1010 lines
33 KiB
Go
1010 lines
33 KiB
Go
package congestion
|
|
|
|
// src from https://quiche.googlesource.com/quiche.git/+/66dea072431f94095dfc3dd2743cb94ef365f7ef/quic/core/congestion_control/bbr_sender.cc
|
|
|
|
import (
|
|
"fmt"
|
|
"math"
|
|
"math/rand"
|
|
"net"
|
|
"time"
|
|
|
|
"github.com/metacubex/quic-go/congestion"
|
|
)
|
|
|
|
const (
|
|
// InitialMaxDatagramSize is the default maximum packet size used in QUIC for congestion window computations in bytes.
|
|
InitialMaxDatagramSize = 1252
|
|
InitialPacketSizeIPv4 = 1252
|
|
InitialPacketSizeIPv6 = 1232
|
|
InitialCongestionWindow = 10
|
|
DefaultBBRMaxCongestionWindow = 10000
|
|
)
|
|
|
|
const (
|
|
initialMinCongestionWindow = 4
|
|
minInitialPacketSize = 1200
|
|
)
|
|
|
|
func GetInitialPacketSize(addr net.Addr) congestion.ByteCount {
|
|
maxSize := congestion.ByteCount(minInitialPacketSize)
|
|
// If this is not a UDP address, we don't know anything about the MTU.
|
|
// Use the minimum size of an Initial packet as the max packet size.
|
|
if udpAddr, ok := addr.(*net.UDPAddr); ok {
|
|
if udpAddr.IP.To4() != nil {
|
|
maxSize = InitialPacketSizeIPv4
|
|
} else {
|
|
maxSize = InitialPacketSizeIPv6
|
|
}
|
|
}
|
|
return maxSize
|
|
}
|
|
|
|
var (
|
|
|
|
// Default initial rtt used before any samples are received.
|
|
InitialRtt = 100 * time.Millisecond
|
|
|
|
// The gain used for the STARTUP, equal to 2/ln(2).
|
|
DefaultHighGain = 2.89
|
|
|
|
// The gain used in STARTUP after loss has been detected.
|
|
// 1.5 is enough to allow for 25% exogenous loss and still observe a 25% growth
|
|
// in measured bandwidth.
|
|
StartupAfterLossGain = 1.5
|
|
|
|
// The cycle of gains used during the PROBE_BW stage.
|
|
PacingGain = []float64{1.25, 0.75, 1, 1, 1, 1, 1, 1}
|
|
|
|
// The length of the gain cycle.
|
|
GainCycleLength = len(PacingGain)
|
|
|
|
// The size of the bandwidth filter window, in round-trips.
|
|
BandwidthWindowSize = GainCycleLength + 2
|
|
|
|
// The time after which the current min_rtt value expires.
|
|
MinRttExpiry = 10 * time.Second
|
|
|
|
// The minimum time the connection can spend in PROBE_RTT mode.
|
|
ProbeRttTime = time.Millisecond * 200
|
|
|
|
// If the bandwidth does not increase by the factor of |kStartupGrowthTarget|
|
|
// within |kRoundTripsWithoutGrowthBeforeExitingStartup| rounds, the connection
|
|
// will exit the STARTUP mode.
|
|
StartupGrowthTarget = 1.25
|
|
RoundTripsWithoutGrowthBeforeExitingStartup = int64(3)
|
|
|
|
// Coefficient of target congestion window to use when basing PROBE_RTT on BDP.
|
|
ModerateProbeRttMultiplier = 0.75
|
|
|
|
// Coefficient to determine if a new RTT is sufficiently similar to min_rtt that
|
|
// we don't need to enter PROBE_RTT.
|
|
SimilarMinRttThreshold = 1.125
|
|
|
|
// Congestion window gain for QUIC BBR during PROBE_BW phase.
|
|
DefaultCongestionWindowGainConst = 2.0
|
|
)
|
|
|
|
type bbrMode int
|
|
|
|
const (
|
|
// Startup phase of the connection.
|
|
STARTUP = iota
|
|
// After achieving the highest possible bandwidth during the startup, lower
|
|
// the pacing rate in order to drain the queue.
|
|
DRAIN
|
|
// Cruising mode.
|
|
PROBE_BW
|
|
// Temporarily slow down sending in order to empty the buffer and measure
|
|
// the real minimum RTT.
|
|
PROBE_RTT
|
|
)
|
|
|
|
type bbrRecoveryState int
|
|
|
|
const (
|
|
// Do not limit.
|
|
NOT_IN_RECOVERY = iota
|
|
|
|
// Allow an extra outstanding byte for each byte acknowledged.
|
|
CONSERVATION
|
|
|
|
// Allow two extra outstanding bytes for each byte acknowledged (slow
|
|
// start).
|
|
GROWTH
|
|
)
|
|
|
|
type bbrSender struct {
|
|
mode bbrMode
|
|
clock Clock
|
|
rttStats congestion.RTTStatsProvider
|
|
bytesInFlight congestion.ByteCount
|
|
// return total bytes of unacked packets.
|
|
//GetBytesInFlight func() congestion.ByteCount
|
|
// Bandwidth sampler provides BBR with the bandwidth measurements at
|
|
// individual points.
|
|
sampler *BandwidthSampler
|
|
// The number of the round trips that have occurred during the connection.
|
|
roundTripCount int64
|
|
// The packet number of the most recently sent packet.
|
|
lastSendPacket congestion.PacketNumber
|
|
// Acknowledgement of any packet after |current_round_trip_end_| will cause
|
|
// the round trip counter to advance.
|
|
currentRoundTripEnd congestion.PacketNumber
|
|
// The filter that tracks the maximum bandwidth over the multiple recent
|
|
// round-trips.
|
|
maxBandwidth *WindowedFilter
|
|
// Tracks the maximum number of bytes acked faster than the sending rate.
|
|
maxAckHeight *WindowedFilter
|
|
// The time this aggregation started and the number of bytes acked during it.
|
|
aggregationEpochStartTime time.Time
|
|
aggregationEpochBytes congestion.ByteCount
|
|
// Minimum RTT estimate. Automatically expires within 10 seconds (and
|
|
// triggers PROBE_RTT mode) if no new value is sampled during that period.
