Probing: Add support for exponential startup probing

webrtc/modules/congestion_controller/probe_controller.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/probe_controller.h"
+
+#include <initializer_list>
+
+#include "webrtc/base/logging.h"
+
+namespace webrtc {
+
+namespace {
+
+// Number of deltas between probes per cluster. On the very first cluster,
+// we will need kProbeDeltasPerCluster + 1 probes, but on a cluster following
+// another, we need kProbeDeltasPerCluster probes.
+constexpr int kProbeDeltasPerCluster = 5;
+
+// Maximum waiting time from the time of initiating probing to getting
+// the measured results back.
+constexpr int64_t kMaxWaitingTimeForProbingResultMs = 1000;
+
+// Value of |min_bitrate_to_probe_further_bps_| that indicates
+// further probing is disabled.
+constexpr int kExponentialProbingDisabled = 0;
+
+}  // namespace
+
+ProbeController::ProbeController(PacedSender* pacer, Clock* clock)
+    : pacer_(pacer),
+      clock_(clock),
+      state_(State::kInit),
+      min_bitrate_to_probe_further_bps_(kExponentialProbingDisabled),
+      time_last_probing_initiated_ms_(0),
+      estimated_bitrate_bps_(0),
+      max_bitrate_bps_(0) {}
+
+void ProbeController::SetBitrates(int min_bitrate_bps,
+                                  int start_bitrate_bps,
+                                  int max_bitrate_bps) {
+  rtc::CritScope cs(&critsect_);
+  if (state_ == State::kInit) {
+    // When probing at 1.8 Mbps ( 6x 300), this represents a threshold of
+    // 1.2 Mbps to continue probing.
+    InitiateProbing({3 * start_bitrate_bps, 6 * start_bitrate_bps},
+                    4 * start_bitrate_bps);
+  }
+
+  // Only do probing if:
+  //   - we are mid-call, which we consider to be if
+  //     |estimated_bitrate_bps_| != 0, and
+  //   - the current bitrate is lower than the new |max_bitrate_bps|, and
+  //   - we actually want to increase the |max_bitrate_bps_|.
+  if (estimated_bitrate_bps_ != 0 && estimated_bitrate_bps_ < max_bitrate_bps &&
+      max_bitrate_bps > max_bitrate_bps_) {
+    InitiateProbing({max_bitrate_bps}, kExponentialProbingDisabled);
+  }
+  max_bitrate_bps_ = max_bitrate_bps;
+}
+
+void ProbeController::SetEstimatedBitrate(int bitrate_bps) {
+  rtc::CritScope cs(&critsect_);
+  if (state_ == State::kWaitingForProbingResult) {
+    if ((clock_->TimeInMilliseconds() - time_last_probing_initiated_ms_) >
+        kMaxWaitingTimeForProbingResultMs) {
+      LOG(LS_INFO) << "kWaitingForProbingResult: timeout";
+      state_ = State::kProbingComplete;
+      min_bitrate_to_probe_further_bps_ = kExponentialProbingDisabled;
+    } else {
+      // Continue probing if probing results indicate channel has greater
+      // capacity.
+      LOG(LS_INFO) << "Measured bitrate: " << bitrate_bps
+                   << " Minimum to probe further: "
+                   << min_bitrate_to_probe_further_bps_;
+      if (min_bitrate_to_probe_further_bps_ != kExponentialProbingDisabled &&
+          bitrate_bps > min_bitrate_to_probe_further_bps_) {
+        // Double the probing bitrate and expect a minimum of 25% gain to
+        // continue probing.
+        InitiateProbing({2 * bitrate_bps}, 1.25 * bitrate_bps);
+      }
+    }
+  }
+  estimated_bitrate_bps_ = bitrate_bps;
+}
+
+void ProbeController::InitiateProbing(
+    std::initializer_list<int> bitrates_to_probe,
+    int min_bitrate_to_probe_further_bps) {
+  bool first_cluster = true;
+  for (int bitrate : bitrates_to_probe) {
+    if (first_cluster) {
+      pacer_->CreateProbeCluster(bitrate, kProbeDeltasPerCluster + 1);
+      first_cluster = false;
+    } else {
+      pacer_->CreateProbeCluster(bitrate, kProbeDeltasPerCluster);
+    }
+  }
+  min_bitrate_to_probe_further_bps_ = min_bitrate_to_probe_further_bps;
+  time_last_probing_initiated_ms_ = clock_->TimeInMilliseconds();
+  if (min_bitrate_to_probe_further_bps == kExponentialProbingDisabled)
+    state_ = State::kProbingComplete;
+  else
+    state_ = State::kWaitingForProbingResult;
+}
+
+}  // namespace webrtc