Make the BWE threshold adaptive.

webrtc/modules/remote_bitrate_estimator/overuse_detector.cc

 /*
  *  Copyright (c) 2012 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/remote_bitrate_estimator/overuse_detector.h"
 
 #include <algorithm>
+#include <sstream>
 #include <math.h>
 #include <stdlib.h>
 
+#include "webrtc/base/common.h"
 #include "webrtc/modules/remote_bitrate_estimator/include/bwe_defines.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/bwe_test_logging.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_utility.h"
+#include "webrtc/system_wrappers/interface/field_trial.h"
 #include "webrtc/system_wrappers/interface/trace.h"
 
 namespace webrtc {
 
-enum { kOverUsingTimeThreshold = 100 };
+enum { kOverUsingTimeThreshold = 10 };
+const char* kAdaptiveThresholdExperiment = "WebRTC-AdaptiveBweThreshold";
+const char* kEnabledPrefix = "Enabled";
+const size_t kEnabledPrefixLength = 7;
+const size_t kMinExperimentLength =

[mflodman, 2015/07/03 08:29:55]

Can you comment this.

[stefan-webrtc, 2015/07/03 13:45:11]

I changed it to be sizeof(kEnabledPrefix) - 1 instead.

+    kEnabledPrefixLength + 3;
+
+const double kMaxAdaptOffsetMs = 15.0;
 
 OveruseDetector::OveruseDetector(const OverUseDetectorOptions& options)
     : options_(options),
-      threshold_(options_.initial_threshold),
+      threshold_(12.5),

[mflodman, 2015/07/03 08:29:56]

Why 12.5 instead of 25?

[Gaetano Carlucci, 2015/07/03 10:54:28]

This aims to speed up the convergence of the adaptive threshold. If you look the
dynamics of the adaptive threshold here
http://c3lab.poliba.it/images/4/43/Ietf89-gcc.pdf (slide 4&5) it takes some
seconds to converge at the beginning of the video call. A smaller value reduces
this time.

[stefan-webrtc, 2015/07/03 13:45:10]

I think this makes a very little difference in practice, and most of the time
when we were under congestion the threshold was 12.5 before. Therefore I think
it's safe to set it to 12.5 as default. The option would be to set it to 25, but
then we still don't have the old behavior, and I would really like to avoid
keeping the logic to switch between 12.5 and 25...

+      last_update_ms_(-1),
       prev_offset_(0.0),
       time_over_using_(-1),
       overuse_counter_(0),
-      hypothesis_(kBwNormal) {}
+      hypothesis_(kBwNormal),
+      k_up_(0.01),
+      k_down_(0.00018) {
+  double k_up = 0.0;
+  double k_down = 0.0;
+  if (GetExperimentThresholds(&k_up, &k_down)) {
+    k_up_ = k_up;
+    k_down_ = k_down;
+  }
+}
 
 OveruseDetector::~OveruseDetector() {}
 
 BandwidthUsage OveruseDetector::State() const {
   return hypothesis_;
 }
 
-
-void OveruseDetector::SetRateControlRegion(RateControlRegion region) {
-  switch (region) {
-    case kRcMaxUnknown: {
-      threshold_ = options_.initial_threshold;
-      break;
-    }
-    case kRcAboveMax:
-    case kRcNearMax: {
-      threshold_ = options_.initial_threshold / 2;
-      break;
-    }
-  }
-}
-
 BandwidthUsage OveruseDetector::Detect(double offset,
                                        double ts_delta,
                                        int num_of_deltas,
                                        int64_t now_ms) {
   if (num_of_deltas < 2) {
     return kBwNormal;
   }
   const double prev_offset = prev_offset_;
   prev_offset_ = offset;
   const double T = std::min(num_of_deltas, 60) * offset;
   BWE_TEST_LOGGING_PLOT(1, "offset", now_ms, T);
   BWE_TEST_LOGGING_PLOT(1, "threshold", now_ms, threshold_);
-
   if (T > threshold_) {
     if (time_over_using_ == -1) {
       // Initialize the timer. Assume that we've been
       // over-using half of the time since the previous
       // sample.
       time_over_using_ = ts_delta / 2;
     } else {
       // Increment timer
       time_over_using_ += ts_delta;
     }
     overuse_counter_++;
     if (time_over_using_ > kOverUsingTimeThreshold
         && overuse_counter_ > 1) {
       if (offset >= prev_offset) {
         time_over_using_ = 0;
         overuse_counter_ = 0;
         hypothesis_ = kBwOverusing;
       }
     }
   } else if (T < -threshold_) {
     time_over_using_ = -1;
     overuse_counter_ = 0;
     hypothesis_ = kBwUnderusing;
   } else {
     time_over_using_ = -1;
     overuse_counter_ = 0;
     hypothesis_ = kBwNormal;
   }
+
+  UpdateThreshold(T, now_ms);
+
   return hypothesis_;
 }
+
+void OveruseDetector::UpdateThreshold(double modified_offset, int64_t now_ms) {

[mflodman, 2015/07/03 08:29:56]

LG for the parts I know about this algorithm, but I don't have the full
knowledge to be 100% sure.

+  if (!AdaptiveThresholdExperimentIsEnabled())
+    return;
+
+  if (last_update_ms_ == -1)
+    last_update_ms_ = now_ms;
+
+  if (fabs(modified_offset) > threshold_ + kMaxAdaptOffsetMs) {
+    // Avoid adapting the threshold to big latency spikes, caused e.g.,
+    // by a sudden capacity drop.
+    last_update_ms_ = now_ms;
+    return;
+  }
+
+  const double k = fabs(modified_offset) < threshold_ ? k_down_ : k_up_;
+  threshold_ +=
+      k * (fabs(modified_offset) - threshold_) * (now_ms - last_update_ms_);
+
+  const double kMinThreshold = 6;
+  const double kMaxThreshold = 600;
+  threshold_ = std::min(std::max(threshold_, kMinThreshold), kMaxThreshold);
+
+  last_update_ms_ = now_ms;
+}
+
+bool OveruseDetector::AdaptiveThresholdExperimentIsEnabled() const {
+  std::string experiment_string =
+      webrtc::field_trial::FindFullName(kAdaptiveThresholdExperiment);
+  if (experiment_string.length() < kMinExperimentLength)
+    return false;
+  return experiment_string.substr(0, kEnabledPrefixLength) == kEnabledPrefix;
+}
+
+// Gets thresholds from the experiment name following the format
+// "WebRTC-AdaptiveBweThreshold/Enabled-0.5,0.002/".
+bool OveruseDetector::GetExperimentThresholds(double* k_up,
+                                              double* k_down) const {
+  if (!AdaptiveThresholdExperimentIsEnabled())
+    return false;
+  std::string experiment_string =
+      webrtc::field_trial::FindFullName(kAdaptiveThresholdExperiment);
+  std::stringstream ss(experiment_string.substr(
+      kEnabledPrefixLength + 1));
+  ss >> *k_up;
+  if (ss.peek() != ',')
+    return false;
+  ss.ignore();
+  ss >> *k_down;
+  if (ss.rdbuf()->in_avail() > 0)
+    return false;
+  return true;
+}
 }  // namespace webrtc