319 lines
9.6 KiB
Go
319 lines
9.6 KiB
Go
package congestion
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import (
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"fmt"
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"time"
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"github.com/sagernet/quic-go/congestion"
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"github.com/sagernet/quic-go/logging"
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)
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const (
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maxBurstPackets = 3
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renoBeta = 0.7 // Reno backoff factor.
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minCongestionWindowPackets = 2
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initialCongestionWindow = 32
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)
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const (
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InvalidPacketNumber congestion.PacketNumber = -1
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MaxCongestionWindowPackets = 20000
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MaxByteCount = congestion.ByteCount(1<<62 - 1)
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)
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type cubicSender struct {
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hybridSlowStart HybridSlowStart
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rttStats congestion.RTTStatsProvider
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cubic *Cubic
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pacer *pacer
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clock Clock
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reno bool
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// Track the largest packet that has been sent.
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largestSentPacketNumber congestion.PacketNumber
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// Track the largest packet that has been acked.
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largestAckedPacketNumber congestion.PacketNumber
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// Track the largest packet number outstanding when a CWND cutback occurs.
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largestSentAtLastCutback congestion.PacketNumber
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// Whether the last loss event caused us to exit slowstart.
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// Used for stats collection of slowstartPacketsLost
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lastCutbackExitedSlowstart bool
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// Congestion window in bytes.
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congestionWindow congestion.ByteCount
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// Slow start congestion window in bytes, aka ssthresh.
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slowStartThreshold congestion.ByteCount
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// ACK counter for the Reno implementation.
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numAckedPackets uint64
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initialCongestionWindow congestion.ByteCount
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initialMaxCongestionWindow congestion.ByteCount
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maxDatagramSize congestion.ByteCount
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lastState logging.CongestionState
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tracer logging.ConnectionTracer
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}
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var _ congestion.CongestionControl = &cubicSender{}
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// NewCubicSender makes a new cubic sender
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func NewCubicSender(
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clock Clock,
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initialMaxDatagramSize congestion.ByteCount,
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reno bool,
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tracer logging.ConnectionTracer,
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) *cubicSender {
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return newCubicSender(
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clock,
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reno,
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initialMaxDatagramSize,
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initialCongestionWindow*initialMaxDatagramSize,
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MaxCongestionWindowPackets*initialMaxDatagramSize,
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tracer,
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)
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}
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func newCubicSender(
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clock Clock,
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reno bool,
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initialMaxDatagramSize,
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initialCongestionWindow,
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initialMaxCongestionWindow congestion.ByteCount,
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tracer logging.ConnectionTracer,
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) *cubicSender {
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c := &cubicSender{
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largestSentPacketNumber: InvalidPacketNumber,
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largestAckedPacketNumber: InvalidPacketNumber,
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largestSentAtLastCutback: InvalidPacketNumber,
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initialCongestionWindow: initialCongestionWindow,
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initialMaxCongestionWindow: initialMaxCongestionWindow,
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congestionWindow: initialCongestionWindow,
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slowStartThreshold: MaxByteCount,
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cubic: NewCubic(clock),
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clock: clock,
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reno: reno,
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tracer: tracer,
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maxDatagramSize: initialMaxDatagramSize,
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}
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c.pacer = newPacer(c.BandwidthEstimate)
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if c.tracer != nil {
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c.lastState = logging.CongestionStateSlowStart
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c.tracer.UpdatedCongestionState(logging.CongestionStateSlowStart)
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}
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return c
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}
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func (c *cubicSender) SetRTTStatsProvider(provider congestion.RTTStatsProvider) {
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c.rttStats = provider
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}
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// TimeUntilSend returns when the next packet should be sent.
