mirror of
https://github.com/refraction-networking/uquic.git
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84 lines
2.6 KiB
Go
84 lines
2.6 KiB
Go
package congestion
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import (
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"time"
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"github.com/refraction-networking/uquic/internal/protocol"
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)
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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 protocol.ByteCount
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maxDatagramSize protocol.ByteCount
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lastSentTime time.Time
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adjustedBandwidth 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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adjustedBandwidth: 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 protocol.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) protocol.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 + (protocol.ByteCount(p.adjustedBandwidth())*protocol.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
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if budget < 0 { // protect against overflows
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budget = protocol.MaxByteCount
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}
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return min(p.maxBurstSize(), budget)
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}
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func (p *pacer) maxBurstSize() protocol.ByteCount {
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return max(
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protocol.ByteCount(uint64((protocol.MinPacingDelay+protocol.TimerGranularity).Nanoseconds())*p.adjustedBandwidth())/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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diff := 1e9 * uint64(p.maxDatagramSize-p.budgetAtLastSent)
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bw := p.adjustedBandwidth()
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// We might need to round up this value.
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// Otherwise, we might have a budget (slightly) smaller than the datagram size when the timer expires.
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d := diff / bw
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// this is effectively a math.Ceil, but using only integer math
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if diff%bw > 0 {
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d++
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}
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return p.lastSentTime.Add(max(protocol.MinPacingDelay, time.Duration(d)*time.Nanosecond))
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}
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func (p *pacer) SetMaxDatagramSize(s protocol.ByteCount) {
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p.maxDatagramSize = s
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}
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