Add a new overuse estimator for the delay based BWE behind experiment.

webrtc/modules/congestion_controller/delay_based_bwe.cc

 /*
  *  Copyright (c) 2016 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 "webrtc/modules/congestion_controller/delay_based_bwe.h"
 
 #include <algorithm>
 #include <cmath>
+#include <string>
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/modules/congestion_controller/include/congestion_controller.h"
 #include "webrtc/modules/pacing/paced_sender.h"
 #include "webrtc/modules/remote_bitrate_estimator/include/remote_bitrate_estimator.h"
 #include "webrtc/system_wrappers/include/field_trial.h"
 #include "webrtc/system_wrappers/include/metrics.h"
 #include "webrtc/typedefs.h"
 
 namespace {
 constexpr int kTimestampGroupLengthMs = 5;
 constexpr int kAbsSendTimeFraction = 18;
 constexpr int kAbsSendTimeInterArrivalUpshift = 8;
 constexpr int kInterArrivalShift =
     kAbsSendTimeFraction + kAbsSendTimeInterArrivalUpshift;
 constexpr double kTimestampToMs =
     1000.0 / static_cast<double>(1 << kInterArrivalShift);
 // This ssrc is used to fulfill the current API but will be removed
 // after the API has been changed.
 constexpr uint32_t kFixedSsrc = 0;
 constexpr int kInitialRateWindowMs = 500;
 constexpr int kRateWindowMs = 150;
 
+constexpr size_t kDefaultTrendlineWindowSize = 20;
+constexpr double kDefaultTrendlineSmoothingCoeff = 0.9;
+constexpr double kDefaultTrendlineThresholdGain = 4.0;
+
 const char kBitrateEstimateExperiment[] = "WebRTC-ImprovedBitrateEstimate";
+const char kBweTrendlineFilterExperiment[] = "WebRTC-BweTrendlineFilter";
 
 bool BitrateEstimateExperimentIsEnabled() {
   return webrtc::field_trial::FindFullName(kBitrateEstimateExperiment) ==
          "Enabled";
 }
+
+bool TrendlineFilterExperimentIsEnabled() {
+  std::string experiment_string =
+      webrtc::field_trial::FindFullName(kBweTrendlineFilterExperiment);
+  // The experiment is enabled iff the field trial string begins with "Enabled".
+  return experiment_string.find("Enabled") == 0;
+}
+
+bool ReadTrendlineFilterExperimentParameters(size_t* window_points,
+                                             double* smoothing_coef,
+                                             double* threshold_gain) {
+  RTC_DCHECK(TrendlineFilterExperimentIsEnabled());
+  std::string experiment_string =
+      webrtc::field_trial::FindFullName(kBweTrendlineFilterExperiment);
+  int parsed_values = sscanf(experiment_string.c_str(), "Enabled-%zu,%lf,%lf",
+                             window_points, smoothing_coef, threshold_gain);
+  if (parsed_values == 3) {
+    if (2 <= *window_points && 0 <= *smoothing_coef && *smoothing_coef <= 1 &&

[stefan-webrtc, 2016/11/13 13:09:53]

I personally prefer having variables first and constants second, e.g.,
if (*window_points > 2 ...

[terelius, 2016/11/14 13:21:39]

In general I agree, but for the smoothing_coef I wanted to highlight that it is
in the interval [0,1], so I wanted to write something similar to the
mathematical relation 0 <= *smoothing_coef <= 1.

[stefan-webrtc, 2016/11/14 13:30:58]

Sounds good for smoothing_coef, but the other two doesn't really follow the same
logic?

[terelius, 2016/11/15 17:35:46]

The if statement is redundant if we CHECK anyway. Removed.

[stefan-webrtc, 2016/11/16 15:11:20]

Acknowledged.

+        0 <= *threshold_gain)
+      return true;
+    if (*window_points < 2)
+      LOG(LS_ERROR) << "Needs at least 2 points to fit a trend line.";

[stefan-webrtc, 2016/11/13 13:09:53]

Should we perhaps DCHECK on all broken configurations instead?

