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SwiftQUIC: PERF: Move CongestionControl state to a common struct #204

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SwiftQUIC: PERF: Move CongestionControl state to a common struct
agnosticdev Oct 1, 2026
bd24fc3
Merge branch 'main' into agnosticdev/CongestionControl
agnosticdev Oct 3, 2026
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806 changes: 395 additions & 411 deletions Sources/SwiftNetwork/QUIC/CongestionControl.swift
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250 changes: 123 additions & 127 deletions Sources/SwiftNetwork/QUIC/Cubic.swift
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199 changes: 93 additions & 106 deletions Sources/SwiftNetwork/QUIC/Ledbat.swift
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299 changes: 145 additions & 154 deletions Sources/SwiftNetwork/QUIC/Prague.swift
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138 changes: 79 additions & 59 deletions Sources/SwiftNetwork/QUIC/QUICPath.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -156,7 +156,7 @@ public final class QUICPath: MultiplexingDatagramPath<

var bdp = BandwidthDelayProduct()

private var congestionControl: CongestionControl?
private var congestionControl: CongestionControl

var pacer: Pacer

Expand Down Expand Up @@ -337,6 +337,14 @@ public final class QUICPath: MultiplexingDatagramPath<
required init(parent: QUICConnection, in eventContext: inout NetworkContext.EventContext) {
self.rtt = RTT(logPrefixer: parent.logPrefixer)
self.pacer = Pacer()
// Overwritten with the real mss/qlog once `setup()` runs; RX/TX aren't allowed on a
// path until then, so this placeholder is never observed.
self.congestionControl = CongestionControl.createCubic(
pacer: &self.pacer,
mss: 0,
qlog: nil,
logPrefixer: parent.logPrefixer
)
super.init(parent: parent, in: &eventContext)
}

Expand Down Expand Up @@ -371,13 +379,11 @@ public final class QUICPath: MultiplexingDatagramPath<

let pacerEnabled = (pacePackets || QUICPreferences.shared.pacePackets)
self.pacer = Pacer(enabled: pacerEnabled)
self.congestionControl = .cubic(
algorithm: Cubic(
pacer: &self.pacer,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
self.congestionControl = .createCubic(
pacer: &self.pacer,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)

self.spinValue = parentProtocol.initialSpinValue
Expand Down Expand Up @@ -438,42 +444,34 @@ public final class QUICPath: MultiplexingDatagramPath<
}

func resetCongestionControl() {
switch self.congestionControl {
switch self.congestionControl.algorithm {
case .cubic:
self.congestionControl = .cubic(
algorithm: Cubic(
pacer: &self.pacer,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
self.congestionControl = .createCubic(
pacer: &self.pacer,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
#if !NETWORK_EMBEDDED
case .ledbat:
self.congestionControl = .ledbat(
algorithm: Ledbat(
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
self.congestionControl = .createLedbat(
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
case .prague:
self.congestionControl = .prague(
algorithm: Prague(
pacer: &self.pacer,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
self.congestionControl = .createPrague(
pacer: &self.pacer,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
#endif
case .none:
break
}
}

func idleTimeoutCongestionControl() {
self.congestionControl?.idleTimeout(mss: mss)
self.congestionControl.idleTimeout(mss: mss)
}

