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/*
* 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 "modules/congestion_controller/probe_controller.h"
#include <algorithm>
#include <initializer_list>
#include "rtc_base/logging.h"
#include "rtc_base/numerics/safe_conversions.h"
#include "system_wrappers/include/field_trial.h"
#include "system_wrappers/include/metrics.h"
namespace webrtc {
namespace {
// 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;
// Default probing bitrate limit. Applied only when the application didn't
// specify max bitrate.
constexpr int64_t kDefaultMaxProbingBitrateBps = 5000000;
// Interval between probes when ALR periodic probing is enabled.
constexpr int64_t kAlrPeriodicProbingIntervalMs = 5000;
// Minimum probe bitrate percentage to probe further for repeated probes,
// relative to the previous probe. For example, if 1Mbps probe results in
// 80kbps, then we'll probe again at 1.6Mbps. In that case second probe won't be
// sent if we get 600kbps from the first one.
constexpr int kRepeatedProbeMinPercentage = 70;
// If the bitrate drops to a factor |kBitrateDropThreshold| or lower
// and we recover within |kBitrateDropTimeoutMs|, then we'll send
// a probe at a fraction |kProbeFractionAfterDrop| of the original bitrate.
constexpr double kBitrateDropThreshold = 0.66;
constexpr int kBitrateDropTimeoutMs = 5000;
constexpr double kProbeFractionAfterDrop = 0.85;
// Timeout for probing after leaving ALR. If the bitrate drops significantly,
// (as determined by the delay based estimator) and we leave ALR, then we will
// send a probe if we recover within |kLeftAlrTimeoutMs| ms.
constexpr int kAlrEndedTimeoutMs = 3000;
// The expected uncertainty of probe result (as a fraction of the target probe
// This is a limit on how often probing can be done when there is a BW
// drop detected in ALR.
constexpr int64_t kMinTimeBetweenAlrProbesMs = 5000;
// bitrate). Used to avoid probing if the probe bitrate is close to our current
// estimate.
constexpr double kProbeUncertainty = 0.05;
// Use probing to recover faster after large bitrate estimate drops.
constexpr char kBweRapidRecoveryExperiment[] =
"WebRTC-BweRapidRecoveryExperiment";
} // namespace
ProbeController::ProbeController(PacedSender* pacer, const Clock* clock)
: pacer_(pacer), clock_(clock), enable_periodic_alr_probing_(false) {
Reset();
in_rapid_recovery_experiment_ = webrtc::field_trial::FindFullName(
kBweRapidRecoveryExperiment) == "Enabled";
}
void ProbeController::SetBitrates(int64_t min_bitrate_bps,
int64_t start_bitrate_bps,
int64_t max_bitrate_bps) {
rtc::CritScope cs(&critsect_);
if (start_bitrate_bps > 0) {
start_bitrate_bps_ = start_bitrate_bps;
estimated_bitrate_bps_ = start_bitrate_bps;
} else if (start_bitrate_bps_ == 0) {
start_bitrate_bps_ = min_bitrate_bps;
}
// The reason we use the variable |old_max_bitrate_pbs| is because we
// need to set |max_bitrate_bps_| before we call InitiateProbing.
int64_t old_max_bitrate_bps = max_bitrate_bps_;
max_bitrate_bps_ = max_bitrate_bps;
switch (state_) {
case State::kInit:
if (network_state_ == kNetworkUp)
InitiateExponentialProbing();
break;
case State::kWaitingForProbingResult:
break;
case State::kProbingComplete:
// If the new max bitrate is higher than the old max bitrate and the
// estimate is lower than the new max bitrate then initiate probing.
if (estimated_bitrate_bps_ != 0 &&
old_max_bitrate_bps < max_bitrate_bps_ &&
estimated_bitrate_bps_ < max_bitrate_bps_) {
// The assumption is that if we jump more than 20% in the bandwidth
// estimate or if the bandwidth estimate is within 90% of the new
// max bitrate then the probing attempt was successful.