[terelius, 2016/11/14 13:21:39]

It would not give us any alert if we misconfigure the parameters in release
builds. Would CHECK be appropriate?

[stefan-webrtc, 2016/11/14 13:30:58]

Yes, then I think we should CHECK as it would be bad if we didn't catch those
issues.

[terelius, 2016/11/15 17:35:46]

Done.

+    if (*smoothing_coef < 0 || 1 < *smoothing_coef)
+      LOG(LS_ERROR)
+          << "Coefficient needs to be between 0 and 1 for weighted average.";
+    if (*threshold_gain < 0)
+      LOG(LS_ERROR) << "Threshold gain needs to be positive.";
+  }
+  LOG(LS_ERROR) << "Failed to parse parameters for BweTrendlineFilter "
+                   "experiment from field trial string.";
+  *window_points = kDefaultTrendlineWindowSize;
+  *smoothing_coef = kDefaultTrendlineSmoothingCoeff;
+  *threshold_gain = kDefaultTrendlineThresholdGain;
+  return false;
+}
+
 }  // namespace
 
 namespace webrtc {
+
 DelayBasedBwe::BitrateEstimator::BitrateEstimator()
     : sum_(0),
       current_win_ms_(0),
       prev_time_ms_(-1),
       bitrate_estimate_(-1.0f),
       bitrate_estimate_var_(50.0f),
       old_estimator_(kBitrateWindowMs, 8000),
       in_experiment_(BitrateEstimateExperimentIsEnabled()) {}
 
 void DelayBasedBwe::BitrateEstimator::Update(int64_t now_ms, int bytes) {
@@ skipping 65 matching lines @@
 
 rtc::Optional<uint32_t> DelayBasedBwe::BitrateEstimator::bitrate_bps() const {
   if (bitrate_estimate_ < 0.f)
     return rtc::Optional<uint32_t>();
   return rtc::Optional<uint32_t>(bitrate_estimate_ * 1000);
 }
 
 DelayBasedBwe::DelayBasedBwe(Clock* clock)
     : clock_(clock),
       inter_arrival_(),
-      estimator_(),
+      kalman_estimator_(),
+      trendline_estimator_(),
       detector_(OverUseDetectorOptions()),
       receiver_incoming_bitrate_(),
       last_update_ms_(-1),
       last_seen_packet_ms_(-1),
-      uma_recorded_(false) {
+      uma_recorded_(false),
+      trendline_window_size_(kDefaultTrendlineWindowSize),
+      trendline_smoothing_coeff_(kDefaultTrendlineSmoothingCoeff),
+      trendline_threshold_gain_(kDefaultTrendlineThresholdGain),
+      in_trendline_experiment_(TrendlineFilterExperimentIsEnabled()) {
+  if (in_trendline_experiment_) {
+    ReadTrendlineFilterExperimentParameters(&trendline_window_size_,
+                                            &trendline_smoothing_coeff_,
+                                            &trendline_threshold_gain_);
+  }
   network_thread_.DetachFromThread();
 }
 
 DelayBasedBwe::Result DelayBasedBwe::IncomingPacketFeedbackVector(
     const std::vector<PacketInfo>& packet_feedback_vector) {
   RTC_DCHECK(network_thread_.CalledOnValidThread());
   if (!uma_recorded_) {
     RTC_HISTOGRAM_ENUMERATION(kBweTypeHistogram,
                               BweNames::kSendSideTransportSeqNum,
                               BweNames::kBweNamesMax);
@@ skipping 13 matching lines @@
   int64_t now_ms = clock_->TimeInMilliseconds();
 
   receiver_incoming_bitrate_.Update(info.arrival_time_ms, info.payload_size);
   Result result;
   // Reset if the stream has timed out.
   if (last_seen_packet_ms_ == -1 ||
       now_ms - last_seen_packet_ms_ > kStreamTimeOutMs) {
     inter_arrival_.reset(
         new InterArrival((kTimestampGroupLengthMs << kInterArrivalShift) / 1000,
                          kTimestampToMs, true));
-    estimator_.reset(new OveruseEstimator(OverUseDetectorOptions()));
+    kalman_estimator_.reset(new OveruseEstimator(OverUseDetectorOptions()));
+    trendline_estimator_.reset(new TrendlineEstimator(
+        trendline_window_size_, trendline_smoothing_coeff_,
+        trendline_threshold_gain_));
   }
   last_seen_packet_ms_ = now_ms;
 
