quic: add qlog recovery metrics

Log events for various congestion control and loss recovery metrics.

For golang/go#58547

Change-Id: Ife3b3897f6ca731049c78b934a7123aa1ed4aee2
Reviewed-on: https://go-review.googlesource.com/c/net/+/564016
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

internal/quic/congestion_reno.go

@@ -7,6 +7,8 @@
 package quic
 
 import (
+	"context"
+	"log/slog"
 	"math"
 	"time"
 )
@@ -40,6 +42,9 @@ type ccReno struct {
 	// true if we haven't sent that packet yet.
 	sendOnePacketInRecovery bool
 
+	// inRecovery is set when we are in the recovery state.
+	inRecovery bool
+
 	// underutilized is set if the congestion window is underutilized
 	// due to insufficient application data, flow control limits, or
 	// anti-amplification limits.
@@ -100,12 +105,19 @@ func (c *ccReno) canSend() bool {
 // congestion controller permits sending data, but no data is sent.
 //
 // https://www.rfc-editor.org/rfc/rfc9002#section-7.8
-func (c *ccReno) setUnderutilized(v bool) {
+func (c *ccReno) setUnderutilized(log *slog.Logger, v bool) {
+	if c.underutilized == v {
+		return
+	}
+	oldState := c.state()
 	c.underutilized = v
+	if logEnabled(log, QLogLevelPacket) {
+		logCongestionStateUpdated(log, oldState, c.state())
+	}
 }
 
 // packetSent indicates that a packet has been sent.
-func (c *ccReno) packetSent(now time.Time, space numberSpace, sent *sentPacket) {
+func (c *ccReno) packetSent(now time.Time, log *slog.Logger, space numberSpace, sent *sentPacket) {
 	if !sent.inFlight {
 		return
 	}
@@ -185,7 +197,11 @@ func (c *ccReno) packetLost(now time.Time, space numberSpace, sent *sentPacket,
 }
 
 // packetBatchEnd is called at the end of processing a batch of acked or lost packets.
-func (c *ccReno) packetBatchEnd(now time.Time, space numberSpace, rtt *rttState, maxAckDelay time.Duration) {
+func (c *ccReno) packetBatchEnd(now time.Time, log *slog.Logger, space numberSpace, rtt *rttState, maxAckDelay time.Duration) {
+	if logEnabled(log, QLogLevelPacket) {
+		oldState := c.state()
+		defer func() { logCongestionStateUpdated(log, oldState, c.state()) }()
+	}
 	if !c.ackLastLoss.IsZero() && !c.ackLastLoss.Before(c.recoveryStartTime) {
 		// Enter the recovery state.
 		// https://www.rfc-editor.org/rfc/rfc9002.html#section-7.3.2
@@ -196,8 +212,10 @@ func (c *ccReno) packetBatchEnd(now time.Time, space numberSpace, rtt *rttState,
 		// Clear congestionPendingAcks to avoid increasing the congestion
 		// window based on acks in a frame that sends us into recovery.
 		c.congestionPendingAcks = 0
+		c.inRecovery = true
 	} else if c.congestionPendingAcks > 0 {
 		// We are in slow start or congestion avoidance.
+		c.inRecovery = false
 		if c.congestionWindow < c.slowStartThreshold {
 			// When the congestion window is less than the slow start threshold,
 			// we are in slow start and increase the window by the number of
@@ -253,3 +271,38 @@ func (c *ccReno) minimumCongestionWindow() int {
 	// https://www.rfc-editor.org/rfc/rfc9002.html#section-7.2-4
 	return 2 * c.maxDatagramSize
 }
+
+func logCongestionStateUpdated(log *slog.Logger, oldState, newState congestionState) {
+	if oldState == newState {
+		return
+	}
+	log.LogAttrs(context.Background(), QLogLevelPacket,
+		"recovery:congestion_state_updated",
+		slog.String("old", oldState.String()),
+		slog.String("new", newState.String()),
+	)
+}
+
+type congestionState string
+
+func (s congestionState) String() string { return string(s) }
+
+const (
+	congestionSlowStart           = congestionState("slow_start")
+	congestionCongestionAvoidance = congestionState("congestion_avoidance")
+	congestionApplicationLimited  = congestionState("application_limited")
+	congestionRecovery            = congestionState("recovery")
+)
+
+func (c *ccReno) state() congestionState {
+	switch {
+	case c.inRecovery:
+		return congestionRecovery
+	case c.underutilized:
+		return congestionApplicationLimited
+	case c.congestionWindow < c.slowStartThreshold:
+		return congestionSlowStart
+	default:
+		return congestionCongestionAvoidance
+	}
+}