|
|
minRtt time.Duration
|
|
// The time at which the current value of |min_rtt_| was assigned.
|
|
minRttTimestamp time.Time
|
|
// The maximum allowed number of bytes in flight.
|
|
congestionWindow congestion.ByteCount
|
|
// The initial value of the |congestion_window_|.
|
|
initialCongestionWindow congestion.ByteCount
|
|
// The largest value the |congestion_window_| can achieve.
|
|
initialMaxCongestionWindow congestion.ByteCount
|
|
// The smallest value the |congestion_window_| can achieve.
|
|
//minCongestionWindow congestion.ByteCount
|
|
// The pacing gain applied during the STARTUP phase.
|
|
highGain float64
|
|
// The CWND gain applied during the STARTUP phase.
|
|
highCwndGain float64
|
|
// The pacing gain applied during the DRAIN phase.
|
|
drainGain float64
|
|
// The current pacing rate of the connection.
|
|
pacingRate Bandwidth
|
|
// The gain currently applied to the pacing rate.
|
|
pacingGain float64
|
|
// The gain currently applied to the congestion window.
|
|
congestionWindowGain float64
|
|
// The gain used for the congestion window during PROBE_BW. Latched from
|
|
// quic_bbr_cwnd_gain flag.
|
|
congestionWindowGainConst float64
|
|
// The number of RTTs to stay in STARTUP mode. Defaults to 3.
|
|
numStartupRtts int64
|
|
// If true, exit startup if 1RTT has passed with no bandwidth increase and
|
|
// the connection is in recovery.
|
|
exitStartupOnLoss bool
|
|
// Number of round-trips in PROBE_BW mode, used for determining the current
|
|
// pacing gain cycle.
|
|
cycleCurrentOffset int
|
|
// The time at which the last pacing gain cycle was started.
|
|
lastCycleStart time.Time
|
|
// Indicates whether the connection has reached the full bandwidth mode.
|
|
isAtFullBandwidth bool
|
|
// Number of rounds during which there was no significant bandwidth increase.
|
|
roundsWithoutBandwidthGain int64
|
|
// The bandwidth compared to which the increase is measured.
|
|
bandwidthAtLastRound Bandwidth
|
|
// Set to true upon exiting quiescence.
|
|
exitingQuiescence bool
|
|
// Time at which PROBE_RTT has to be exited. Setting it to zero indicates
|
|
// that the time is yet unknown as the number of packets in flight has not
|
|
// reached the required value.
|
|
exitProbeRttAt time.Time
|
|
// Indicates whether a round-trip has passed since PROBE_RTT became active.
|
|
probeRttRoundPassed bool
|
|
// Indicates whether the most recent bandwidth sample was marked as
|
|
// app-limited.
|
|
lastSampleIsAppLimited bool
|
|
// Indicates whether any non app-limited samples have been recorded.
|
|
hasNoAppLimitedSample bool
|
|
// Indicates app-limited calls should be ignored as long as there's
|
|
// enough data inflight to see more bandwidth when necessary.
|
|
flexibleAppLimited bool
|
|
// Current state of recovery.
|
|
recoveryState bbrRecoveryState
|
|
// Receiving acknowledgement of a packet after |end_recovery_at_| will cause
|
|
// BBR to exit the recovery mode. A value above zero indicates at least one
|
|
// loss has been detected, so it must not be set back to zero.
|
|
endRecoveryAt congestion.PacketNumber
|
|
// A window used to limit the number of bytes in flight during loss recovery.
|
|
recoveryWindow congestion.ByteCount
|
|
// If true, consider all samples in recovery app-limited.
|
|
isAppLimitedRecovery bool
|
|
// When true, pace at 1.5x and disable packet conservation in STARTUP.
|
|
slowerStartup bool
|
|
// When true, disables packet conservation in STARTUP.
|
|
rateBasedStartup bool
|
|
// When non-zero, decreases the rate in STARTUP by the total number of bytes
|
|
// lost in STARTUP divided by CWND.
|
|
startupRateReductionMultiplier int64
|
|
// Sum of bytes lost in STARTUP.
|
|
startupBytesLost congestion.ByteCount
|
|
// When true, add the most recent ack aggregation measurement during STARTUP.
|
|
enableAckAggregationDuringStartup bool
|
|
// When true, expire the windowed ack aggregation values in STARTUP when
|
|
// bandwidth increases more than 25%.
|
|
expireAckAggregationInStartup bool
|
|
// If true, will not exit low gain mode until bytes_in_flight drops below BDP
|
|
// or it's time for high gain mode.
|
|
drainToTarget bool
|
|
// If true, use a CWND of 0.75*BDP during probe_rtt instead of 4 packets.
|
|
probeRttBasedOnBdp bool
|
|
// If true, skip probe_rtt and update the timestamp of the existing min_rtt to
|
|
// now if min_rtt over the last cycle is within 12.5% of the current min_rtt.
|
|
// Even if the min_rtt is 12.5% too low, the 25% gain cycling and 2x CWND gain
|
|
// should overcome an overly small min_rtt.
|
|
probeRttSkippedIfSimilarRtt bool
|
|
// If true, disable PROBE_RTT entirely as long as the connection was recently
|
|
// app limited.
|
|
probeRttDisabledIfAppLimited bool
|
|
appLimitedSinceLastProbeRtt bool
|
|
minRttSinceLastProbeRtt time.Duration
|
|
// Latched value of --quic_always_get_bw_sample_when_acked.
