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use the actual maximum packet size in the pacer

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This commit is contained in:
Marten Seemann
2021-01-25 15:03:17 +08:00
parent dd8b21f264
commit 91a314258d
4 changed files with 60 additions and 31 deletions
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34
internal/congestion/pacer.go
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@@ -8,25 +8,29 @@ import (
"github.com/lucas-clemente/quic-go/internal/utils"
)
const maxBurstSize = 10 * maxDatagramSize
const maxBurstSizePackets = 10
// The pacer implements a token bucket pacing algorithm.
type pacer struct {
budgetAtLastSent protocol.ByteCount
maxDatagramSize 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 := &pacer{
maxDatagramSize: initialMaxDatagramSize,
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
}
@@ -52,18 +56,22 @@ func (p *pacer) Budget(now time.Time) protocol.ByteCount {
func (p *pacer) maxBurstSize() protocol.ByteCount {
return utils.MaxByteCount(
protocol.ByteCount(uint64((protocol.MinPacingDelay+protocol.TimerGranularity).Nanoseconds())*p.getAdjustedBandwidth())/1e9,
maxBurstSize,
maxBurstSizePackets*p.maxDatagramSize,
)
}
// 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 {
if p.budgetAtLastSent >= p.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,
time.Duration(math.Ceil(float64(p.maxDatagramSize-p.budgetAtLastSent)*1e9/float64(p.getAdjustedBandwidth())))*time.Nanosecond,
))
}
func (p *pacer) SetMaxDatagramSize(s protocol.ByteCount) {
p.maxDatagramSize = s
}