internal/quic/congestion_reno_test.go

@@ -470,7 +470,7 @@ func (c *ccTest) setRTT(smoothedRTT, rttvar time.Duration) {
 func (c *ccTest) setUnderutilized(v bool) {
 	c.t.Helper()
 	c.t.Logf("set underutilized = %v", v)
-	c.cc.setUnderutilized(v)
+	c.cc.setUnderutilized(nil, v)
 }
 
 func (c *ccTest) packetSent(space numberSpace, size int, fns ...func(*sentPacket)) *sentPacket {
@@ -488,7 +488,7 @@ func (c *ccTest) packetSent(space numberSpace, size int, fns ...func(*sentPacket
 		f(sent)
 	}
 	c.t.Logf("packet sent:  num=%v.%v, size=%v", space, sent.num, sent.size)
-	c.cc.packetSent(c.now, space, sent)
+	c.cc.packetSent(c.now, nil, space, sent)
 	return sent
 }
 
@@ -519,7 +519,7 @@ func (c *ccTest) packetDiscarded(space numberSpace, sent *sentPacket) {
 func (c *ccTest) packetBatchEnd(space numberSpace) {
 	c.t.Helper()
 	c.t.Logf("(end of batch)")
-	c.cc.packetBatchEnd(c.now, space, &c.rtt, c.maxAckDelay)
+	c.cc.packetBatchEnd(c.now, nil, space, &c.rtt, c.maxAckDelay)
 }
 
 func (c *ccTest) wantCanSend(want bool) {

internal/quic/conn.go

@@ -210,7 +210,7 @@ func (c *Conn) discardKeys(now time.Time, space numberSpace) {
 	case handshakeSpace:
 		c.keysHandshake.discard()
 	}
-	c.loss.discardKeys(now, space)
+	c.loss.discardKeys(now, c.log, space)
 }
 
 // receiveTransportParameters applies transport parameters sent by the peer.

internal/quic/conn_loss.go

@@ -20,6 +20,10 @@ import "fmt"
 // See RFC 9000, Section 13.3 for a complete list of information which is retransmitted on loss.
 // https://www.rfc-editor.org/rfc/rfc9000#section-13.3
 func (c *Conn) handleAckOrLoss(space numberSpace, sent *sentPacket, fate packetFate) {
+	if fate == packetLost && c.logEnabled(QLogLevelPacket) {
+		c.logPacketLost(space, sent)
+	}
+
 	// The list of frames in a sent packet is marshaled into a buffer in the sentPacket
 	// by the packetWriter. Unmarshal that buffer here. This code must be kept in sync with
 	// packetWriter.append*.

internal/quic/conn_recv.go

@@ -192,7 +192,7 @@ func (c *Conn) handleRetry(now time.Time, pkt []byte) {
 	c.connIDState.handleRetryPacket(p.srcConnID)
 	// We need to resend any data we've already sent in Initial packets.
 	// We must not reuse already sent packet numbers.
-	c.loss.discardPackets(initialSpace, c.handleAckOrLoss)
+	c.loss.discardPackets(initialSpace, c.log, c.handleAckOrLoss)
 	// TODO: Discard 0-RTT packets as well, once we support 0-RTT.
 }
 
