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use a callback to pass the bandwidth to the pacer

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This commit is contained in:
Marten Seemann 2020-06-16 14:01:11 +07:00
parent 467e553f2b
commit 312b8d37f0
2 changed files with 15 additions and 17 deletions
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22
internal/congestion/pacer.go
View file

@ -14,11 +14,14 @@ const maxBurstSize = 10 * maxDatagramSize
type pacer struct {
budgetAtLastSent protocol.ByteCount
lastSentTime time.Time
bandwidth uint64 // in bytes / s
getBandwidth func() uint64 // in bytes/s
}
func newPacer(bw uint64) *pacer {
p := &pacer{bandwidth: bw}
func newPacer(getBandwidth func() Bandwidth) *pacer {
p := &pacer{getBandwidth: func() uint64 {
// Bandwidth is in bits/s. We need the value in bytes/s.
return uint64(getBandwidth() / BytesPerSecond)
}}
p.budgetAtLastSent = p.maxBurstSize()
return p
}
@ -33,24 +36,17 @@ func (p *pacer) SentPacket(sendTime time.Time, size protocol.ByteCount) {
p.lastSentTime = sendTime
}
func (p *pacer) SetBandwidth(bw uint64) {
if bw == 0 {
panic("zero bandwidth")
}
p.bandwidth = bw
}
func (p *pacer) Budget(now time.Time) protocol.ByteCount {
if p.lastSentTime.IsZero() {
return p.maxBurstSize()
}
budget := p.budgetAtLastSent + (protocol.ByteCount(p.bandwidth)*protocol.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
budget := p.budgetAtLastSent + (protocol.ByteCount(p.getBandwidth())*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.bandwidth)/1e9,
protocol.ByteCount(uint64((protocol.MinPacingDelay+protocol.TimerGranularity).Nanoseconds())*p.getBandwidth())/1e9,
maxBurstSize,
)
}
@ -62,6 +58,6 @@ func (p *pacer) TimeUntilSend() time.Time {
}
return p.lastSentTime.Add(utils.MaxDuration(
protocol.MinPacingDelay,
time.Duration(math.Ceil(float64(maxDatagramSize-p.budgetAtLastSent)*1e9/float64(p.bandwidth)))*time.Nanosecond,
time.Duration(math.Ceil(float64(maxDatagramSize-p.budgetAtLastSent)*1e9/float64(p.getBandwidth())))*time.Nanosecond,
))
}

10
internal/congestion/pacer_test.go
View file

@ -13,9 +13,11 @@ var _ = Describe("Pacer", func() {
var p *pacer
const packetsPerSecond = 42
var bandwidth uint64 // in bytes/s
BeforeEach(func() {
p = newPacer(packetsPerSecond * uint64(maxDatagramSize)) // bandwidth: 42 full-size packets per second
bandwidth = uint64(packetsPerSecond * maxDatagramSize) // 42 full-size packets per second
p = newPacer(func() Bandwidth { return Bandwidth(bandwidth) * BytesPerSecond })
})
It("allows a burst at the beginning", func() {
@ -26,7 +28,7 @@ var _ = Describe("Pacer", func() {
It("allows a big burst for high pacing rates", func() {
t := time.Now()
p.SetBandwidth(10000 * packetsPerSecond * uint64(maxDatagramSize))
bandwidth = uint64(10000 * packetsPerSecond * maxDatagramSize)
Expect(p.TimeUntilSend()).To(BeZero())
Expect(p.Budget(t)).To(BeNumerically(">", maxBurstSize))
})
@ -94,14 +96,14 @@ var _ = Describe("Pacer", func() {
It("changes the bandwidth", func() {
t := time.Now()
sendBurst(t)
p.SetBandwidth(uint64(maxDatagramSize)) // reduce the bandwidth to 1 packet per second
bandwidth = uint64(maxDatagramSize) // reduce the bandwidth to 1 packet per second
Expect(p.TimeUntilSend()).To(Equal(t.Add(time.Second)))
})
It("doesn't pace faster than the minimum pacing duration", func() {
t := time.Now()
sendBurst(t)
p.SetBandwidth(1e6 * uint64(maxDatagramSize))
bandwidth = uint64(1e6 * maxDatagramSize)
Expect(p.TimeUntilSend()).To(Equal(t.Add(protocol.MinPacingDelay)))
Expect(p.Budget(t.Add(protocol.MinPacingDelay))).To(Equal(protocol.ByteCount(protocol.MinPacingDelay) * maxDatagramSize * 1e6 / 1e9))
})