   uint32_t send_time_24bits =
       static_cast<uint32_t>(
           ((static_cast<uint64_t>(info.send_time_ms) << kAbsSendTimeFraction) +
            500) /
           1000) &
       0x00FFFFFF;
   // Shift up send time to use the full 32 bits that inter_arrival works with,
   // so wrapping works properly.
   uint32_t timestamp = send_time_24bits << kAbsSendTimeInterArrivalUpshift;
 
   uint32_t ts_delta = 0;
   int64_t t_delta = 0;
   int size_delta = 0;
   if (inter_arrival_->ComputeDeltas(timestamp, info.arrival_time_ms, now_ms,
                                     info.payload_size, &ts_delta, &t_delta,
                                     &size_delta)) {
     double ts_delta_ms = (1000.0 * ts_delta) / (1 << kInterArrivalShift);
-    estimator_->Update(t_delta, ts_delta_ms, size_delta, detector_.State(),
+    if (in_trendline_experiment_) {
+      trendline_estimator_->Update(t_delta, ts_delta_ms, info.arrival_time_ms);
+      detector_.Detect(trendline_estimator_->trendline_slope(), ts_delta_ms,
+                       trendline_estimator_->num_of_deltas(),
                        info.arrival_time_ms);
-    detector_.Detect(estimator_->offset(), ts_delta_ms,
-                     estimator_->num_of_deltas(), info.arrival_time_ms);
+
+    } else {
+      kalman_estimator_->Update(t_delta, ts_delta_ms, size_delta,
+                                detector_.State(), info.arrival_time_ms);
+      detector_.Detect(kalman_estimator_->offset(), ts_delta_ms,
+                       kalman_estimator_->num_of_deltas(),
+                       info.arrival_time_ms);
+    }
   }
 
   int probing_bps = 0;
   if (info.probe_cluster_id != PacketInfo::kNotAProbe) {
     probing_bps = probe_bitrate_estimator_.HandleProbeAndEstimateBitrate(info);
   }
   rtc::Optional<uint32_t> acked_bitrate_bps =
       receiver_incoming_bitrate_.bitrate_bps();
   // Currently overusing the bandwidth.
   if (detector_.State() == kBwOverusing) {
@@ skipping 21 matching lines @@
   if (result.updated)
     last_update_ms_ = now_ms;
 
   return result;
 }
 
 bool DelayBasedBwe::UpdateEstimate(int64_t arrival_time_ms,
                                    int64_t now_ms,
                                    rtc::Optional<uint32_t> acked_bitrate_bps,
                                    uint32_t* target_bitrate_bps) {
-  const RateControlInput input(detector_.State(), acked_bitrate_bps,
-                               estimator_->var_noise());
+  // TODO(terelius): RateControlInput::noise_var is deprecated and will be
+  // removed. In the meantime, we set it to zero.
+  const RateControlInput input(detector_.State(), acked_bitrate_bps, 0);
   rate_control_.Update(&input, now_ms);
   *target_bitrate_bps = rate_control_.UpdateBandwidthEstimate(now_ms);
   return rate_control_.ValidEstimate();
 }
 
 void DelayBasedBwe::OnRttUpdate(int64_t avg_rtt_ms, int64_t max_rtt_ms) {
   rate_control_.SetRtt(avg_rtt_ms);
 }
 
 bool DelayBasedBwe::LatestEstimate(std::vector<uint32_t>* ssrcs,
@@ skipping 11 matching lines @@
   *bitrate_bps = rate_control_.LatestEstimate();
   return true;
 }
 
 void DelayBasedBwe::SetMinBitrate(int min_bitrate_bps) {
   // Called from both the configuration thread and the network thread. Shouldn't
   // be called from the network thread in the future.
   rate_control_.SetMinBitrate(min_bitrate_bps);
 }
 }  // namespace webrtc