Change TWCC send interval to reduce overhead on low BW situations.

webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.cc

 /*
  *  Copyright (c) 2015 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/remote_estimator_proxy.h"
 
 #include <limits>
+#include <algorithm>
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/system_wrappers/include/clock.h"
+#include "webrtc/modules/bitrate_controller/include/bitrate_controller.h"
 #include "webrtc/modules/pacing/packet_router.h"
 #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp.h"
 
 namespace webrtc {
 
 // TODO(sprang): Tune these!
-const int RemoteEstimatorProxy::kDefaultProcessIntervalMs = 50;
+const int RemoteEstimatorProxy::kMinPacketCountRecievedBitrate = 50;
 const int RemoteEstimatorProxy::kBackWindowMs = 500;
+const int RemoteEstimatorProxy::kMinSendIntervalMs = 50;
+const int RemoteEstimatorProxy::kMaxSendIntervalMs = 250;
 
 // The maximum allowed value for a timestamp in milliseconds. This is lower
 // than the numerical limit since we often convert to microseconds.
 static constexpr int64_t kMaxTimeMs =
     std::numeric_limits<int64_t>::max() / 1000;
 
-RemoteEstimatorProxy::RemoteEstimatorProxy(Clock* clock,
-                                           PacketRouter* packet_router)
+RemoteEstimatorProxy::RemoteEstimatorProxy(
+    Clock* clock,
+    PacketRouter* packet_router,
+    BitrateController* bitrate_controller)
     : clock_(clock),
       packet_router_(packet_router),
       last_process_time_ms_(-1),
       media_ssrc_(0),
       feedback_sequence_(0),
-      window_start_seq_(-1) {}
+      window_start_seq_(-1),
+      bitrate_controller_(bitrate_controller) {}
 
 RemoteEstimatorProxy::~RemoteEstimatorProxy() {}
 
 void RemoteEstimatorProxy::IncomingPacketFeedbackVector(
     const std::vector<PacketInfo>& packet_feedback_vector) {
   rtc::CritScope cs(&lock_);
   for (PacketInfo info : packet_feedback_vector)
     OnPacketArrival(info.sequence_number, info.arrival_time_ms);
 }
 
 void RemoteEstimatorProxy::IncomingPacket(int64_t arrival_time_ms,
                                           size_t payload_size,
                                           const RTPHeader& header) {
   if (!header.extension.hasTransportSequenceNumber) {
     LOG(LS_WARNING) << "RemoteEstimatorProxy: Incoming packet "
                        "is missing the transport sequence number extension!";
     return;
   }
   rtc::CritScope cs(&lock_);
   media_ssrc_ = header.ssrc;
 
   OnPacketArrival(header.extension.transportSequenceNumber, arrival_time_ms);
 }
 
 bool RemoteEstimatorProxy::LatestEstimate(std::vector<unsigned int>* ssrcs,
                                           unsigned int* bitrate_bps) const {
   return false;
 }
 
 int64_t RemoteEstimatorProxy::TimeUntilNextProcess() {

[minyue-webrtc, 2016/10/26 10:11:35]

general question: should we update send_interval_ms in this function?

It feels to me that this function is not necessarily called on a regular time
basis.

[michaelt, 2016/11/03 10:20:20]

Since send_interval_ms is just dependent on the actual BWE. I moved the
calculation of send_interval_ms to OnBitrateChanged.

[minyue-webrtc, 2016/11/03 10:39:38]

That reads much nicer to me.

   int64_t now = clock_->TimeInMilliseconds();
   int64_t time_until_next = 0;
-  if (last_process_time_ms_ != -1 &&
-      now - last_process_time_ms_ < kDefaultProcessIntervalMs) {
-    time_until_next = (last_process_time_ms_ + kDefaultProcessIntervalMs - now);
+  if (last_process_time_ms_ != -1) {
+    uint32_t bitrate = 0;
+    bitrate_controller_->AvailableBandwidth(&bitrate);
+    // Ipv4(20B) + UDP(8B) + SRTP(4B) + AverageTwccReport(20B)
+    constexpr int kTwccReportSize = 20 + 8 + 4 + 20;
+    int send_interval_ms =
+        kTwccReportSize * 8.0 * 1000.0 / (0.05 * bitrate) + 0.5;

[minyue-webrtc, 2016/10/26 10:11:35]

Would you add a comment, something like:

"Let TWCC occupy 5% of total bandwidth." 

[michaelt, 2016/11/03 10:20:20]

Done.

+    send_interval_ms = std::min(std::max(send_interval_ms, kMinSendIntervalMs),
+                                kMaxSendIntervalMs);
+    if (now - last_process_time_ms_ < send_interval_ms)
+      time_until_next = (last_process_time_ms_ + send_interval_ms - now);
   }
   return time_until_next;
 }
 
 void RemoteEstimatorProxy::Process() {
   last_process_time_ms_ = clock_->TimeInMilliseconds();
 
   bool more_to_build = true;
   while (more_to_build) {
     rtcp::TransportFeedback feedback_packet;
@@ skipping 88 matching lines @@
     // Note: Don't erase items from packet_arrival_times_ after sending, in case
     // they need to be re-sent after a reordering. Removal will be handled
     // by OnPacketArrival once packets are too old.
     window_start_seq_ = it->first + 1;
   }
 
   return true;
 }
 
 }  // namespace webrtc