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func (c *cubicSender) TimeUntilSend(_ congestion.ByteCount) time.Time {
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return c.pacer.TimeUntilSend()
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}
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func (c *cubicSender) HasPacingBudget(now time.Time) bool {
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return c.pacer.Budget(now) >= c.maxDatagramSize
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}
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func (c *cubicSender) maxCongestionWindow() congestion.ByteCount {
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return c.maxDatagramSize * MaxCongestionWindowPackets
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}
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func (c *cubicSender) minCongestionWindow() congestion.ByteCount {
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return c.maxDatagramSize * minCongestionWindowPackets
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}
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func (c *cubicSender) OnPacketSent(
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sentTime time.Time,
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_ congestion.ByteCount,
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packetNumber congestion.PacketNumber,
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bytes congestion.ByteCount,
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isRetransmittable bool,
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) {
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c.pacer.SentPacket(sentTime, bytes)
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if !isRetransmittable {
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return
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}
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c.largestSentPacketNumber = packetNumber
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c.hybridSlowStart.OnPacketSent(packetNumber)
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}
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func (c *cubicSender) CanSend(bytesInFlight congestion.ByteCount) bool {
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return bytesInFlight < c.GetCongestionWindow()
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}
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func (c *cubicSender) InRecovery() bool {
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return c.largestAckedPacketNumber != InvalidPacketNumber && c.largestAckedPacketNumber <= c.largestSentAtLastCutback
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}
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func (c *cubicSender) InSlowStart() bool {
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return c.GetCongestionWindow() < c.slowStartThreshold
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}
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func (c *cubicSender) GetCongestionWindow() congestion.ByteCount {
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return c.congestionWindow
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}
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func (c *cubicSender) MaybeExitSlowStart() {
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if c.InSlowStart() &&
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c.hybridSlowStart.ShouldExitSlowStart(c.rttStats.LatestRTT(), c.rttStats.MinRTT(), c.GetCongestionWindow()/c.maxDatagramSize) {
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// exit slow start
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c.slowStartThreshold = c.congestionWindow
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c.maybeTraceStateChange(logging.CongestionStateCongestionAvoidance)
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}
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}
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func (c *cubicSender) OnPacketAcked(
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ackedPacketNumber congestion.PacketNumber,
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ackedBytes congestion.ByteCount,
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priorInFlight congestion.ByteCount,
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eventTime time.Time,
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) {
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c.largestAckedPacketNumber = Max(ackedPacketNumber, c.largestAckedPacketNumber)
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if c.InRecovery() {
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return
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}
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c.maybeIncreaseCwnd(ackedPacketNumber, ackedBytes, priorInFlight, eventTime)
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if c.InSlowStart() {
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c.hybridSlowStart.OnPacketAcked(ackedPacketNumber)
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}
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}
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func (c *cubicSender) OnPacketLost(packetNumber congestion.PacketNumber, lostBytes, priorInFlight congestion.ByteCount) {
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// TCP NewReno (RFC6582) says that once a loss occurs, any losses in packets
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// already sent should be treated as a single loss event, since it's expected.
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if packetNumber <= c.largestSentAtLastCutback {
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return
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}
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c.lastCutbackExitedSlowstart = c.InSlowStart()
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c.maybeTraceStateChange(logging.CongestionStateRecovery)
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if c.reno {
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c.congestionWindow = congestion.ByteCount(float64(c.congestionWindow) * renoBeta)
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} else {
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c.congestionWindow = c.cubic.CongestionWindowAfterPacketLoss(c.congestionWindow)
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}
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if minCwnd := c.minCongestionWindow(); c.congestionWindow < minCwnd {
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c.congestionWindow = minCwnd
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}
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c.slowStartThreshold = c.congestionWindow
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c.largestSentAtLastCutback = c.largestSentPacketNumber
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// reset packet count from congestion avoidance mode. We start
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// counting again when we're out of recovery.
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c.numAckedPackets = 0
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}
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// Called when we receive an ack. Normal TCP tracks how many packets one ack
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// represents, but quic has a separate ack for each packet.
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func (c *cubicSender) maybeIncreaseCwnd(
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_ congestion.PacketNumber,
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ackedBytes congestion.ByteCount,
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priorInFlight congestion.ByteCount,
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eventTime time.Time,
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) {
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// Do not increase the congestion window unless the sender is close to using
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// the current window.
