Add probing to recover faster from large bitrate drops.

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.
  */
 
@@ skipping 39 matching lines @@
 
 bool BweSparseUpdateExperimentIsEnabled() {
   std::string experiment_string =
       webrtc::field_trial::FindFullName(kBweSparseUpdateExperiment);
   return experiment_string == "Enabled";
 }
 }  // namespace
 
 namespace webrtc {
 
+DelayBasedBwe::Result::Result()
+    : updated(false),
+      probe(false),
+      target_bitrate_bps(0),
+      recovered_from_overuse(false) {}
+
+DelayBasedBwe::Result::Result(bool probe, uint32_t target_bitrate_bps)
+    : updated(true),
+      probe(probe),
+      target_bitrate_bps(target_bitrate_bps),
+      recovered_from_overuse(false) {}
+
+DelayBasedBwe::Result::~Result() {}
+
 DelayBasedBwe::DelayBasedBwe(RtcEventLog* event_log, const Clock* clock)
     : event_log_(event_log),
       clock_(clock),
       inter_arrival_(),
       trendline_estimator_(),
       detector_(),
       last_seen_packet_ms_(-1),
       uma_recorded_(false),
       probe_bitrate_estimator_(event_log),
       trendline_window_size_(kDefaultTrendlineWindowSize),
@@ skipping 25 matching lines @@
   }
 
   if (!uma_recorded_) {
     RTC_HISTOGRAM_ENUMERATION(kBweTypeHistogram,
                               BweNames::kSendSideTransportSeqNum,
                               BweNames::kBweNamesMax);
     uma_recorded_ = true;
   }
   bool overusing = false;
   bool delayed_feedback = true;
+  bool recovered_from_overuse = false;
+  BandwidthUsage prev_detector_state = detector_.State();
   for (const auto& packet_feedback : packet_feedback_vector) {
     if (packet_feedback.send_time_ms < 0)
       continue;
     delayed_feedback = false;
     IncomingPacketFeedback(packet_feedback);
     if (!in_sparse_update_experiment_)
       overusing |= (detector_.State() == BandwidthUsage::kBwOverusing);
+    if (prev_detector_state == BandwidthUsage::kBwUnderusing &&
+        detector_.State() == BandwidthUsage::kBwNormal) {
+      recovered_from_overuse = true;
+    }
+    prev_detector_state = detector_.State();
   }
   if (in_sparse_update_experiment_)
     overusing = (detector_.State() == BandwidthUsage::kBwOverusing);
+
   if (delayed_feedback) {
     ++consecutive_delayed_feedbacks_;
     if (consecutive_delayed_feedbacks_ >= kMaxConsecutiveFailedLookups) {
       consecutive_delayed_feedbacks_ = 0;
       return OnLongFeedbackDelay(packet_feedback_vector.back().arrival_time_ms);
     }
   } else {
     consecutive_delayed_feedbacks_ = 0;
-    return MaybeUpdateEstimate(overusing, acked_bitrate_bps);
+    return MaybeUpdateEstimate(overusing, acked_bitrate_bps,
+                               recovered_from_overuse);
   }
   return Result();
 }
 
 DelayBasedBwe::Result DelayBasedBwe::OnLongFeedbackDelay(
     int64_t arrival_time_ms) {
   // Estimate should always be valid since a start bitrate always is set in the
   // Call constructor. An alternative would be to return an empty Result here,
   // or to estimate the throughput based on the feedback we received.
   RTC_DCHECK(rate_control_.ValidEstimate());
@@ skipping 48 matching lines @@
                      packet_feedback.arrival_time_ms);
   }
   if (packet_feedback.pacing_info.probe_cluster_id !=
       PacedPacketInfo::kNotAProbe) {
     probe_bitrate_estimator_.HandleProbeAndEstimateBitrate(packet_feedback);
   }
 }
 
 DelayBasedBwe::Result DelayBasedBwe::MaybeUpdateEstimate(
     bool overusing,
-    rtc::Optional<uint32_t> acked_bitrate_bps) {
+    rtc::Optional<uint32_t> acked_bitrate_bps,
+    bool recovered_from_overuse) {
   Result result;
   int64_t now_ms = clock_->TimeInMilliseconds();
 
   rtc::Optional<int> probe_bitrate_bps =
       probe_bitrate_estimator_.FetchAndResetLastEstimatedBitrateBps();
   // Currently overusing the bandwidth.
   if (overusing) {
     if (acked_bitrate_bps &&
         rate_control_.TimeToReduceFurther(now_ms, *acked_bitrate_bps)) {
       result.updated = UpdateEstimate(now_ms, acked_bitrate_bps, overusing,
@@ skipping 13 matching lines @@
     }
   } else {
     if (probe_bitrate_bps) {
       result.probe = true;
       result.updated = true;
       result.target_bitrate_bps = *probe_bitrate_bps;
       rate_control_.SetEstimate(*probe_bitrate_bps, now_ms);
     } else {
       result.updated = UpdateEstimate(now_ms, acked_bitrate_bps, overusing,
                                       &result.target_bitrate_bps);
+      result.recovered_from_overuse = recovered_from_overuse;
     }
   }
   if (result.updated) {
     BWE_TEST_LOGGING_PLOT(1, "target_bitrate_bps", now_ms,
                           result.target_bitrate_bps);
     if (event_log_ && (result.target_bitrate_bps != last_logged_bitrate_ ||
                        detector_.State() != last_logged_state_)) {
       event_log_->LogDelayBasedBweUpdate(result.target_bitrate_bps,
                                          detector_.State());
       last_logged_bitrate_ = result.target_bitrate_bps;
@@ skipping 46 matching lines @@
 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);
 }
 
 int64_t DelayBasedBwe::GetExpectedBwePeriodMs() const {
   return rate_control_.GetExpectedBandwidthPeriodMs();
 }
 }  // namespace webrtc