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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.
//
// A convenience class to store rtt samples and calculate smoothed rtt.
#ifndef NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
#define NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
#include <algorithm>
#include "base/basictypes.h"
#include "net/quic/quic_protocol.h"
#include "net/quic/quic_time.h"
namespace net {
namespace test {
class RttStatsPeer;
} // namespace test
class NET_EXPORT_PRIVATE RttStats {
public:
RttStats();
// Updates the RTT from an incoming ack which is received |send_delta| after
// the packet is sent and the peer reports the ack being delayed |ack_delay|.
void UpdateRtt(QuicTime::Delta send_delta,
QuicTime::Delta ack_delay,
QuicTime now);
// Causes the smoothed_rtt to be increased to the latest_rtt if the latest_rtt
// is larger. The mean deviation is increased to the most recent deviation if
// it's larger.
void ExpireSmoothedMetrics();
// Forces RttStats to sample a new recent min rtt within the next
// |num_samples| UpdateRtt calls.
void SampleNewRecentMinRtt(uint32 num_samples);
// Called when connection migrates and rtt measurement needs to be reset.
void OnConnectionMigration() {}
// Returns the EWMA smoothed RTT for the connection.
// May return Zero if no valid updates have occurred.
QuicTime::Delta smoothed_rtt() const {
return smoothed_rtt_;
}
int64 initial_rtt_us() const {
return initial_rtt_us_;
}
// Sets an initial RTT to be used for SmoothedRtt before any RTT updates.
void set_initial_rtt_us(int64 initial_rtt_us) {
if (initial_rtt_us <= 0) {
LOG(DFATAL) << "Attempt to set initial rtt to <= 0.";
return;
}
initial_rtt_us_ = initial_rtt_us;
}
// The most recent rtt measurement.
// May return Zero if no valid updates have occurred.
QuicTime::Delta latest_rtt() const {
return latest_rtt_;
}
// Returns the min_rtt for the entire connection.
// May return Zero if no valid updates have occurred.
QuicTime::Delta min_rtt() const {
return min_rtt_;
}
// Returns the min_rtt since SampleNewRecentMinRtt has been called, or the
// min_rtt for the entire connection if SampleNewMinRtt was never called.
QuicTime::Delta recent_min_rtt() const {
return recent_min_rtt_.rtt;
}
QuicTime::Delta mean_deviation() const {
return mean_deviation_;
}
// Sets how old a recent min rtt sample can be.
void set_recent_min_rtt_window(QuicTime::Delta recent_min_rtt_window) {
recent_min_rtt_window_ = recent_min_rtt_window;
}
private:
friend class test::RttStatsPeer;
// Used to track a sampled RTT window.
struct RttSample {
RttSample() : rtt(QuicTime::Delta::Zero()), time(QuicTime::Zero()) { }
RttSample(QuicTime::Delta rtt, QuicTime time) : rtt(rtt), time(time) { }
QuicTime::Delta rtt;
QuicTime time; // Time the rtt sample was recorded.
};
// Implements the resampling algorithm and the windowed min rtt algorithm.
void UpdateRecentMinRtt(QuicTime::Delta rtt_sample, QuicTime now);
QuicTime::Delta latest_rtt_;
QuicTime::Delta min_rtt_;
QuicTime::Delta smoothed_rtt_;
// Mean RTT deviation during this session.
// Approximation of standard deviation, the error is roughly 1.25 times
// larger than the standard deviation, for a normally distributed signal.
QuicTime::Delta mean_deviation_;
int64 initial_rtt_us_;
RttSample new_min_rtt_;
uint32 num_min_rtt_samples_remaining_;
// State variables for Kathleen Nichols MinRTT algorithm.
QuicTime::Delta recent_min_rtt_window_;
RttSample recent_min_rtt_; // a in the windowed algorithm.
RttSample half_window_rtt_; // b in the sampled algorithm.
RttSample quarter_window_rtt_; // c in the sampled algorithm.
DISALLOW_COPY_AND_ASSIGN(RttStats);
};
} // namespace net
#endif // NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
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