79 lines
2.5 KiB
Go
79 lines
2.5 KiB
Go
package congestion
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import (
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"math"
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"time"
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"github.com/metacubex/quic-go/congestion"
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)
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const initialMaxDatagramSize = congestion.ByteCount(1252)
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const MinPacingDelay = time.Millisecond
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const TimerGranularity = time.Millisecond
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const maxBurstSizePackets = 10
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// The pacer implements a token bucket pacing algorithm.
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type pacer struct {
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budgetAtLastSent congestion.ByteCount
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maxDatagramSize congestion.ByteCount
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lastSentTime time.Time
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getAdjustedBandwidth func() uint64 // in bytes/s
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}
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func newPacer(getBandwidth func() Bandwidth) *pacer {
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p := &pacer{
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maxDatagramSize: initialMaxDatagramSize,
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getAdjustedBandwidth: func() uint64 {
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// Bandwidth is in bits/s. We need the value in bytes/s.
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bw := uint64(getBandwidth() / BytesPerSecond)
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// Use a slightly higher value than the actual measured bandwidth.
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// RTT variations then won't result in under-utilization of the congestion window.
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// Ultimately, this will result in sending packets as acknowledgments are received rather than when timers fire,
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// provided the congestion window is fully utilized and acknowledgments arrive at regular intervals.
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return bw * 5 / 4
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},
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}
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p.budgetAtLastSent = p.maxBurstSize()
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return p
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}
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func (p *pacer) SentPacket(sendTime time.Time, size congestion.ByteCount) {
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budget := p.Budget(sendTime)
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if size > budget {
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p.budgetAtLastSent = 0
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} else {
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p.budgetAtLastSent = budget - size
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}
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p.lastSentTime = sendTime
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}
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func (p *pacer) Budget(now time.Time) congestion.ByteCount {
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if p.lastSentTime.IsZero() {
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return p.maxBurstSize()
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}
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budget := p.budgetAtLastSent + (congestion.ByteCount(p.getAdjustedBandwidth())*congestion.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
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return min(p.maxBurstSize(), budget)
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}
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func (p *pacer) maxBurstSize() congestion.ByteCount {
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return max(
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congestion.ByteCount(uint64((MinPacingDelay+TimerGranularity).Nanoseconds())*p.getAdjustedBandwidth())/1e9,
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maxBurstSizePackets*p.maxDatagramSize,
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)
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}
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// TimeUntilSend returns when the next packet should be sent.
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// It returns the zero value of time.Time if a packet can be sent immediately.
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func (p *pacer) TimeUntilSend() time.Time {
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if p.budgetAtLastSent >= p.maxDatagramSize {
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return time.Time{}
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}
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return p.lastSentTime.Add(max(
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MinPacingDelay,
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time.Duration(math.Ceil(float64(p.maxDatagramSize-p.budgetAtLastSent)*1e9/float64(p.getAdjustedBandwidth())))*time.Nanosecond,
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))
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}
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func (p *pacer) SetMaxDatagramSize(s congestion.ByteCount) {
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p.maxDatagramSize = s
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}
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