mid_call_probing_succcess_threshold_ =
std::min(estimated_bitrate_bps_ * 1.2, max_bitrate_bps_ * 0.9);
mid_call_probing_waiting_for_result_ = true;
mid_call_probing_bitrate_bps_ = max_bitrate_bps_;
RTC_HISTOGRAM_COUNTS_10000("WebRTC.BWE.MidCallProbing.Initiated",
max_bitrate_bps_ / 1000);
InitiateProbing(clock_->TimeInMilliseconds(), {max_bitrate_bps}, false);
}
break;
}
}
void ProbeController::OnNetworkStateChanged(NetworkState network_state) {
rtc::CritScope cs(&critsect_);
network_state_ = network_state;
if (network_state_ == kNetworkUp && state_ == State::kInit)
InitiateExponentialProbing();
}
void ProbeController::InitiateExponentialProbing() {
RTC_DCHECK(network_state_ == kNetworkUp);
RTC_DCHECK(state_ == State::kInit);
RTC_DCHECK_GT(start_bitrate_bps_, 0);
// When probing at 1.8 Mbps ( 6x 300), this represents a threshold of
// 1.2 Mbps to continue probing.
InitiateProbing(clock_->TimeInMilliseconds(),
{3 * start_bitrate_bps_, 6 * start_bitrate_bps_}, true);
}
void ProbeController::SetEstimatedBitrate(int64_t bitrate_bps) {
rtc::CritScope cs(&critsect_);
int64_t now_ms = clock_->TimeInMilliseconds();
if (mid_call_probing_waiting_for_result_ &&
bitrate_bps >= mid_call_probing_succcess_threshold_) {
RTC_HISTOGRAM_COUNTS_10000("WebRTC.BWE.MidCallProbing.Success",
mid_call_probing_bitrate_bps_ / 1000);
RTC_HISTOGRAM_COUNTS_10000("WebRTC.BWE.MidCallProbing.ProbedKbps",
bitrate_bps / 1000);
mid_call_probing_waiting_for_result_ = false;
}
if (state_ == State::kWaitingForProbingResult) {
// Continue probing if probing results indicate channel has greater
// capacity.
RTC_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.
InitiateProbing(now_ms, {2 * bitrate_bps}, true);
}
}
if (bitrate_bps < kBitrateDropThreshold * estimated_bitrate_bps_) {
time_of_last_large_drop_ms_ = now_ms;
bitrate_before_last_large_drop_bps_ = estimated_bitrate_bps_;
}
estimated_bitrate_bps_ = bitrate_bps;
}
void ProbeController::EnablePeriodicAlrProbing(bool enable) {
rtc::CritScope cs(&critsect_);
enable_periodic_alr_probing_ = enable;
}
void ProbeController::SetAlrEndedTimeMs(int64_t alr_end_time_ms) {
rtc::CritScope cs(&critsect_);
alr_end_time_ms_.emplace(alr_end_time_ms);
}
void ProbeController::RequestProbe() {
int64_t now_ms = clock_->TimeInMilliseconds();
rtc::CritScope cs(&critsect_);
// Called once we have returned to normal state after a large drop in
// estimated bandwidth. The current response is to initiate a single probe
// session (if not already probing) at the previous bitrate.
//
// If the probe session fails, the assumption is that this drop was a
// real one from a competing flow or a network change.
bool in_alr = pacer_->GetApplicationLimitedRegionStartTime().has_value();
bool alr_ended_recently =
(alr_end_time_ms_.has_value() &&
now_ms - alr_end_time_ms_.value() < kAlrEndedTimeoutMs);
if (in_alr || alr_ended_recently || in_rapid_recovery_experiment_) {
if (state_ == State::kProbingComplete) {
uint32_t suggested_probe_bps =
kProbeFractionAfterDrop * bitrate_before_last_large_drop_bps_;
uint32_t min_expected_probe_result_bps =
(1 - kProbeUncertainty) * suggested_probe_bps;
int64_t time_since_drop_ms = now_ms - time_of_last_large_drop_ms_;
int64_t time_since_probe_ms = now_ms - last_bwe_drop_probing_time_ms_;
if (min_expected_probe_result_bps > estimated_bitrate_bps_ &&
time_since_drop_ms < kBitrateDropTimeoutMs &&
time_since_probe_ms > kMinTimeBetweenAlrProbesMs) {
RTC_LOG(LS_INFO) << "Detected big bandwidth drop, start probing.";
// Track how often we probe in response to bandwidth drop in ALR.