|
|
alwaysGetBwSampleWhenAcked bool
|
|
|
|
pacer *pacer
|
|
|
|
maxDatagramSize congestion.ByteCount
|
|
}
|
|
|
|
func NewBBRSender(
|
|
clock Clock,
|
|
initialMaxDatagramSize,
|
|
initialCongestionWindow,
|
|
initialMaxCongestionWindow congestion.ByteCount,
|
|
) *bbrSender {
|
|
b := &bbrSender{
|
|
mode: STARTUP,
|
|
clock: clock,
|
|
sampler: NewBandwidthSampler(),
|
|
maxBandwidth: NewWindowedFilter(int64(BandwidthWindowSize), MaxFilter),
|
|
maxAckHeight: NewWindowedFilter(int64(BandwidthWindowSize), MaxFilter),
|
|
congestionWindow: initialCongestionWindow,
|
|
initialCongestionWindow: initialCongestionWindow,
|
|
highGain: DefaultHighGain,
|
|
highCwndGain: DefaultHighGain,
|
|
drainGain: 1.0 / DefaultHighGain,
|
|
pacingGain: 1.0,
|
|
congestionWindowGain: 1.0,
|
|
congestionWindowGainConst: DefaultCongestionWindowGainConst,
|
|
numStartupRtts: RoundTripsWithoutGrowthBeforeExitingStartup,
|
|
recoveryState: NOT_IN_RECOVERY,
|
|
recoveryWindow: initialMaxCongestionWindow,
|
|
minRttSinceLastProbeRtt: InfiniteRTT,
|
|
maxDatagramSize: initialMaxDatagramSize,
|
|
}
|
|
b.pacer = newPacer(b.BandwidthEstimate)
|
|
return b
|
|
}
|
|
|
|
func (b *bbrSender) maxCongestionWindow() congestion.ByteCount {
|
|
return b.maxDatagramSize * DefaultBBRMaxCongestionWindow
|
|
}
|
|
|
|
func (b *bbrSender) minCongestionWindow() congestion.ByteCount {
|
|
return b.maxDatagramSize * initialMinCongestionWindow
|
|
}
|
|
|
|
func (b *bbrSender) SetRTTStatsProvider(provider congestion.RTTStatsProvider) {
|
|
b.rttStats = provider
|
|
}
|
|
|
|
func (b *bbrSender) GetBytesInFlight() congestion.ByteCount {
|
|
return b.bytesInFlight
|
|
}
|
|
|
|
// TimeUntilSend returns when the next packet should be sent.
|
|
func (b *bbrSender) TimeUntilSend(bytesInFlight congestion.ByteCount) time.Time {
|
|
b.bytesInFlight = bytesInFlight
|
|
return b.pacer.TimeUntilSend()
|
|
}
|
|
|
|
func (b *bbrSender) HasPacingBudget() bool {
|
|
return b.pacer.Budget(b.clock.Now()) >= b.maxDatagramSize
|
|
}
|
|
|
|
func (b *bbrSender) SetMaxDatagramSize(s congestion.ByteCount) {
|
|
if s < b.maxDatagramSize {
|
|
panic(fmt.Sprintf("congestion BUG: decreased max datagram size from %d to %d", b.maxDatagramSize, s))
|
|
}
|
|
cwndIsMinCwnd := b.congestionWindow == b.minCongestionWindow()
|
|
b.maxDatagramSize = s
|
|
if cwndIsMinCwnd {
|
|
b.congestionWindow = b.minCongestionWindow()
|
|
}
|
|
b.pacer.SetMaxDatagramSize(s)
|
|
}
|
|
|
|
func (b *bbrSender) OnPacketSent(sentTime time.Time, bytesInFlight congestion.ByteCount, packetNumber congestion.PacketNumber, bytes congestion.ByteCount, isRetransmittable bool) {
|
|
b.pacer.SentPacket(sentTime, bytes)
|
|
b.lastSendPacket = packetNumber
|
|
|
|
b.bytesInFlight = bytesInFlight
|
|
if bytesInFlight == 0 && b.sampler.isAppLimited {
|
|
b.exitingQuiescence = true
|
|
}
|
|
|
|
if b.aggregationEpochStartTime.IsZero() {
|
|
b.aggregationEpochStartTime = sentTime
|
|
}
|
|
|
|
b.sampler.OnPacketSent(sentTime, packetNumber, bytes, bytesInFlight, isRetransmittable)
|
|
}
|
|
|
|
func (b *bbrSender) CanSend(bytesInFlight congestion.ByteCount) bool {
|
|
b.bytesInFlight = bytesInFlight
|
|
return bytesInFlight < b.GetCongestionWindow()
|
|
}
|
|
|
|
func (b *bbrSender) GetCongestionWindow() congestion.ByteCount {
|
|
if b.mode == PROBE_RTT {
|
|
return b.ProbeRttCongestionWindow()
|
|
}
|
|
|
|
if b.InRecovery() && !(b.rateBasedStartup && b.mode == STARTUP) {
|
|
return minByteCount(b.congestionWindow, b.recoveryWindow)
|
|
}
|
|
|
|
return b.congestionWindow
|
|
}
|
|
|
|
func (b *bbrSender) MaybeExitSlowStart() {
|
|
|
|
}
|
|
|
|
func (b *bbrSender) OnPacketAcked(number congestion.PacketNumber, ackedBytes congestion.ByteCount, priorInFlight congestion.ByteCount, eventTime time.Time) {
|
|
totalBytesAckedBefore := b.sampler.totalBytesAcked
|
|
isRoundStart, minRttExpired := false, false
|
|
lastAckedPacket := number
|
|
|
|
isRoundStart = b.UpdateRoundTripCounter(lastAckedPacket)
|
|
minRttExpired = b.UpdateBandwidthAndMinRtt(eventTime, number, ackedBytes)
|
|
b.UpdateRecoveryState(false, isRoundStart)
|
|
bytesAcked := b.sampler.totalBytesAcked - totalBytesAckedBefore
|
|
excessAcked := b.UpdateAckAggregationBytes(eventTime, bytesAcked)
|
|
|
|
// Handle logic specific to STARTUP and DRAIN modes.
|
|
if isRoundStart && !b.isAtFullBandwidth {
|
|
b.CheckIfFullBandwidthReached()
|
|
}
|
|
b.MaybeExitStartupOrDrain(eventTime)
|
|
|
|
// Handle logic specific to PROBE_RTT.
|
|
b.MaybeEnterOrExitProbeRtt(eventTime, isRoundStart, minRttExpired)
|
|
|
|
// After the model is updated, recalculate the pacing rate and congestion
|
|
// window.