@@ -416,7 +416,7 @@ func (c *Conn) handleAckFrame(now time.Time, space numberSpace, payload []byte)
 	if c.peerAckDelayExponent >= 0 {
 		delay = ackDelay.Duration(uint8(c.peerAckDelayExponent))
 	}
-	c.loss.receiveAckEnd(now, space, delay, c.handleAckOrLoss)
+	c.loss.receiveAckEnd(now, c.log, space, delay, c.handleAckOrLoss)
 	if space == appDataSpace {
 		c.keysAppData.handleAckFor(largest)
 	}

internal/quic/conn_send.go

@@ -22,7 +22,10 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 	// Assumption: The congestion window is not underutilized.
 	// If congestion control, pacing, and anti-amplification all permit sending,
 	// but we have no packet to send, then we will declare the window underutilized.
-	c.loss.cc.setUnderutilized(false)
+	underutilized := false
+	defer func() {
+		c.loss.cc.setUnderutilized(c.log, underutilized)
+	}()
 
 	// Send one datagram on each iteration of this loop,
 	// until we hit a limit or run out of data to send.
@@ -80,7 +83,6 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 			}
 			sentInitial = c.w.finishProtectedLongHeaderPacket(pnumMaxAcked, c.keysInitial.w, p)
 			if sentInitial != nil {
-				c.idleHandlePacketSent(now, sentInitial)
 				// Client initial packets and ack-eliciting server initial packaets
 				// need to be sent in a datagram padded to at least 1200 bytes.
 				// We can't add the padding yet, however, since we may want to
@@ -111,8 +113,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 				c.logPacketSent(packetTypeHandshake, pnum, p.srcConnID, p.dstConnID, c.w.packetLen(), c.w.payload())
 			}
 			if sent := c.w.finishProtectedLongHeaderPacket(pnumMaxAcked, c.keysHandshake.w, p); sent != nil {
-				c.idleHandlePacketSent(now, sent)
-				c.loss.packetSent(now, handshakeSpace, sent)
+				c.packetSent(now, handshakeSpace, sent)
 				if c.side == clientSide {
 					// "[...] a client MUST discard Initial keys when it first
 					// sends a Handshake packet [...]"
@@ -142,8 +143,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 				c.logPacketSent(packetType1RTT, pnum, nil, dstConnID, c.w.packetLen(), c.w.payload())
 			}
 			if sent := c.w.finish1RTTPacket(pnum, pnumMaxAcked, dstConnID, &c.keysAppData); sent != nil {
-				c.idleHandlePacketSent(now, sent)
-				c.loss.packetSent(now, appDataSpace, sent)
+				c.packetSent(now, appDataSpace, sent)
 			}
 		}
 
@@ -152,7 +152,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 			if limit == ccOK {
 				// We have nothing to send, and congestion control does not
 				// block sending. The congestion window is underutilized.
-				c.loss.cc.setUnderutilized(true)
+				underutilized = true
 			}
 			return next
 		}
@@ -175,14 +175,19 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 			// with a Handshake packet, then we've discarded Initial keys
 			// since constructing the packet and shouldn't record it as in-flight.
 			if c.keysInitial.canWrite() {
-				c.loss.packetSent(now, initialSpace, sentInitial)
+				c.packetSent(now, initialSpace, sentInitial)
 			}
 		}
 
 		c.endpoint.sendDatagram(buf, c.peerAddr)
 	}
 }
 
+func (c *Conn) packetSent(now time.Time, space numberSpace, sent *sentPacket) {
+	c.idleHandlePacketSent(now, sent)
+	c.loss.packetSent(now, c.log, space, sent)
+}
+
 func (c *Conn) appendFrames(now time.Time, space numberSpace, pnum packetNumber, limit ccLimit) {
 	if c.lifetime.localErr != nil {
 		c.appendConnectionCloseFrame(now, space, c.lifetime.localErr)

internal/quic/loss.go

@@ -7,6 +7,8 @@
 package quic
 
 import (
+	"context"
+	"log/slog"
 	"math"
 	"time"
 )
@@ -179,21 +181,24 @@ func (c *lossState) nextNumber(space numberSpace) packetNumber {
 }
 
