forked from quic-go/quic-go
33d058f4ee
The pacer returns the zero value of time.Time when a packet can be sent immediately. The session uses the zero value to unset the pacing deadline.
70 lines
2.2 KiB
Go
70 lines
2.2 KiB
Go
package congestion
|
|
|
|
import (
|
|
"math"
|
|
"time"
|
|
|
|
"github.com/lucas-clemente/quic-go/internal/protocol"
|
|
"github.com/lucas-clemente/quic-go/internal/utils"
|
|
)
|
|
|
|
const maxBurstSize = 10 * maxDatagramSize
|
|
|
|
// The pacer implements a token bucket pacing algorithm.
|
|
type pacer struct {
|
|
budgetAtLastSent protocol.ByteCount
|
|
lastSentTime time.Time
|
|
getAdjustedBandwidth func() uint64 // in bytes/s
|
|
}
|
|
|
|
func newPacer(getBandwidth func() Bandwidth) *pacer {
|
|
p := &pacer{getAdjustedBandwidth: func() uint64 {
|
|
// Bandwidth is in bits/s. We need the value in bytes/s.
|
|
bw := uint64(getBandwidth() / BytesPerSecond)
|
|
// Use a slightly higher value than the actual measured bandwidth.
|
|
// RTT variations then won't result in under-utilization of the congestion window.
|
|
// Ultimately, this will result in sending packets as acknowledgments are received rather than when timers fire,
|
|
// provided the congestion window is fully utilized and acknowledgments arrive at regular intervals.
|
|
return bw * 5 / 4
|
|
}}
|
|
p.budgetAtLastSent = p.maxBurstSize()
|
|
return p
|
|
}
|
|
|
|
func (p *pacer) SentPacket(sendTime time.Time, size protocol.ByteCount) {
|
|
budget := p.Budget(sendTime)
|
|
if size > budget {
|
|
p.budgetAtLastSent = 0
|
|
} else {
|
|
p.budgetAtLastSent = budget - size
|
|
}
|
|
p.lastSentTime = sendTime
|
|
}
|
|
|
|
func (p *pacer) Budget(now time.Time) protocol.ByteCount {
|
|
if p.lastSentTime.IsZero() {
|
|
return p.maxBurstSize()
|
|
}
|
|
budget := p.budgetAtLastSent + (protocol.ByteCount(p.getAdjustedBandwidth())*protocol.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
|
|
return utils.MinByteCount(p.maxBurstSize(), budget)
|
|
}
|
|
|
|
func (p *pacer) maxBurstSize() protocol.ByteCount {
|
|
return utils.MaxByteCount(
|
|
protocol.ByteCount(uint64((protocol.MinPacingDelay+protocol.TimerGranularity).Nanoseconds())*p.getAdjustedBandwidth())/1e9,
|
|
maxBurstSize,
|
|
)
|
|
}
|
|
|
|
// TimeUntilSend returns when the next packet should be sent.
|
|
// It returns the zero value of time.Time if a packet can be sent immediately.
|
|
func (p *pacer) TimeUntilSend() time.Time {
|
|
if p.budgetAtLastSent >= maxDatagramSize {
|
|
return time.Time{}
|
|
}
|
|
return p.lastSentTime.Add(utils.MaxDuration(
|
|
protocol.MinPacingDelay,
|
|
time.Duration(math.Ceil(float64(maxDatagramSize-p.budgetAtLastSent)*1e9/float64(p.getAdjustedBandwidth())))*time.Nanosecond,
|
|
))
|
|
}
|