diff options
Diffstat (limited to 'chromium/net/quic/congestion_control/rtt_stats.cc')
-rw-r--r-- | chromium/net/quic/congestion_control/rtt_stats.cc | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/chromium/net/quic/congestion_control/rtt_stats.cc b/chromium/net/quic/congestion_control/rtt_stats.cc new file mode 100644 index 00000000000..745deb58cb3 --- /dev/null +++ b/chromium/net/quic/congestion_control/rtt_stats.cc @@ -0,0 +1,129 @@ +// 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 "net/quic/congestion_control/rtt_stats.h" + +namespace net { + +namespace { + +// Default initial rtt used before any samples are received. +const int kInitialRttMs = 100; +const float kAlpha = 0.125f; +const float kOneMinusAlpha = (1 - kAlpha); +const float kBeta = 0.25f; +const float kOneMinusBeta = (1 - kBeta); +const float kHalfWindow = 0.5f; +const float kQuarterWindow = 0.25f; + +} // namespace + +RttStats::RttStats() + : latest_rtt_(QuicTime::Delta::Zero()), + min_rtt_(QuicTime::Delta::Zero()), + smoothed_rtt_(QuicTime::Delta::Zero()), + mean_deviation_(QuicTime::Delta::Zero()), + initial_rtt_us_(kInitialRttMs * base::Time::kMicrosecondsPerMillisecond), + num_min_rtt_samples_remaining_(0), + recent_min_rtt_window_(QuicTime::Delta::Infinite()) {} + +bool RttStats::HasUpdates() const { + return !smoothed_rtt_.IsZero(); +} + +void RttStats::SampleNewRecentMinRtt(uint32 num_samples) { + num_min_rtt_samples_remaining_ = num_samples; + new_min_rtt_ = RttSample(); +} + +// Updates the RTT based on a new sample. +void RttStats::UpdateRtt(QuicTime::Delta send_delta, + QuicTime::Delta ack_delay, + QuicTime now) { + QuicTime::Delta rtt_sample(QuicTime::Delta::Zero()); + if (send_delta > ack_delay) { + rtt_sample = send_delta.Subtract(ack_delay); + } else if (!HasUpdates()) { + // Even though we received information from the peer suggesting + // an invalid (negative) RTT, we can use the send delta as an + // approximation until we get a better estimate. + rtt_sample = send_delta; + } + + if (rtt_sample.IsInfinite() || rtt_sample.IsZero()) { + DVLOG(1) << "Ignoring rtt, because it's " + << (rtt_sample.IsZero() ? "Zero" : "Infinite"); + return; + } + // RTT can't be negative. + DCHECK_LT(0, rtt_sample.ToMicroseconds()); + + latest_rtt_ = rtt_sample; + // First time call or link delay decreases. + if (min_rtt_.IsZero() || min_rtt_ > rtt_sample) { + min_rtt_ = rtt_sample; + } + UpdateRecentMinRtt(rtt_sample, now); + // First time call. + if (!HasUpdates()) { + smoothed_rtt_ = rtt_sample; + mean_deviation_ = QuicTime::Delta::FromMicroseconds( + rtt_sample.ToMicroseconds() / 2); + } else { + mean_deviation_ = QuicTime::Delta::FromMicroseconds( + kOneMinusBeta * mean_deviation_.ToMicroseconds() + + kBeta * std::abs(smoothed_rtt_.Subtract(rtt_sample).ToMicroseconds())); + smoothed_rtt_ = smoothed_rtt_.Multiply(kOneMinusAlpha).Add( + rtt_sample.Multiply(kAlpha)); + DVLOG(1) << "Cubic; smoothed_rtt(us):" << smoothed_rtt_.ToMicroseconds() + << " mean_deviation(us):" << mean_deviation_.ToMicroseconds(); + } +} + +void RttStats::UpdateRecentMinRtt(QuicTime::Delta rtt_sample, QuicTime now) { + // Recent min_rtt update. + if (num_min_rtt_samples_remaining_ > 0) { + --num_min_rtt_samples_remaining_; + if (new_min_rtt_.rtt.IsZero() || rtt_sample <= new_min_rtt_.rtt) { + new_min_rtt_ = RttSample(rtt_sample, now); + } + if (num_min_rtt_samples_remaining_ == 0) { + quarter_window_rtt_ = half_window_rtt_ = recent_min_rtt_ = new_min_rtt_; + } + } + + // Update the three recent rtt samples. + if (recent_min_rtt_.rtt.IsZero() || rtt_sample <= recent_min_rtt_.rtt) { + recent_min_rtt_ = RttSample(rtt_sample, now); + quarter_window_rtt_ = half_window_rtt_ = recent_min_rtt_; + } else if (rtt_sample <= half_window_rtt_.rtt) { + half_window_rtt_ = RttSample(rtt_sample, now); + quarter_window_rtt_ = half_window_rtt_; + } else if (rtt_sample <= quarter_window_rtt_.rtt) { + quarter_window_rtt_ = RttSample(rtt_sample, now); + } + + // Expire old min rtt samples. + if (recent_min_rtt_.time < now.Subtract(recent_min_rtt_window_)) { + recent_min_rtt_ = half_window_rtt_; + half_window_rtt_ = quarter_window_rtt_; + quarter_window_rtt_ = RttSample(rtt_sample, now); + } else if (half_window_rtt_.time < + now.Subtract(recent_min_rtt_window_.Multiply(kHalfWindow))) { + half_window_rtt_ = quarter_window_rtt_; + quarter_window_rtt_ = RttSample(rtt_sample, now); + } else if (quarter_window_rtt_.time < + now.Subtract(recent_min_rtt_window_.Multiply(kQuarterWindow))) { + quarter_window_rtt_ = RttSample(rtt_sample, now); + } +} + +QuicTime::Delta RttStats::SmoothedRtt() const { + if (!HasUpdates()) { + return QuicTime::Delta::FromMicroseconds(initial_rtt_us_); + } + return smoothed_rtt_; +} + +} // namespace net |