller/pcc/utility_function.h"
+#include "test/gtest.h"
+
+namespace webrtc {
+namespace pcc {
+namespace test {
+namespace {
+constexpr double kLossCoefficient = 11.35;
+constexpr double kThroughputPower = 0.9;
+constexpr double kThroughputCoefficient = 1;
+constexpr double kDelayGradientNegativeBound = 10;
+
+const Timestamp kStartTime = Timestamp::us(0);
+const TimeDelta kPacketsDelta = TimeDelta::ms(1);
+const TimeDelta kIntervalDuration = TimeDelta::ms(100);
+const DataRate kSendingBitrate = DataRate::bps(1000);
+
+const DataSize kDefaultDataSize = DataSize::bytes(100);
+const TimeDelta kDefaultDelay = TimeDelta::ms(100);
+
+std::vector<PacketResult> CreatePacketResults(
+    const std::vector<Timestamp>& packets_send_times,
+    const std::vector<Timestamp>& packets_received_times = {},
+    const std::vector<DataSize>& packets_sizes = {}) {
+  std::vector<PacketResult> packet_results;
+  PacketResult packet_result;
+  SentPacket sent_packet;
+  for (size_t i = 0; i < packets_send_times.size(); ++i) {
+    sent_packet.send_time = packets_send_times[i];
+    if (packets_sizes.empty()) {
+      sent_packet.size = kDefaultDataSize;
+    } else {
+      sent_packet.size = packets_sizes[i];
+    }
+    packet_result.sent_packet = sent_packet;
+    if (packets_received_times.empty()) {
+      packet_result.receive_time = packets_send_times[i] + kDefaultDelay;
+    } else {
+      packet_result.receive_time = packets_received_times[i];
+    }
+    packet_results.push_back(packet_result);
+  }
+  return packet_results;
+}
+
+}  // namespace
+
+TEST(PccVivaceUtilityFunctionTest,
+     UtilityIsThroughputTermIfAllRestCoefficientsAreZero) {
+  VivaceUtilityFunction utility_function(0, 0, kThroughputCoefficient,
+                                         kThroughputPower, 0,
+                                         kDelayGradientNegativeBound);
+  PccMonitorInterval monitor_interval(kSendingBitrate, kStartTime,
+                                      kIntervalDuration);
+  monitor_interval.OnPacketsFeedback(CreatePacketResults(
+      {kStartTime + kPacketsDelta, kStartTime + 2 * kPacketsDelta,
+       kStartTime + 3 * kPacketsDelta, kStartTime + 2 * kIntervalDuration},
+      {kStartTime + kPacketsDelta + kDefaultDelay, Timestamp::Infinity(),
+       kStartTime + kDefaultDelay + 3 * kPacketsDelta, Timestamp::Infinity()},
+      {kDefaultDataSize, kDefaultDataSize, kDefaultDataSize,
+       kDefaultDataSize}));
+  EXPECT_DOUBLE_EQ(utility_function.Compute(monitor_interval),
+                   kThroughputCoefficient *
+                       std::pow(kSendingBitrate.bps(), kThroughputPower));
+}
+
+TEST(PccVivaceUtilityFunctionTest,
+     LossTermIsNonZeroIfLossCoefficientIsNonZero) {
+  VivaceUtilityFunction utility_function(
+      0, kLossCoefficient, kThroughputCoefficient, kThroughputPower, 0,
+      kDelayGradientNegativeBound);
+  PccMonitorInterval monitor_interval(kSendingBitrate, kStartTime,
+                                      kIntervalDuration);
+  monitor_interval.OnPacketsFeedback(CreatePacketResults(
+      {kStartTime + kPacketsDelta, kStartTime + 2 * kPacketsDelta,
+       kStartTime + 5 * kPacketsDelta, kStartTime + 2 * kIntervalDuration},
+      {kStartTime + kDefaultDelay, Timestamp::Infinity(),
+       kStartTime + kDefaultDelay, kStartTime + 3 * kIntervalDuration},
+      {}));
+  // The second packet was lost.
+  EXPECT_DOUBLE_EQ(utility_function.Compute(monitor_interval),
+                   kThroughputCoefficient *
+                           std::pow(kSendingBitrate.bps(), kThroughputPower) -
+                       kLossCoefficient * kSendingBitrate.bps() *
+                           monitor_interval.GetLossRate());
+}
+
+}  // namespace test
+}  // namespace pcc
+}  // namespace webrtc