|
|
b.CalculatePacingRate()
|
|
b.CalculateCongestionWindow(bytesAcked, excessAcked)
|
|
b.CalculateRecoveryWindow(bytesAcked, congestion.ByteCount(0))
|
|
|
|
}
|
|
|
|
func (b *bbrSender) OnPacketLost(number congestion.PacketNumber, lostBytes congestion.ByteCount, priorInFlight congestion.ByteCount) {
|
|
eventTime := time.Now()
|
|
totalBytesAckedBefore := b.sampler.totalBytesAcked
|
|
isRoundStart, minRttExpired := false, false
|
|
|
|
b.DiscardLostPackets(number, lostBytes)
|
|
|
|
// Input the new data into the BBR model of the connection.
|
|
var excessAcked congestion.ByteCount
|
|
|
|
// Handle logic specific to PROBE_BW mode.
|
|
if b.mode == PROBE_BW {
|
|
b.UpdateGainCyclePhase(time.Now(), priorInFlight, true)
|
|
}
|
|
|
|
// Handle logic specific to STARTUP and DRAIN modes.
|
|
b.MaybeExitStartupOrDrain(eventTime)
|
|
|
|
// Handle logic specific to PROBE_RTT.
|
|
b.MaybeEnterOrExitProbeRtt(eventTime, isRoundStart, minRttExpired)
|
|
|
|
// Calculate number of packets acked and lost.
|
|
bytesAcked := b.sampler.totalBytesAcked - totalBytesAckedBefore
|
|
bytesLost := lostBytes
|
|
|
|
// After the model is updated, recalculate the pacing rate and congestion
|
|
// window.
|
|
b.CalculatePacingRate()
|
|
b.CalculateCongestionWindow(bytesAcked, excessAcked)
|
|
b.CalculateRecoveryWindow(bytesAcked, bytesLost)
|
|
}
|
|
|
|
//func (b *bbrSender) OnCongestionEvent(priorInFlight congestion.ByteCount, eventTime time.Time, ackedPackets, lostPackets []*congestion.Packet) {
|
|
// totalBytesAckedBefore := b.sampler.totalBytesAcked
|
|
// isRoundStart, minRttExpired := false, false
|
|
//
|
|
// if lostPackets != nil {
|
|
// b.DiscardLostPackets(lostPackets)
|
|
// }
|
|
//
|
|
// // Input the new data into the BBR model of the connection.
|
|
// var excessAcked congestion.ByteCount
|
|
// if len(ackedPackets) > 0 {
|
|
// lastAckedPacket := ackedPackets[len(ackedPackets)-1].PacketNumber
|
|
// isRoundStart = b.UpdateRoundTripCounter(lastAckedPacket)
|
|
// minRttExpired = b.UpdateBandwidthAndMinRtt(eventTime, ackedPackets)
|
|
// b.UpdateRecoveryState(lastAckedPacket, len(lostPackets) > 0, isRoundStart)
|
|
// bytesAcked := b.sampler.totalBytesAcked - totalBytesAckedBefore
|
|
// excessAcked = b.UpdateAckAggregationBytes(eventTime, bytesAcked)
|
|
// }
|
|
//
|
|
// // Handle logic specific to PROBE_BW mode.
|
|
// if b.mode == PROBE_BW {
|
|
// b.UpdateGainCyclePhase(eventTime, priorInFlight, len(lostPackets) > 0)
|
|
// }
|
|
//
|
|
// // Handle logic specific to STARTUP and DRAIN modes.
|
|
// if isRoundStart && !b.isAtFullBandwidth {
|
|
// b.CheckIfFullBandwidthReached()
|
|
// }
|
|
// b.MaybeExitStartupOrDrain(eventTime)
|
|
//
|
|
// // Handle logic specific to PROBE_RTT.
|
|
// b.MaybeEnterOrExitProbeRtt(eventTime, isRoundStart, minRttExpired)
|
|
//
|
|
// // Calculate number of packets acked and lost.
|
|
// bytesAcked := b.sampler.totalBytesAcked - totalBytesAckedBefore
|
|
// bytesLost := congestion.ByteCount(0)
|
|
// for _, packet := range lostPackets {
|
|
// bytesLost += packet.Length
|
|
// }
|
|
//
|
|
// // After the model is updated, recalculate the pacing rate and congestion
|
|
// // window.
|
|
// b.CalculatePacingRate()
|
|
// b.CalculateCongestionWindow(bytesAcked, excessAcked)
|
|
// b.CalculateRecoveryWindow(bytesAcked, bytesLost)
|
|
//}
|
|
|
|
//func (b *bbrSender) SetNumEmulatedConnections(n int) {
|
|
//
|
|
//}
|
|
|
|
func (b *bbrSender) OnRetransmissionTimeout(packetsRetransmitted bool) {
|
|
|
|
}
|
|
|
|
//func (b *bbrSender) OnConnectionMigration() {
|
|
//
|
|
//}
|
|
|
|
//// Experiments
|
|
//func (b *bbrSender) SetSlowStartLargeReduction(enabled bool) {
|
|
//
|
|
//}
|
|
|
|
//func (b *bbrSender) BandwidthEstimate() Bandwidth {
|
|
// return Bandwidth(b.maxBandwidth.GetBest())
|
|
//}
|
|
|
|
// BandwidthEstimate returns the current bandwidth estimate
|
|
func (b *bbrSender) BandwidthEstimate() Bandwidth {
|
|
if b.rttStats == nil {
|
|
return infBandwidth
|
|
}
|
|
srtt := b.rttStats.SmoothedRTT()
|
|
if srtt == 0 {
|
|
// If we haven't measured an rtt, the bandwidth estimate is unknown.