func setupL4SState(l4sEnabled: Bool?) {
Expand All @@ -494,50 +492,72 @@ public final class QUICPath: MultiplexingDatagramPath<
func markAsBackground(_ background: Bool) {
#if !NETWORK_EMBEDDED
// Use LEDBAT for background cases
switch self.congestionControl {
switch self.congestionControl.algorithm {
case .cubic:
if !background { return } // Nothing to do, already not background
let oldState = self.congestionControl.state
var newState = CongestionControlState()
var ledbat = Ledbat(
state: &newState,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
ledbat.inherit(
from: self.congestionControl!,
from: oldState,
state: &newState,
mss: self.initialMSS,
qlog: parentProtocol.qLog
)
self.congestionControl = .ledbat(algorithm: ledbat)
self.congestionControl = CongestionControl(
state: newState,
log: self.log,
algorithm: .ledbat(algorithm: ledbat)
)
case .ledbat:
if background { return } // Nothing to do, already background
// Inherit from the current LEDBAT so bytes in flight (and the window) carry over.
let oldState = self.congestionControl.state
var newState = CongestionControlState()
var cubic = Cubic(
state: &newState,
pacer: &self.pacer,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
cubic.inherit(
from: self.congestionControl!,
from: oldState,
state: &newState,
mss: self.initialMSS,
qlog: parentProtocol.qLog
)
self.congestionControl = .cubic(algorithm: cubic)
self.congestionControl = CongestionControl(
state: newState,
log: self.log,
algorithm: .cubic(algorithm: cubic)
)
case .prague:
if !background { return } // Nothing to do, already not background
let oldState = self.congestionControl.state
var newState = CongestionControlState()
var ledbat = Ledbat(
state: &newState,
mss: self.initialMSS,
qlog: parentProtocol.qLog,
logPrefixer: self.log
)
ledbat.inherit(
from: self.congestionControl!,
from: oldState,
state: &newState,
mss: self.initialMSS,
qlog: parentProtocol.qLog
)
self.congestionControl = .ledbat(algorithm: ledbat)
case .none:
break
self.congestionControl = CongestionControl(
state: newState,
log: self.log,
algorithm: .ledbat(algorithm: ledbat)
)
}
#endif
}
Expand Down Expand Up @@ -718,22 +738,22 @@ public final class QUICPath: MultiplexingDatagramPath<
extension QUICPath {
@inline(always)
var congestionControlWindow: UInt64 {
congestionControl?.congestionWindow ?? 0
congestionControl.congestionWindow
}

@inline(always)
var congestionControlAvailableCongestionWindow: UInt64 {
congestionControl?.availableCongestionWindow ?? 0
congestionControl.availableCongestionWindow
}

@inline(always)
func congestionControlCanSend(packetLength: Int) -> Bool {
congestionControl?.canSend(packetLength: packetLength) ?? false
congestionControl.canSend(packetLength: packetLength)
}

@inline(always)
func congestionControlPersistentCongestion(mss: Int, qlog: QLog? = nil) {
congestionControl?.persistentCongestion(mss: mss, qlog: qlog)
congestionControl.persistentCongestion(mss: mss, qlog: qlog)
}

@inline(always)
Expand All @@ -744,7 +764,7 @@ extension QUICPath {
packetsLost: Bool,
qlog: QLog? = nil
) {
congestionControl?.ackEnd(
congestionControl.ackEnd(
rtt: rtt,
path: self,
mss: mss,
Expand All @@ -756,12 +776,12 @@ extension QUICPath {

@inline(always)
func congestionControlPacketsSent(bytesSent: Int, qlog: QLog? = nil) {
congestionControl?.packetSent(bytesSent: bytesSent, qlog: qlog)
congestionControl.packetSent(bytesSent: bytesSent, qlog: qlog)
}

@inline(always)
func congestionControlPacketsAcked(bytesAcked: Int, sentTime: NetworkClock.Instant) {
congestionControl?.packetsAcked(bytesAcked: bytesAcked, sentTime: sentTime)
congestionControl.packetsAcked(bytesAcked: bytesAcked, sentTime: sentTime)
}

@inline(always)
Expand All @@ -773,49 +793,49 @@ extension QUICPath {
) -> Bool {
// Loss accounting doesn't repace this path, so there is no path to hand down.
let unpacedPath: QUICPath? = nil
return congestionControl?.packetsLost(
return congestionControl.packetsLost(
path: unpacedPath,
bytesLost: bytesLost,
largestLostSentTime: largestLostSentTime,
mss: mss,
smoothedRTT: smoothedRTT,
now: parentProtocol.now
) ?? false
)
}

@inline(always)
func congestionControlPacketDiscarded(bytesSent: Int, qlog: QLog? = nil) {
congestionControl?.packetDiscarded(bytesSent: bytesSent, qlog: qlog)
congestionControl.packetDiscarded(bytesSent: bytesSent, qlog: qlog)
}

@inline(always)
func congestionControlAckBegin() {
congestionControl?.ackBegin()
congestionControl.ackBegin()
}