RTC_HISTOGRAM_COUNTS_10000(
"WebRTC.BWE.BweDropProbingIntervalInS",
(now_ms - last_bwe_drop_probing_time_ms_) / 1000);
InitiateProbing(now_ms, {suggested_probe_bps}, false);
last_bwe_drop_probing_time_ms_ = now_ms;
}
}
}
}
void ProbeController::Reset() {
rtc::CritScope cs(&critsect_);
network_state_ = kNetworkUp;
state_ = State::kInit;
min_bitrate_to_probe_further_bps_ = kExponentialProbingDisabled;
time_last_probing_initiated_ms_ = 0;
estimated_bitrate_bps_ = 0;
start_bitrate_bps_ = 0;
max_bitrate_bps_ = 0;
int64_t now_ms = clock_->TimeInMilliseconds();
last_bwe_drop_probing_time_ms_ = now_ms;
alr_end_time_ms_.reset();
mid_call_probing_waiting_for_result_ = false;
time_of_last_large_drop_ms_ = now_ms;
bitrate_before_last_large_drop_bps_ = 0;
}
void ProbeController::Process() {
rtc::CritScope cs(&critsect_);
int64_t now_ms = clock_->TimeInMilliseconds();
if (now_ms - time_last_probing_initiated_ms_ >
kMaxWaitingTimeForProbingResultMs) {
mid_call_probing_waiting_for_result_ = false;
if (state_ == State::kWaitingForProbingResult) {
RTC_LOG(LS_INFO) << "kWaitingForProbingResult: timeout";
state_ = State::kProbingComplete;
min_bitrate_to_probe_further_bps_ = kExponentialProbingDisabled;
}
}
if (state_ != State::kProbingComplete || !enable_periodic_alr_probing_)
return;
// Probe bandwidth periodically when in ALR state.
rtc::Optional<int64_t> alr_start_time =
pacer_->GetApplicationLimitedRegionStartTime();
if (alr_start_time && estimated_bitrate_bps_ > 0) {
int64_t next_probe_time_ms =
std::max(*alr_start_time, time_last_probing_initiated_ms_) +
kAlrPeriodicProbingIntervalMs;
if (now_ms >= next_probe_time_ms) {
InitiateProbing(now_ms, {estimated_bitrate_bps_ * 2}, true);
}
}
}
void ProbeController::InitiateProbing(
int64_t now_ms,
std::initializer_list<int64_t> bitrates_to_probe,
bool probe_further) {
for (int64_t bitrate : bitrates_to_probe) {
RTC_DCHECK_GT(bitrate, 0);
int64_t max_probe_bitrate_bps =
max_bitrate_bps_ > 0 ? max_bitrate_bps_ : kDefaultMaxProbingBitrateBps;
if (bitrate > max_probe_bitrate_bps) {
bitrate = max_probe_bitrate_bps;
probe_further = false;
}
pacer_->CreateProbeCluster(rtc::dchecked_cast<int>(bitrate));
}
time_last_probing_initiated_ms_ = now_ms;
if (probe_further) {
state_ = State::kWaitingForProbingResult;
min_bitrate_to_probe_further_bps_ =
(*(bitrates_to_probe.end() - 1)) * kRepeatedProbeMinPercentage / 100;
} else {
state_ = State::kProbingComplete;
min_bitrate_to_probe_further_bps_ = kExponentialProbingDisabled;
}
}
} // namespace webrtc