|
|
return infBandwidth
|
|
}
|
|
return BandwidthFromDelta(b.GetCongestionWindow(), srtt)
|
|
}
|
|
|
|
//func (b *bbrSender) HybridSlowStart() *HybridSlowStart {
|
|
// return nil
|
|
//}
|
|
|
|
//func (b *bbrSender) SlowstartThreshold() congestion.ByteCount {
|
|
// return 0
|
|
//}
|
|
|
|
//func (b *bbrSender) RenoBeta() float32 {
|
|
// return 0.0
|
|
//}
|
|
|
|
func (b *bbrSender) InRecovery() bool {
|
|
return b.recoveryState != NOT_IN_RECOVERY
|
|
}
|
|
|
|
func (b *bbrSender) InSlowStart() bool {
|
|
return b.mode == STARTUP
|
|
}
|
|
|
|
//func (b *bbrSender) ShouldSendProbingPacket() bool {
|
|
// if b.pacingGain <= 1 {
|
|
// return false
|
|
// }
|
|
// // TODO(b/77975811): If the pipe is highly under-utilized, consider not
|
|
// // sending a probing transmission, because the extra bandwidth is not needed.
|
|
// // If flexible_app_limited is enabled, check if the pipe is sufficiently full.
|
|
// if b.flexibleAppLimited {
|
|
// return !b.IsPipeSufficientlyFull()
|
|
// } else {
|
|
// return true
|
|
// }
|
|
//}
|
|
|
|
//func (b *bbrSender) IsPipeSufficientlyFull() bool {
|
|
// // See if we need more bytes in flight to see more bandwidth.
|
|
// if b.mode == STARTUP {
|
|
// // STARTUP exits if it doesn't observe a 25% bandwidth increase, so the CWND
|
|
// // must be more than 25% above the target.
|
|
// return b.GetBytesInFlight() >= b.GetTargetCongestionWindow(1.5)
|
|
// }
|
|
// if b.pacingGain > 1 {
|
|
// // Super-unity PROBE_BW doesn't exit until 1.25 * BDP is achieved.
|
|
// return b.GetBytesInFlight() >= b.GetTargetCongestionWindow(b.pacingGain)
|
|
// }
|
|
// // If bytes_in_flight are above the target congestion window, it should be
|
|
// // possible to observe the same or more bandwidth if it's available.
|
|
// return b.GetBytesInFlight() >= b.GetTargetCongestionWindow(1.1)
|
|
//}
|
|
|
|
//func (b *bbrSender) SetFromConfig() {
|
|
// // TODO: not impl.
|
|
//}
|
|
|
|
func (b *bbrSender) UpdateRoundTripCounter(lastAckedPacket congestion.PacketNumber) bool {
|
|
if b.currentRoundTripEnd == 0 || lastAckedPacket > b.currentRoundTripEnd {
|
|
b.currentRoundTripEnd = lastAckedPacket
|
|
b.roundTripCount++
|
|
// if b.rttStats != nil && b.InSlowStart() {
|
|
// TODO: ++stats_->slowstart_num_rtts;
|
|
// }
|
|
return true
|
|
}
|
|
return false
|
|
}
|
|
|
|
func (b *bbrSender) UpdateBandwidthAndMinRtt(now time.Time, number congestion.PacketNumber, ackedBytes congestion.ByteCount) bool {
|
|
sampleMinRtt := InfiniteRTT
|
|
|
|
if !b.alwaysGetBwSampleWhenAcked && ackedBytes == 0 {
|
|
// Skip acked packets with 0 in flight bytes when updating bandwidth.
|
|
return false
|
|
}
|
|
bandwidthSample := b.sampler.OnPacketAcked(now, number)
|
|
if b.alwaysGetBwSampleWhenAcked && !bandwidthSample.stateAtSend.isValid {
|
|
// From the sampler's perspective, the packet has never been sent, or the
|
|
// packet has been acked or marked as lost previously.
|
|
return false
|
|
}
|
|
b.lastSampleIsAppLimited = bandwidthSample.stateAtSend.isAppLimited
|
|
// has_non_app_limited_sample_ |=
|
|
// !bandwidth_sample.state_at_send.is_app_limited;
|
|
if !bandwidthSample.stateAtSend.isAppLimited {
|
|
b.hasNoAppLimitedSample = true
|
|
}
|
|
if bandwidthSample.rtt > 0 {
|
|
sampleMinRtt = minRtt(sampleMinRtt, bandwidthSample.rtt)
|
|
}
|
|
if !bandwidthSample.stateAtSend.isAppLimited || bandwidthSample.bandwidth > b.BandwidthEstimate() {
|
|
b.maxBandwidth.Update(int64(bandwidthSample.bandwidth), b.roundTripCount)
|
|
}
|
|
|
|
// If none of the RTT samples are valid, return immediately.
|
|
if sampleMinRtt == InfiniteRTT {
|
|
return false
|
|
}
|
|
|
|
b.minRttSinceLastProbeRtt = minRtt(b.minRttSinceLastProbeRtt, sampleMinRtt)
|
|
// Do not expire min_rtt if none was ever available.
|
|
minRttExpired := b.minRtt > 0 && (now.After(b.minRttTimestamp.Add(MinRttExpiry)))
|
|
if minRttExpired || sampleMinRtt < b.minRtt || b.minRtt == 0 {
|
|
if minRttExpired && b.ShouldExtendMinRttExpiry() {
|
|
minRttExpired = false
|
|
} else {
|
|
b.minRtt = sampleMinRtt
|
|
}
|
|
b.minRttTimestamp = now
|
|
// Reset since_last_probe_rtt fields.
|
|
b.minRttSinceLastProbeRtt = InfiniteRTT
|
|
b.appLimitedSinceLastProbeRtt = false
|
|
}
|
|
|
|
return minRttExpired
|
|
}
|
|
|
|
func (b *bbrSender) ShouldExtendMinRttExpiry() bool {
|
|
if b.probeRttDisabledIfAppLimited && b.appLimitedSinceLastProbeRtt {
|
|
// Extend the current min_rtt if we've been app limited recently.
|
|
return true
|
|
}
|
|
|
|
minRttIncreasedSinceLastProbe := b.minRttSinceLastProbeRtt > time.Duration(float64(b.minRtt)*SimilarMinRttThreshold)
|
|
if b.probeRttSkippedIfSimilarRtt && b.appLimitedSinceLastProbeRtt && !minRttIncreasedSinceLastProbe {
|
|
// Extend the current min_rtt if we've been app limited recently and an rtt
|
|
// has been measured in that time that's less than 12.5% more than the
|
|
// current min_rtt.