 // packetSent records a sent packet.
-func (c *lossState) packetSent(now time.Time, space numberSpace, sent *sentPacket) {
+func (c *lossState) packetSent(now time.Time, log *slog.Logger, space numberSpace, sent *sentPacket) {
 	sent.time = now
 	c.spaces[space].add(sent)
 	size := sent.size
 	if c.antiAmplificationLimit != antiAmplificationUnlimited {
 		c.antiAmplificationLimit = max(0, c.antiAmplificationLimit-size)
 	}
 	if sent.inFlight {
-		c.cc.packetSent(now, space, sent)
+		c.cc.packetSent(now, log, space, sent)
 		c.pacer.packetSent(now, size, c.cc.congestionWindow, c.rtt.smoothedRTT)
 		if sent.ackEliciting {
 			c.spaces[space].lastAckEliciting = sent.num
 			c.ptoExpired = false // reset expired PTO timer after sending probe
 		}
 		c.scheduleTimer(now)
+		if logEnabled(log, QLogLevelPacket) {
+			logBytesInFlight(log, c.cc.bytesInFlight)
+		}
 	}
 	if sent.ackEliciting {
 		c.consecutiveNonAckElicitingPackets = 0
@@ -267,7 +272,7 @@ func (c *lossState) receiveAckRange(now time.Time, space numberSpace, rangeIndex
 
 // receiveAckEnd finishes processing an ack frame.
 // The lossf function is called for each packet newly detected as lost.
-func (c *lossState) receiveAckEnd(now time.Time, space numberSpace, ackDelay time.Duration, lossf func(numberSpace, *sentPacket, packetFate)) {
+func (c *lossState) receiveAckEnd(now time.Time, log *slog.Logger, space numberSpace, ackDelay time.Duration, lossf func(numberSpace, *sentPacket, packetFate)) {
 	c.spaces[space].sentPacketList.clean()
 	// Update the RTT sample when the largest acknowledged packet in the ACK frame
 	// is newly acknowledged, and at least one newly acknowledged packet is ack-eliciting.
@@ -286,24 +291,44 @@ func (c *lossState) receiveAckEnd(now time.Time, space numberSpace, ackDelay tim
 	// https://www.rfc-editor.org/rfc/rfc9002.html#section-6.2.2.1-3
 	c.timer = time.Time{}
 	c.detectLoss(now, lossf)
-	c.cc.packetBatchEnd(now, space, &c.rtt, c.maxAckDelay)
+	c.cc.packetBatchEnd(now, log, space, &c.rtt, c.maxAckDelay)
+
+	if logEnabled(log, QLogLevelPacket) {
+		var ssthresh slog.Attr
+		if c.cc.slowStartThreshold != math.MaxInt {
+			ssthresh = slog.Int("ssthresh", c.cc.slowStartThreshold)
+		}
+		log.LogAttrs(context.Background(), QLogLevelPacket,
+			"recovery:metrics_updated",
+			slog.Duration("min_rtt", c.rtt.minRTT),
+			slog.Duration("smoothed_rtt", c.rtt.smoothedRTT),
+			slog.Duration("latest_rtt", c.rtt.latestRTT),
+			slog.Duration("rtt_variance", c.rtt.rttvar),
+			slog.Int("congestion_window", c.cc.congestionWindow),
+			slog.Int("bytes_in_flight", c.cc.bytesInFlight),
+			ssthresh,
+		)
+	}
 }
 
 // discardPackets declares that packets within a number space will not be delivered
 // and that data contained in them should be resent.
 // For example, after receiving a Retry packet we discard already-sent Initial packets.
-func (c *lossState) discardPackets(space numberSpace, lossf func(numberSpace, *sentPacket, packetFate)) {
+func (c *lossState) discardPackets(space numberSpace, log *slog.Logger, lossf func(numberSpace, *sentPacket, packetFate)) {
 	for i := 0; i < c.spaces[space].size; i++ {
 		sent := c.spaces[space].nth(i)
 		sent.lost = true
 		c.cc.packetDiscarded(sent)
 		lossf(numberSpace(space), sent, packetLost)
 	}
 	c.spaces[space].clean()
+	if logEnabled(log, QLogLevelPacket) {
+		logBytesInFlight(log, c.cc.bytesInFlight)
+	}
 }
 
