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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/goog_cc/probe_controller.h"
#include <algorithm>
#include <initializer_list>
#include <string>
#include "api/units/data_rate.h"
#include "api/units/time_delta.h"
#include "api/units/timestamp.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/numerics/safe_conversions.h"
#include "system_wrappers/include/metrics.h"
namespace webrtc {
namespace {
// The minimum number probing packets used.
constexpr int kMinProbePacketsSent = 5;
// The minimum probing duration in ms.
constexpr int kMinProbeDurationMs = 15;
// 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";
// Never probe higher than configured by OnMaxTotalAllocatedBitrate().
constexpr char kCappedProbingFieldTrialName[] = "WebRTC-BweCappedProbing";
} // namespace
ProbeController::ProbeController(const WebRtcKeyValueConfig* key_value_config)
: enable_periodic_alr_probing_(false),
in_rapid_recovery_experiment_(
key_value_config->Lookup(kBweRapidRecoveryExperiment)
.find("Enabled") == 0),
limit_probes_with_allocateable_rate_(
key_value_config->Lookup(kCappedProbingFieldTrialName)
.find("Disabled") != 0) {
Reset(0);
}
ProbeController::~ProbeController() {}
std::vector<ProbeClusterConfig> ProbeController::SetBitrates(
int64_t min_bitrate_bps,
int64_t start_bitrate_bps,
int64_t max_bitrate_bps,
int64_t at_time_ms) {
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_available_)
return InitiateExponentialProbing(at_time_ms);
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);
return InitiateProbing(at_time_ms, {max_bitrate_bps}, false);
}
break;
}
return std::vector<ProbeClusterConfig>();
}
std::vector<ProbeClusterConfig> ProbeController::OnMaxTotalAllocatedBitrate(
int64_t max_total_allocated_bitrate,
int64_t at_time_ms) {
if (state_ == State::kProbingComplete &&
max_total_allocated_bitrate != max_total_allocated_bitrate_ &&
estimated_bitrate_bps_ != 0 &&
(max_bitrate_bps_ <= 0 || estimated_bitrate_bps_ < max_bitrate_bps_) &&
estimated_bitrate_bps_ < max_total_allocated_bitrate) {
max_total_allocated_bitrate_ = max_total_allocated_bitrate;
return InitiateProbing(at_time_ms, {max_total_allocated_bitrate}, false);
}
max_total_allocated_bitrate_ = max_total_allocated_bitrate;
return std::vector<ProbeClusterConfig>();
}
std::vector<ProbeClusterConfig> ProbeController::OnNetworkAvailability(
NetworkAvailability msg) {
network_available_ = msg.network_available;
if (!network_available_ && state_ == State::kWaitingForProbingResult) {
state_ = State::kProbingComplete;
min_bitrate_to_probe_further_bps_ = kExponentialProbingDisabled;
}
if (network_available_ && state_ == State::kInit && start_bitrate_bps_ > 0)
return InitiateExponentialProbing(msg.at_time.ms());
return std::vector<ProbeClusterConfig>();
}
std::vector<ProbeClusterConfig> ProbeController::InitiateExponentialProbing(
int64_t at_time_ms) {
RTC_DCHECK(network_available_);
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.
return InitiateProbing(
at_time_ms, {3 * start_bitrate_bps_, 6 * start_bitrate_bps_}, true);
}
std::vector<ProbeClusterConfig> ProbeController::SetEstimatedBitrate(
int64_t bitrate_bps,
int64_t at_time_ms) {
int64_t now_ms = at_time_ms;
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;
}
std::vector<ProbeClusterConfig> pending_probes;
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.
pending_probes = 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;
return pending_probes;
}
void ProbeController::EnablePeriodicAlrProbing(bool enable) {
enable_periodic_alr_probing_ = enable;
}
void ProbeController::SetAlrStartTimeMs(
absl::optional<int64_t> alr_start_time_ms) {
alr_start_time_ms_ = alr_start_time_ms;
}
void ProbeController::SetAlrEndedTimeMs(int64_t alr_end_time_ms) {
alr_end_time_ms_.emplace(alr_end_time_ms);
}
std::vector<ProbeClusterConfig> ProbeController::RequestProbe(
int64_t at_time_ms) {
// 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 = alr_start_time_ms_.has_value();
bool alr_ended_recently =
(alr_end_time_ms_.has_value() &&
at_time_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 = at_time_ms - time_of_last_large_drop_ms_;
int64_t time_since_probe_ms = at_time_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",
(at_time_ms - last_bwe_drop_probing_time_ms_) / 1000);
return InitiateProbing(at_time_ms, {suggested_probe_bps}, false);
last_bwe_drop_probing_time_ms_ = at_time_ms;
}
}
}
return std::vector<ProbeClusterConfig>();
}
std::vector<ProbeClusterConfig> ProbeController::InitiateCapacityProbing(
int64_t bitrate_bps,
int64_t at_time_ms) {
if (state_ != State::kWaitingForProbingResult) {
RTC_DCHECK(network_available_);
return InitiateProbing(at_time_ms, {2 * bitrate_bps}, true);
}
return std::vector<ProbeClusterConfig>();
}
void ProbeController::SetMaxBitrate(int64_t max_bitrate_bps) {
max_bitrate_bps_ = max_bitrate_bps;
}
void ProbeController::Reset(int64_t at_time_ms) {
network_available_ = true;
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 = at_time_ms;
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;
max_total_allocated_bitrate_ = 0;
}
std::vector<ProbeClusterConfig> ProbeController::Process(int64_t at_time_ms) {
int64_t now_ms = at_time_ms;
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 (enable_periodic_alr_probing_ && state_ == State::kProbingComplete) {
// Probe bandwidth periodically when in ALR state.
if (alr_start_time_ms_ && estimated_bitrate_bps_ > 0) {
int64_t next_probe_time_ms =
std::max(*alr_start_time_ms_, time_last_probing_initiated_ms_) +
kAlrPeriodicProbingIntervalMs;
if (now_ms >= next_probe_time_ms) {
return InitiateProbing(now_ms, {estimated_bitrate_bps_ * 2}, true);
}
}
}
return std::vector<ProbeClusterConfig>();
}
std::vector<ProbeClusterConfig> ProbeController::InitiateProbing(
int64_t now_ms,
std::initializer_list<int64_t> bitrates_to_probe,
bool probe_further) {
std::vector<ProbeClusterConfig> pending_probes;
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 (limit_probes_with_allocateable_rate_ &&
max_total_allocated_bitrate_ > 0) {
// If a max allocated bitrate has been configured, allow probing up to 2x
// that rate. This allows some overhead to account for bursty streams,
// which otherwise would have to ramp up when the overshoot is already in
// progress.
// It also avoids minor quality reduction caused by probes often being
// received at slightly less than the target probe bitrate.
max_probe_bitrate_bps =
std::min(max_probe_bitrate_bps, max_total_allocated_bitrate_ * 2);
}
if (bitrate > max_probe_bitrate_bps) {
bitrate = max_probe_bitrate_bps;
probe_further = false;
}
ProbeClusterConfig config;
config.at_time = Timestamp::ms(now_ms);
config.target_data_rate = DataRate::bps(rtc::dchecked_cast<int>(bitrate));
config.target_duration = TimeDelta::ms(kMinProbeDurationMs);
config.target_probe_count = kMinProbePacketsSent;
pending_probes.push_back(config);
}
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;
}
return pending_probes;
}
} // namespace webrtc