|
|
return true
|
|
}
|
|
|
|
return false
|
|
}
|
|
|
|
func (b *bbrSender) DiscardLostPackets(number congestion.PacketNumber, lostBytes congestion.ByteCount) {
|
|
b.sampler.OnPacketLost(number)
|
|
if b.mode == STARTUP {
|
|
// if b.rttStats != nil {
|
|
// TODO: slow start.
|
|
// }
|
|
if b.startupRateReductionMultiplier != 0 {
|
|
b.startupBytesLost += lostBytes
|
|
}
|
|
}
|
|
}
|
|
|
|
func (b *bbrSender) UpdateRecoveryState(hasLosses, isRoundStart bool) {
|
|
// Exit recovery when there are no losses for a round.
|
|
if !hasLosses {
|
|
b.endRecoveryAt = b.lastSendPacket
|
|
}
|
|
switch b.recoveryState {
|
|
case NOT_IN_RECOVERY:
|
|
// Enter conservation on the first loss.
|
|
if hasLosses {
|
|
b.recoveryState = CONSERVATION
|
|
// This will cause the |recovery_window_| to be set to the correct
|
|
// value in CalculateRecoveryWindow().
|
|
b.recoveryWindow = 0
|
|
// Since the conservation phase is meant to be lasting for a whole
|
|
// round, extend the current round as if it were started right now.
|
|
b.currentRoundTripEnd = b.lastSendPacket
|
|
if false && b.lastSampleIsAppLimited {
|
|
b.isAppLimitedRecovery = true
|
|
}
|
|
}
|
|
case CONSERVATION:
|
|
if isRoundStart {
|
|
b.recoveryState = GROWTH
|
|
}
|
|
fallthrough
|
|
case GROWTH:
|
|
// Exit recovery if appropriate.
|
|
if !hasLosses && b.lastSendPacket > b.endRecoveryAt {
|
|
b.recoveryState = NOT_IN_RECOVERY
|
|
b.isAppLimitedRecovery = false
|
|
}
|
|
}
|
|
|
|
if b.recoveryState != NOT_IN_RECOVERY && b.isAppLimitedRecovery {
|
|
b.sampler.OnAppLimited()
|
|
}
|
|
}
|
|
|
|
func (b *bbrSender) UpdateAckAggregationBytes(ackTime time.Time, ackedBytes congestion.ByteCount) congestion.ByteCount {
|
|
// Compute how many bytes are expected to be delivered, assuming max bandwidth
|
|
// is correct.
|
|
expectedAckedBytes := congestion.ByteCount(b.maxBandwidth.GetBest()) *
|
|
congestion.ByteCount((ackTime.Sub(b.aggregationEpochStartTime)))
|
|
// Reset the current aggregation epoch as soon as the ack arrival rate is less
|
|
// than or equal to the max bandwidth.
|
|
if b.aggregationEpochBytes <= expectedAckedBytes {
|
|
// Reset to start measuring a new aggregation epoch.
|
|
b.aggregationEpochBytes = ackedBytes
|
|
b.aggregationEpochStartTime = ackTime
|
|
return 0
|
|
}
|
|
// Compute how many extra bytes were delivered vs max bandwidth.
|
|
// Include the bytes most recently acknowledged to account for stretch acks.
|
|
b.aggregationEpochBytes += ackedBytes
|
|
b.maxAckHeight.Update(int64(b.aggregationEpochBytes-expectedAckedBytes), b.roundTripCount)
|
|
return b.aggregationEpochBytes - expectedAckedBytes
|
|
}
|
|
|
|
func (b *bbrSender) UpdateGainCyclePhase(now time.Time, priorInFlight congestion.ByteCount, hasLosses bool) {
|
|
bytesInFlight := b.GetBytesInFlight()
|
|
// In most cases, the cycle is advanced after an RTT passes.
|
|
shouldAdvanceGainCycling := now.Sub(b.lastCycleStart) > b.GetMinRtt()
|
|
|
|
// If the pacing gain is above 1.0, the connection is trying to probe the
|
|
// bandwidth by increasing the number of bytes in flight to at least
|
|
// pacing_gain * BDP. Make sure that it actually reaches the target, as long
|
|
// as there are no losses suggesting that the buffers are not able to hold
|
|
// that much.
|
|
if b.pacingGain > 1.0 && !hasLosses && priorInFlight < b.GetTargetCongestionWindow(b.pacingGain) {
|
|
shouldAdvanceGainCycling = false
|
|
}
|
|
// If pacing gain is below 1.0, the connection is trying to drain the extra
|
|
// queue which could have been incurred by probing prior to it. If the number
|
|
// of bytes in flight falls down to the estimated BDP value earlier, conclude
|
|
// that the queue has been successfully drained and exit this cycle early.
|
|
if b.pacingGain < 1.0 && bytesInFlight <= b.GetTargetCongestionWindow(1.0) {
|
|
shouldAdvanceGainCycling = true
|
|
}
|
|
|
|
if shouldAdvanceGainCycling {
|
|
b.cycleCurrentOffset = (b.cycleCurrentOffset + 1) % GainCycleLength
|
|
b.lastCycleStart = now
|
|
// Stay in low gain mode until the target BDP is hit.
|
|
// Low gain mode will be exited immediately when the target BDP is achieved.
|
|
if b.drainToTarget && b.pacingGain < 1.0 && PacingGain[b.cycleCurrentOffset] == 1.0 &&
|
|
bytesInFlight > b.GetTargetCongestionWindow(1.0) {
|
|
return
|
|
}
|
|
b.pacingGain = PacingGain[b.cycleCurrentOffset]
|
|
}
|
|
}
|
|
|
|
func (b *bbrSender) GetTargetCongestionWindow(gain float64) congestion.ByteCount {
|
|
bdp := congestion.ByteCount(b.GetMinRtt()) * congestion.ByteCount(b.BandwidthEstimate())
|
|
congestionWindow := congestion.ByteCount(gain * float64(bdp))
|
|
|
|
// BDP estimate will be zero if no bandwidth samples are available yet.
