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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "quic/core/congestion_control/rtt_stats.h"
#include <cstdlib> // std::abs
#include "quic/platform/api/quic_flag_utils.h"
#include "quic/platform/api/quic_flags.h"
#include "quic/platform/api/quic_logging.h"
namespace quic {
namespace {
const float kAlpha = 0.125f;
const float kOneMinusAlpha = (1 - kAlpha);
const float kBeta = 0.25f;
const float kOneMinusBeta = (1 - kBeta);
} // namespace
RttStats::RttStats()
: latest_rtt_(QuicTime::Delta::Zero()),
min_rtt_(QuicTime::Delta::Zero()),
smoothed_rtt_(QuicTime::Delta::Zero()),
previous_srtt_(QuicTime::Delta::Zero()),
mean_deviation_(QuicTime::Delta::Zero()),
calculate_standard_deviation_(false),
initial_rtt_(QuicTime::Delta::FromMilliseconds(kInitialRttMs)),
last_update_time_(QuicTime::Zero()),
ignore_max_ack_delay_(false) {}
void RttStats::ExpireSmoothedMetrics() {
mean_deviation_ = std::max(
mean_deviation_, QuicTime::Delta::FromMicroseconds(std::abs(
(smoothed_rtt_ - latest_rtt_).ToMicroseconds())));
smoothed_rtt_ = std::max(smoothed_rtt_, latest_rtt_);
}
// Updates the RTT based on a new sample.
void RttStats::UpdateRtt(QuicTime::Delta send_delta,
QuicTime::Delta ack_delay,
QuicTime now) {
if (send_delta.IsInfinite() || send_delta <= QuicTime::Delta::Zero()) {
QUIC_LOG_FIRST_N(WARNING, 3)
<< "Ignoring measured send_delta, because it's is "
<< "either infinite, zero, or negative. send_delta = "
<< send_delta.ToMicroseconds();
return;
}
last_update_time_ = now;
// Update min_rtt_ first. min_rtt_ does not use an rtt_sample corrected for
// ack_delay but the raw observed send_delta, since poor clock granularity at
// the client may cause a high ack_delay to result in underestimation of the
// min_rtt_.
if (min_rtt_.IsZero() || min_rtt_ > send_delta) {
min_rtt_ = send_delta;
}
QuicTime::Delta rtt_sample(send_delta);
previous_srtt_ = smoothed_rtt_;
if (ignore_max_ack_delay_) {
ack_delay = QuicTime::Delta::Zero();
}
// Correct for ack_delay if information received from the peer results in a
// an RTT sample at least as large as min_rtt. Otherwise, only use the
// send_delta.
if (rtt_sample > ack_delay) {
if (rtt_sample - min_rtt_ >= ack_delay) {
rtt_sample = rtt_sample - ack_delay;
}
}
latest_rtt_ = rtt_sample;
if (calculate_standard_deviation_) {
standard_deviation_calculator_.OnNewRttSample(rtt_sample, smoothed_rtt_);
}
// First time call.
if (smoothed_rtt_.IsZero()) {
smoothed_rtt_ = rtt_sample;
mean_deviation_ =
QuicTime::Delta::FromMicroseconds(rtt_sample.ToMicroseconds() / 2);
} else {
mean_deviation_ = QuicTime::Delta::FromMicroseconds(static_cast<int64_t>(
kOneMinusBeta * mean_deviation_.ToMicroseconds() +
kBeta * std::abs((smoothed_rtt_ - rtt_sample).ToMicroseconds())));
smoothed_rtt_ = kOneMinusAlpha * smoothed_rtt_ + kAlpha * rtt_sample;
QUIC_DVLOG(1) << " smoothed_rtt(us):" << smoothed_rtt_.ToMicroseconds()
<< " mean_deviation(us):" << mean_deviation_.ToMicroseconds();
}
}
void RttStats::OnConnectionMigration() {
latest_rtt_ = QuicTime::Delta::Zero();
min_rtt_ = QuicTime::Delta::Zero();
smoothed_rtt_ = QuicTime::Delta::Zero();
mean_deviation_ = QuicTime::Delta::Zero();
initial_rtt_ = QuicTime::Delta::FromMilliseconds(kInitialRttMs);
}
QuicTime::Delta RttStats::GetStandardOrMeanDeviation() const {
QUICHE_DCHECK(calculate_standard_deviation_);
if (!standard_deviation_calculator_.has_valid_standard_deviation) {
return mean_deviation_;
}
return standard_deviation_calculator_.CalculateStandardDeviation();
}
void RttStats::StandardDeviationCaculator::OnNewRttSample(
QuicTime::Delta rtt_sample,
QuicTime::Delta smoothed_rtt) {
double new_value = rtt_sample.ToMicroseconds();
if (smoothed_rtt.IsZero()) {
return;
}
has_valid_standard_deviation = true;
const double delta = new_value - smoothed_rtt.ToMicroseconds();
m2 = kOneMinusBeta * m2 + kBeta * pow(delta, 2);
}
QuicTime::Delta
RttStats::StandardDeviationCaculator::CalculateStandardDeviation() const {
QUICHE_DCHECK(has_valid_standard_deviation);
return QuicTime::Delta::FromMicroseconds(sqrt(m2));
}
void RttStats::CloneFrom(const RttStats& stats) {
latest_rtt_ = stats.latest_rtt_;
min_rtt_ = stats.min_rtt_;
smoothed_rtt_ = stats.smoothed_rtt_;
previous_srtt_ = stats.previous_srtt_;
mean_deviation_ = stats.mean_deviation_;
standard_deviation_calculator_ = stats.standard_deviation_calculator_;
calculate_standard_deviation_ = stats.calculate_standard_deviation_;
initial_rtt_ = stats.initial_rtt_;
last_update_time_ = stats.last_update_time_;
ignore_max_ack_delay_ = stats.ignore_max_ack_delay_;
}
} // namespace quic
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