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if !c.isCwndLimited(priorInFlight) {
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c.cubic.OnApplicationLimited()
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c.maybeTraceStateChange(logging.CongestionStateApplicationLimited)
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return
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}
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if c.congestionWindow >= c.maxCongestionWindow() {
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return
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}
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if c.InSlowStart() {
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// TCP slow start, exponential growth, increase by one for each ACK.
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c.congestionWindow += c.maxDatagramSize
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c.maybeTraceStateChange(logging.CongestionStateSlowStart)
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return
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}
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// Congestion avoidance
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c.maybeTraceStateChange(logging.CongestionStateCongestionAvoidance)
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if c.reno {
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// Classic Reno congestion avoidance.
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c.numAckedPackets++
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if c.numAckedPackets >= uint64(c.congestionWindow/c.maxDatagramSize) {
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c.congestionWindow += c.maxDatagramSize
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c.numAckedPackets = 0
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}
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} else {
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c.congestionWindow = Min(c.maxCongestionWindow(), c.cubic.CongestionWindowAfterAck(ackedBytes, c.congestionWindow, c.rttStats.MinRTT(), eventTime))
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}
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}
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func (c *cubicSender) isCwndLimited(bytesInFlight congestion.ByteCount) bool {
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congestionWindow := c.GetCongestionWindow()
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if bytesInFlight >= congestionWindow {
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return true
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}
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availableBytes := congestionWindow - bytesInFlight
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slowStartLimited := c.InSlowStart() && bytesInFlight > congestionWindow/2
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return slowStartLimited || availableBytes <= maxBurstPackets*c.maxDatagramSize
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}
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// BandwidthEstimate returns the current bandwidth estimate
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func (c *cubicSender) BandwidthEstimate() Bandwidth {
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if c.rttStats == nil {
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return infBandwidth
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}
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srtt := c.rttStats.SmoothedRTT()
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if srtt == 0 {
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// If we haven't measured an rtt, the bandwidth estimate is unknown.
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return infBandwidth
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}
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return BandwidthFromDelta(c.GetCongestionWindow(), srtt)
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}
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// OnRetransmissionTimeout is called on an retransmission timeout
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func (c *cubicSender) OnRetransmissionTimeout(packetsRetransmitted bool) {
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c.largestSentAtLastCutback = InvalidPacketNumber
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if !packetsRetransmitted {
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return
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}
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c.hybridSlowStart.Restart()
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c.cubic.Reset()
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c.slowStartThreshold = c.congestionWindow / 2
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c.congestionWindow = c.minCongestionWindow()
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}
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// OnConnectionMigration is called when the connection is migrated (?)
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func (c *cubicSender) OnConnectionMigration() {
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c.hybridSlowStart.Restart()
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c.largestSentPacketNumber = InvalidPacketNumber
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c.largestAckedPacketNumber = InvalidPacketNumber
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c.largestSentAtLastCutback = InvalidPacketNumber
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c.lastCutbackExitedSlowstart = false
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c.cubic.Reset()
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c.numAckedPackets = 0
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c.congestionWindow = c.initialCongestionWindow
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c.slowStartThreshold = c.initialMaxCongestionWindow
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}
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func (c *cubicSender) maybeTraceStateChange(new logging.CongestionState) {
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if c.tracer == nil || new == c.lastState {
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return
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}
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c.tracer.UpdatedCongestionState(new)
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c.lastState = new
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}
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func (c *cubicSender) SetMaxDatagramSize(s congestion.ByteCount) {
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if s < c.maxDatagramSize {
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panic(fmt.Sprintf("congestion BUG: decreased max datagram size from %d to %d", c.maxDatagramSize, s))
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}
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cwndIsMinCwnd := c.congestionWindow == c.minCongestionWindow()
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c.maxDatagramSize = s
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if cwndIsMinCwnd {
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c.congestionWindow = c.minCongestionWindow()
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}
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c.pacer.SetMaxDatagramSize(s)
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}
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