|
|
if congestionWindow == 0 {
|
|
congestionWindow = congestion.ByteCount(gain * float64(b.initialCongestionWindow))
|
|
}
|
|
|
|
return maxByteCount(congestionWindow, b.minCongestionWindow())
|
|
}
|
|
|
|
func (b *bbrSender) CheckIfFullBandwidthReached() {
|
|
if b.lastSampleIsAppLimited {
|
|
return
|
|
}
|
|
|
|
target := Bandwidth(float64(b.bandwidthAtLastRound) * StartupGrowthTarget)
|
|
if b.BandwidthEstimate() >= target {
|
|
b.bandwidthAtLastRound = b.BandwidthEstimate()
|
|
b.roundsWithoutBandwidthGain = 0
|
|
if b.expireAckAggregationInStartup {
|
|
// Expire old excess delivery measurements now that bandwidth increased.
|
|
b.maxAckHeight.Reset(0, b.roundTripCount)
|
|
}
|
|
return
|
|
}
|
|
b.roundsWithoutBandwidthGain++
|
|
if b.roundsWithoutBandwidthGain >= b.numStartupRtts || (b.exitStartupOnLoss && b.InRecovery()) {
|
|
b.isAtFullBandwidth = true
|
|
}
|
|
}
|
|
|
|
func (b *bbrSender) MaybeExitStartupOrDrain(now time.Time) {
|
|
if b.mode == STARTUP && b.isAtFullBandwidth {
|
|
b.OnExitStartup(now)
|
|
b.mode = DRAIN
|
|
b.pacingGain = b.drainGain
|
|
b.congestionWindowGain = b.highCwndGain
|
|
}
|
|
if b.mode == DRAIN && b.GetBytesInFlight() <= b.GetTargetCongestionWindow(1) {
|
|
b.EnterProbeBandwidthMode(now)
|
|
}
|
|
}
|
|
|
|
func (b *bbrSender) EnterProbeBandwidthMode(now time.Time) {
|
|
b.mode = PROBE_BW
|
|
b.congestionWindowGain = b.congestionWindowGainConst
|
|
|
|
// Pick a random offset for the gain cycle out of {0, 2..7} range. 1 is
|
|
// excluded because in that case increased gain and decreased gain would not
|
|
// follow each other.
|
|
b.cycleCurrentOffset = rand.Int() % (GainCycleLength - 1)
|
|
if b.cycleCurrentOffset >= 1 {
|
|
b.cycleCurrentOffset += 1
|
|
}
|
|
|
|
b.lastCycleStart = now
|
|
b.pacingGain = PacingGain[b.cycleCurrentOffset]
|
|
}
|
|
|
|
func (b *bbrSender) MaybeEnterOrExitProbeRtt(now time.Time, isRoundStart, minRttExpired bool) {
|
|
if minRttExpired && !b.exitingQuiescence && b.mode != PROBE_RTT {
|
|
if b.InSlowStart() {
|
|
b.OnExitStartup(now)
|
|
}
|
|
b.mode = PROBE_RTT
|
|
b.pacingGain = 1.0
|
|
// Do not decide on the time to exit PROBE_RTT until the |bytes_in_flight|
|
|
// is at the target small value.
|
|
b.exitProbeRttAt = time.Time{}
|
|
}
|
|
|
|
if b.mode == PROBE_RTT {
|
|
b.sampler.OnAppLimited()
|
|
if b.exitProbeRttAt.IsZero() {
|
|
// If the window has reached the appropriate size, schedule exiting
|
|
// PROBE_RTT. The CWND during PROBE_RTT is kMinimumCongestionWindow, but
|
|
// we allow an extra packet since QUIC checks CWND before sending a
|
|
// packet.
|
|
if b.GetBytesInFlight() < b.ProbeRttCongestionWindow()+b.maxDatagramSize {
|
|
b.exitProbeRttAt = now.Add(ProbeRttTime)
|
|
b.probeRttRoundPassed = false
|
|
}
|
|
} else {
|
|
if isRoundStart {
|
|
b.probeRttRoundPassed = true
|
|
}
|
|
if !now.Before(b.exitProbeRttAt) && b.probeRttRoundPassed {
|
|
b.minRttTimestamp = now
|
|
if !b.isAtFullBandwidth {
|
|
b.EnterStartupMode(now)
|
|
} else {
|
|
b.EnterProbeBandwidthMode(now)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
b.exitingQuiescence = false
|
|
}
|
|
|
|
func (b *bbrSender) ProbeRttCongestionWindow() congestion.ByteCount {
|
|
if b.probeRttBasedOnBdp {
|
|
return b.GetTargetCongestionWindow(ModerateProbeRttMultiplier)
|
|
} else {
|
|
return b.minCongestionWindow()
|
|
}
|
|
}
|
|
|
|
func (b *bbrSender) EnterStartupMode(now time.Time) {
|
|
// if b.rttStats != nil {
|
|
// TODO: slow start.
|
|
// }
|
|
b.mode = STARTUP
|
|
b.pacingGain = b.highGain
|
|
b.congestionWindowGain = b.highCwndGain
|
|
}
|
|
|
|
func (b *bbrSender) OnExitStartup(now time.Time) {
|
|
if b.rttStats == nil {
|
|
return
|
|
}
|
|
// TODO: slow start.
|
|
}
|
|
|
|
func (b *bbrSender) CalculatePacingRate() {
|
|
if b.BandwidthEstimate() == 0 {
|
|
return
|
|
}
|
|
|
|
targetRate := Bandwidth(b.pacingGain * float64(b.BandwidthEstimate()))
|
|
if b.isAtFullBandwidth {
|
|
b.pacingRate = targetRate
|
|
return
|
|
}
|
|
|
|
// Pace at the rate of initial_window / RTT as soon as RTT measurements are
|
|
// available.
|
|
if b.pacingRate == 0 && b.rttStats.MinRTT() > 0 {
|
|
b.pacingRate = BandwidthFromDelta(b.initialCongestionWindow, b.rttStats.MinRTT())
|
|
return
|
|
}
|
|
// Slow the pacing rate in STARTUP once loss has ever been detected.
