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rtt_stats.go
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/
rtt_stats.go
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package congestion
import (
"time"
"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/utils"
)
const (
rttAlpha float32 = 0.125
oneMinusAlpha float32 = (1 - rttAlpha)
rttBeta float32 = 0.25
oneMinusBeta float32 = (1 - rttBeta)
// The default RTT used before an RTT sample is taken.
defaultInitialRTT = 100 * time.Millisecond
)
// RTTStats provides round-trip statistics
type RTTStats struct {
minRTT time.Duration
latestRTT time.Duration
smoothedRTT time.Duration
meanDeviation time.Duration
}
// NewRTTStats makes a properly initialized RTTStats object
func NewRTTStats() *RTTStats {
return &RTTStats{}
}
// MinRTT Returns the minRTT for the entire connection.
// May return Zero if no valid updates have occurred.
func (r *RTTStats) MinRTT() time.Duration { return r.minRTT }
// LatestRTT returns the most recent rtt measurement.
// May return Zero if no valid updates have occurred.
func (r *RTTStats) LatestRTT() time.Duration { return r.latestRTT }
// SmoothedRTT returns the EWMA smoothed RTT for the connection.
// May return Zero if no valid updates have occurred.
func (r *RTTStats) SmoothedRTT() time.Duration { return r.smoothedRTT }
// SmoothedOrInitialRTT returns the EWMA smoothed RTT for the connection.
// If no valid updates have occurred, it returns the initial RTT.
func (r *RTTStats) SmoothedOrInitialRTT() time.Duration {
if r.smoothedRTT != 0 {
return r.smoothedRTT
}
return defaultInitialRTT
}
// MeanDeviation gets the mean deviation
func (r *RTTStats) MeanDeviation() time.Duration { return r.meanDeviation }
// UpdateRTT updates the RTT based on a new sample.
func (r *RTTStats) UpdateRTT(sendDelta, ackDelay time.Duration, now time.Time) {
if sendDelta == utils.InfDuration || sendDelta <= 0 {
return
}
// Update r.minRTT first. r.minRTT does not use an rttSample corrected for
// ackDelay but the raw observed sendDelta, since poor clock granularity at
// the client may cause a high ackDelay to result in underestimation of the
// r.minRTT.
if r.minRTT == 0 || r.minRTT > sendDelta {
r.minRTT = sendDelta
}
// Correct for ackDelay if information received from the peer results in a
// an RTT sample at least as large as minRTT. Otherwise, only use the
// sendDelta.
sample := sendDelta
if sample-r.minRTT >= ackDelay {
sample -= ackDelay
}
r.latestRTT = sample
// First time call.
if r.smoothedRTT == 0 {
r.smoothedRTT = sample
r.meanDeviation = sample / 2
} else {
r.meanDeviation = time.Duration(oneMinusBeta*float32(r.meanDeviation/time.Microsecond)+rttBeta*float32(utils.AbsDuration(r.smoothedRTT-sample)/time.Microsecond)) * time.Microsecond
r.smoothedRTT = time.Duration((float32(r.smoothedRTT/time.Microsecond)*oneMinusAlpha)+(float32(sample/time.Microsecond)*rttAlpha)) * time.Microsecond
}
}
// OnConnectionMigration is called when connection migrates and rtt measurement needs to be reset.
func (r *RTTStats) OnConnectionMigration() {
r.latestRTT = 0
r.minRTT = 0
r.smoothedRTT = 0
r.meanDeviation = 0
}
// ExpireSmoothedMetrics 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.
func (r *RTTStats) ExpireSmoothedMetrics() {
r.meanDeviation = utils.MaxDuration(r.meanDeviation, utils.AbsDuration(r.smoothedRTT-r.latestRTT))
r.smoothedRTT = utils.MaxDuration(r.smoothedRTT, r.latestRTT)
}