 // discardKeys is called when dropping packet protection keys for a number space.
-func (c *lossState) discardKeys(now time.Time, space numberSpace) {
+func (c *lossState) discardKeys(now time.Time, log *slog.Logger, space numberSpace) {
 	// https://www.rfc-editor.org/rfc/rfc9002.html#section-6.4
 	for i := 0; i < c.spaces[space].size; i++ {
 		sent := c.spaces[space].nth(i)
@@ -313,6 +338,9 @@ func (c *lossState) discardKeys(now time.Time, space numberSpace) {
 	c.spaces[space].maxAcked = -1
 	c.spaces[space].lastAckEliciting = -1
 	c.scheduleTimer(now)
+	if logEnabled(log, QLogLevelPacket) {
+		logBytesInFlight(log, c.cc.bytesInFlight)
+	}
 }
 
 func (c *lossState) lossDuration() time.Duration {
@@ -459,3 +487,10 @@ func (c *lossState) ptoBasePeriod() time.Duration {
 	}
 	return pto
 }
+
+func logBytesInFlight(log *slog.Logger, bytesInFlight int) {
+	log.LogAttrs(context.Background(), QLogLevelPacket,
+		"recovery:metrics_updated",
+		slog.Int("bytes_in_flight", bytesInFlight),
+	)
+}

internal/quic/loss_test.go

@@ -1060,7 +1060,7 @@ func TestLossPersistentCongestion(t *testing.T) {
 		maxDatagramSize: 1200,
 	})
 	test.send(initialSpace, 0, testSentPacketSize(1200))
-	test.c.cc.setUnderutilized(true)
+	test.c.cc.setUnderutilized(nil, true)
 
 	test.advance(10 * time.Millisecond)
 	test.ack(initialSpace, 0*time.Millisecond, i64range[packetNumber]{0, 1})
@@ -1377,7 +1377,7 @@ func (c *lossTest) setRTTVar(d time.Duration) {
 
 func (c *lossTest) setUnderutilized(v bool) {
 	c.t.Logf("set congestion window underutilized: %v", v)
-	c.c.cc.setUnderutilized(v)
+	c.c.cc.setUnderutilized(nil, v)
 }
 
 func (c *lossTest) advance(d time.Duration) {
@@ -1438,7 +1438,7 @@ func (c *lossTest) send(spaceID numberSpace, opts ...any) {
 		sent := &sentPacket{}
 		*sent = prototype
 		sent.num = num
-		c.c.packetSent(c.now, spaceID, sent)
+		c.c.packetSent(c.now, nil, spaceID, sent)
 	}
 }
 
@@ -1462,7 +1462,7 @@ func (c *lossTest) ack(spaceID numberSpace, ackDelay time.Duration, rs ...i64ran
 		c.t.Logf("ack %v delay=%v [%v,%v)", spaceID, ackDelay, r.start, r.end)
 		c.c.receiveAckRange(c.now, spaceID, i, r.start, r.end, c.onAckOrLoss)
 	}
-	c.c.receiveAckEnd(c.now, spaceID, ackDelay, c.onAckOrLoss)
+	c.c.receiveAckEnd(c.now, nil, spaceID, ackDelay, c.onAckOrLoss)
 }
 
 func (c *lossTest) onAckOrLoss(space numberSpace, sent *sentPacket, fate packetFate) {
@@ -1491,7 +1491,7 @@ func (c *lossTest) discardKeys(spaceID numberSpace) {
 	c.t.Helper()
 	c.checkUnexpectedEvents()
 	c.t.Logf("discard %s keys", spaceID)
-	c.c.discardKeys(c.now, spaceID)
+	c.c.discardKeys(c.now, nil, spaceID)
 }
 
 func (c *lossTest) setMaxAckDelay(d time.Duration) {