@inline(always)
var congestionControlBytesInFlight: UInt64 {
congestionControl?.bytesInFlight ?? 0
congestionControl.bytesInFlight
}

@inline(always)
var congestionControlName: String {
congestionControl?.name ?? "none"
congestionControl.name
}

@inline(always)
func congestionControlSpuriousRetransmit(qlog: QLog? = nil) {
congestionControl?.spuriousRetransmit(qlog: qlog)
congestionControl.spuriousRetransmit(qlog: qlog)
}

@inline(always)
func congestionControlMSSChanged(mss: Int) {
congestionControl?.mssChanged(mss: mss)
congestionControl.mssChanged(mss: mss)
}

@inline(always)
func congestionControlIdleTimeout(mss: Int) {
congestionControl?.idleTimeout(mss: mss)
congestionControl.idleTimeout(mss: mss)
}

@inline(always)
Expand All @@ -831,7 +851,7 @@ extension QUICPath {
) {
// ECN accounting doesn't repace this path, so there is no path to hand down.
let unpacedPath: QUICPath? = nil
congestionControl?.processECN(
congestionControl.processECN(
path: unpacedPath,
ceCount: ceCount,
packetsAcked: packetsAcked,
Expand All @@ -847,7 +867,7 @@ extension QUICPath {

@inline(always)
func congestionControlFilloutDataTransferSnapshot(snapshot: inout DataTransferSnapshot) {
congestionControl?.filloutDataTransferSnapshot(dataTransferSnapshot: &snapshot)
congestionControl.filloutDataTransferSnapshot(dataTransferSnapshot: &snapshot)
}
}

Expand Down
26 changes: 15 additions & 11 deletions Sources/SwiftNetwork/QUIC/Recovery.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -129,32 +129,32 @@ struct Recovery: ~Copyable, PrefixedLoggable, NonCopyableTimerUser {
if frontNumber == target { return 0 }
if frontNumber > target { return nil }

var right = entryCount - 1
var right = entryCount &- 1
let backNumber = outstandingPackets[right].packet.number.value
if backNumber == target { return right }
if backNumber < target { return nil }

// Both ends are strictly inside the range now, so narrow the window
// using the density bounds described above.
var left = 1
let fromFront = target - frontNumber
let fromFront = target &- frontNumber
if fromFront < Int64(right) {
right = Int(fromFront)
}
let fromBack = backNumber - target
if fromBack < Int64(entryCount - 1 - left) {
left = entryCount - 1 - Int(fromBack)
let fromBack = backNumber &- target
if fromBack < Int64(entryCount &- 1 &- left) {
left = entryCount &- 1 &- Int(fromBack)
}

while left <= right {
let middle = left + (right - left) / 2
let middle = left &+ (right &- left) / 2
let middleNumber = outstandingPackets[middle].packet.number.value
if middleNumber == target {
return middle
} else if middleNumber < target {
left = middle + 1
left = middle &+ 1
} else {
right = middle - 1
right = middle &- 1
}
}
return nil
Expand All @@ -172,7 +172,7 @@ struct Recovery: ~Copyable, PrefixedLoggable, NonCopyableTimerUser {
? outstandingPackets.removeFirst()
: outstandingPackets.remove(at: index)
if removedEntry.packet.largerPacket, largerPacketCount > 0 {
largerPacketCount -= 1
largerPacketCount &-= 1
}
return removedEntry
}
Expand Down Expand Up @@ -543,10 +543,14 @@ struct Recovery: ~Copyable, PrefixedLoggable, NonCopyableTimerUser {
newlyECTAcked += 1
}

guard let sentPath = connection.path(for: ackedEntry.packet.sentPath) else {
let sentPath: QUICPath
if ackedEntry.packet.sentPath == path.pathIdentifier {
sentPath = path
} else if let lookedUpPath = connection.path(for: ackedEntry.packet.sentPath) {
sentPath = lookedUpPath
} else {
continue
}

if ackedEntry.lostTime != .zero {
let sRTT = sentPath.rtt.smoothedRTT
let latestRTT = sentPath.rtt.latestRTT
Expand Down
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