wip: BBR experimental changes

core/internal/congestion/bbr/bbr_sender.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"math/rand"
 	"net"
+	"os"
+	"strconv"
 	"time"
 
 	"github.com/apernet/quic-go/congestion"
@@ -37,6 +39,8 @@ const (
 	derivedHighGain = 2.773
 	// The newly derived CWND gain for STARTUP, 2.
 	derivedHighCWNDGain = 2.0
+
+	debugEnv = "HYSTERIA_BBR_DEBUG"
 )
 
 // The cycle of gains used during the PROBE_BW stage.
@@ -61,7 +65,7 @@ const (
 	// Flag.
 	defaultStartupFullLossCount  = 8
 	quicBbr2DefaultLossThreshold = 0.02
-	maxBbrBurstPackets           = 3
+	maxBbrBurstPackets           = 10
 )
 
 type bbrMode int
@@ -237,6 +241,8 @@ type bbrSender struct {
 	maxDatagramSize congestion.ByteCount
 	// Recorded on packet sent. equivalent |unacked_packets_->bytes_in_flight()|
 	bytesInFlight congestion.ByteCount
+
+	debug bool
 }
 
 var _ congestion.CongestionControl = &bbrSender{}
@@ -259,6 +265,7 @@ func newBbrSender(
 	initialCongestionWindow,
 	initialMaxCongestionWindow congestion.ByteCount,
 ) *bbrSender {
+	debug, _ := strconv.ParseBool(os.Getenv(debugEnv))
 	b := &bbrSender{
 		clock:                        clock,
 		mode:                         bbrModeStartup,
@@ -284,6 +291,7 @@ func newBbrSender(
 		cwndToCalculateMinPacingRate:                     initialCongestionWindow,
 		maxCongestionWindowWithNetworkParametersAdjusted: initialMaxCongestionWindow,
 		maxDatagramSize: initialMaxDatagramSize,
+		debug:           debug,
 	}
 	b.pacer = common.NewPacer(b.bandwidthForPacer)
 
@@ -332,6 +340,8 @@ func (b *bbrSender) OnPacketSent(
 	}
 
 	b.sampler.OnPacketSent(sentTime, packetNumber, bytes, bytesInFlight, isRetransmittable)
+
+	b.maybeAppLimited(bytesInFlight)
 }
 
 // CanSend implements the SendAlgorithm interface.
@@ -411,8 +421,6 @@ func (b *bbrSender) OnCongestionEventEx(priorInFlight congestion.ByteCount, even
 	// packet in lost_packets.
 	var lastPacketSendState sendTimeState
 
-	b.maybeApplimited(priorInFlight)
-
 	// Update bytesInFlight
 	b.bytesInFlight = priorInFlight
 	for _, p := range ackedPackets {
@@ -539,7 +547,7 @@ func (b *bbrSender) setDrainGain(drainGain float64) {
 	b.drainGain = drainGain
 }
 
-// What's the current estimated bandwidth in bytes per second.
+// Get the current bandwidth estimate. Note that Bandwidth is in bits per second.
 func (b *bbrSender) bandwidthEstimate() Bandwidth {
 	return b.maxBandwidth.GetBest()
 }
@@ -607,6 +615,10 @@ func (b *bbrSender) enterStartupMode(now time.Time) {
 	// b.maybeTraceStateChange(logging.CongestionStateStartup)
 	b.pacingGain = b.highGain
 	b.congestionWindowGain = b.highCwndGain
+
+	if b.debug {
+		b.debugPrint("Phase: STARTUP")
+	}
 }
 
 // Enters the PROBE_BW mode.
@@ -625,6 +637,10 @@ func (b *bbrSender) enterProbeBandwidthMode(now time.Time) {
 
 	b.lastCycleStart = now
 	b.pacingGain = pacingGain[b.cycleCurrentOffset]
+
+	if b.debug {
+		b.debugPrint("Phase: PROBE_BW")
+	}
 }
 
 // Updates the round-trip counter if a round-trip has passed.  Returns true if
@@ -698,15 +714,17 @@ func (b *bbrSender) checkIfFullBandwidthReached(lastPacketSendState *sendTimeSta
 	}
 }
 
-func (b *bbrSender) maybeApplimited(bytesInFlight congestion.ByteCount) {
+func (b *bbrSender) maybeAppLimited(bytesInFlight congestion.ByteCount) {
 	congestionWindow := b.GetCongestionWindow()
 	if bytesInFlight >= congestionWindow {
 		return
 	}
 	availableBytes := congestionWindow - bytesInFlight
-	drainLimited := b.mode == bbrModeDrain && bytesInFlight > congestionWindow/2
-	if !drainLimited || availableBytes > maxBbrBurstPackets*b.maxDatagramSize {
+	if availableBytes > maxBbrBurstPackets*b.maxDatagramSize {
 		b.sampler.OnAppLimited()
+		if b.debug {
+			b.debugPrint("AppLimited, AvailableBytes: %d", availableBytes)
+		}
 	}
 }
 
@@ -718,6 +736,10 @@ func (b *bbrSender) maybeExitStartupOrDrain(now time.Time) {
 		// b.maybeTraceStateChange(logging.CongestionStateDrain)
 		b.pacingGain = b.drainGain
 		b.congestionWindowGain = b.highCwndGain
+
+		if b.debug {
+			b.debugPrint("Phase: DRAIN")
+		}
 	}
 	if b.mode == bbrModeDrain && b.bytesInFlight <= b.getTargetCongestionWindow(1) {
 		b.enterProbeBandwidthMode(now)
@@ -733,6 +755,12 @@ func (b *bbrSender) maybeEnterOrExitProbeRtt(now time.Time, isRoundStart, minRtt
 		// 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.debug {
+			b.debugPrint("BandwidthEstimate: %s, CongestionWindowGain: %.2f, PacingGain: %.2f, PacingRate: %s",
+				formatSpeed(b.bandwidthEstimate()), b.congestionWindowGain, b.pacingGain, formatSpeed(b.PacingRate()))
+			b.debugPrint("Phase: PROBE_RTT")
+		}
 	}
 
 	if b.mode == bbrModeProbeRtt {
@@ -925,6 +953,12 @@ func (b *bbrSender) shouldExitStartupDueToLoss(lastPacketSendState *sendTimeStat
 	return false
 }
 
+func (b *bbrSender) debugPrint(format string, a ...any) {
+	fmt.Printf("[BBRSender] [%s] %s\n",
+		time.Now().Format("15:04:05"),
+		fmt.Sprintf(format, a...))
+}
+
 func bdpFromRttAndBandwidth(rtt time.Duration, bandwidth Bandwidth) congestion.ByteCount {
 	return congestion.ByteCount(rtt) * congestion.ByteCount(bandwidth) / congestion.ByteCount(BytesPerSecond) / congestion.ByteCount(time.Second)
 }
@@ -942,3 +976,14 @@ func GetInitialPacketSize(addr net.Addr) congestion.ByteCount {
 		return congestion.MinInitialPacketSize
 	}
 }
+
+func formatSpeed(bw Bandwidth) string {
+	bwf := float64(bw)
+	units := []string{"bps", "Kbps", "Mbps", "Gbps"}
+	unitIndex := 0
+	for bwf > 1024 && unitIndex < len(units)-1 {
+		bwf /= 1024
+		unitIndex++
+	}
+	return fmt.Sprintf("%.2f %s", bwf, units[unitIndex])
+}