|
|
hasEverDetectedLoss := b.endRecoveryAt > 0
|
|
if b.slowerStartup && hasEverDetectedLoss && b.hasNoAppLimitedSample {
|
|
b.pacingRate = Bandwidth(StartupAfterLossGain * float64(b.BandwidthEstimate()))
|
|
return
|
|
}
|
|
|
|
// Slow the pacing rate in STARTUP by the bytes_lost / CWND.
|
|
if b.startupRateReductionMultiplier != 0 && hasEverDetectedLoss && b.hasNoAppLimitedSample {
|
|
b.pacingRate = Bandwidth((1.0 - (float64(b.startupBytesLost) * float64(b.startupRateReductionMultiplier) / float64(b.congestionWindow))) * float64(targetRate))
|
|
// Ensure the pacing rate doesn't drop below the startup growth target times
|
|
// the bandwidth estimate.
|
|
b.pacingRate = maxBandwidth(b.pacingRate, Bandwidth(StartupGrowthTarget*float64(b.BandwidthEstimate())))
|
|
return
|
|
}
|
|
|
|
// Do not decrease the pacing rate during startup.
|
|
b.pacingRate = maxBandwidth(b.pacingRate, targetRate)
|
|
}
|
|
|
|
func (b *bbrSender) CalculateCongestionWindow(ackedBytes, excessAcked congestion.ByteCount) {
|
|
if b.mode == PROBE_RTT {
|
|
return
|
|
}
|
|
|
|
targetWindow := b.GetTargetCongestionWindow(b.congestionWindowGain)
|
|
if b.isAtFullBandwidth {
|
|
// Add the max recently measured ack aggregation to CWND.
|
|
targetWindow += congestion.ByteCount(b.maxAckHeight.GetBest())
|
|
} else if b.enableAckAggregationDuringStartup {
|
|
// Add the most recent excess acked. Because CWND never decreases in
|
|
// STARTUP, this will automatically create a very localized max filter.
|
|
targetWindow += excessAcked
|
|
}
|
|
|
|
// Instead of immediately setting the target CWND as the new one, BBR grows
|
|
// the CWND towards |target_window| by only increasing it |bytes_acked| at a
|
|
// time.
|
|
addBytesAcked := true || !b.InRecovery()
|
|
if b.isAtFullBandwidth {
|
|
b.congestionWindow = minByteCount(targetWindow, b.congestionWindow+ackedBytes)
|
|
} else if addBytesAcked && (b.congestionWindow < targetWindow || b.sampler.totalBytesAcked < b.initialCongestionWindow) {
|
|
// If the connection is not yet out of startup phase, do not decrease the
|
|
// window.
|
|
b.congestionWindow += ackedBytes
|
|
}
|
|
|
|
// Enforce the limits on the congestion window.
|
|
b.congestionWindow = maxByteCount(b.congestionWindow, b.minCongestionWindow())
|
|
b.congestionWindow = minByteCount(b.congestionWindow, b.maxCongestionWindow())
|
|
}
|
|
|
|
func (b *bbrSender) CalculateRecoveryWindow(ackedBytes, lostBytes congestion.ByteCount) {
|
|
if b.rateBasedStartup && b.mode == STARTUP {
|
|
return
|
|
}
|
|
|
|
if b.recoveryState == NOT_IN_RECOVERY {
|
|
return
|
|
}
|
|
|
|
// Set up the initial recovery window.
|
|
if b.recoveryWindow == 0 {
|
|
b.recoveryWindow = maxByteCount(b.GetBytesInFlight()+ackedBytes, b.minCongestionWindow())
|
|
return
|
|
}
|
|
|
|
// Remove losses from the recovery window, while accounting for a potential
|
|
// integer underflow.
|
|
if b.recoveryWindow >= lostBytes {
|
|
b.recoveryWindow -= lostBytes
|
|
} else {
|
|
b.recoveryWindow = congestion.ByteCount(b.maxDatagramSize)
|
|
}
|
|
// In CONSERVATION mode, just subtracting losses is sufficient. In GROWTH,
|
|
// release additional |bytes_acked| to achieve a slow-start-like behavior.
|
|
if b.recoveryState == GROWTH {
|
|
b.recoveryWindow += ackedBytes
|
|
}
|
|
// Sanity checks. Ensure that we always allow to send at least an MSS or
|
|
// |bytes_acked| in response, whichever is larger.
|
|
b.recoveryWindow = maxByteCount(b.recoveryWindow, b.GetBytesInFlight()+ackedBytes)
|
|
b.recoveryWindow = maxByteCount(b.recoveryWindow, b.minCongestionWindow())
|
|
}
|
|
|
|
var _ congestion.CongestionControl = &bbrSender{}
|
|
|
|
func (b *bbrSender) GetMinRtt() time.Duration {
|
|
if b.minRtt > 0 {
|
|
return b.minRtt
|
|
} else {
|
|
return InitialRtt
|
|
}
|
|
}
|
|
|
|
func minRtt(a, b time.Duration) time.Duration {
|
|
if a < b {
|
|
return a
|
|
} else {
|
|
return b
|
|
}
|
|
}
|
|
|
|
func minBandwidth(a, b Bandwidth) Bandwidth {
|
|
if a < b {
|
|
return a
|
|
} else {
|
|
return b
|
|
}
|
|
}
|
|
|
|
func maxBandwidth(a, b Bandwidth) Bandwidth {
|
|
if a > b {
|
|
return a
|
|
} else {
|
|
return b
|
|
}
|
|
}
|
|
|
|
func maxByteCount(a, b congestion.ByteCount) congestion.ByteCount {
|
|
if a > b {
|
|
return a
|
|
} else {
|
|
return b
|
|
}
|
|
}
|
|
|
|
func minByteCount(a, b congestion.ByteCount) congestion.ByteCount {
|
|
if a < b {
|
|
return a
|
|
} else {
|
|
return b
|
|
}
|
|
}
|
|
|
|
var (
|
|
InfiniteRTT = time.Duration(math.MaxInt64)
|
|
)
|