Expose TCP RTT

PiperOrigin-RevId: 211504634
Change-Id: I9a7bcbbdd40e5036894930f709278725ef477293

pkg/tcpip/tcpip.go

@@ -430,7 +430,10 @@ type TimestampOption int
 // TCPInfoOption is used by GetSockOpt to expose TCP statistics.
 //
 // TODO: Add and populate stat fields.
-type TCPInfoOption struct{}
+type TCPInfoOption struct {
+	RTT    time.Duration
+	RTTVar time.Duration
+}
 
 // Route is a row in the routing table. It specifies through which NIC (and
 // gateway) sets of packets should be routed. A row is considered viable if the

pkg/tcpip/transport/tcp/cubic.go

@@ -129,7 +129,10 @@ func (c *cubicState) Update(packetsAcked int) {
 			return
 		}
 	} else {
-		c.s.sndCwnd = c.getCwnd(packetsAcked, c.s.sndCwnd, c.s.srtt)
+		c.s.rtt.Lock()
+		srtt := c.s.rtt.srtt
+		c.s.rtt.Unlock()
+		c.s.sndCwnd = c.getCwnd(packetsAcked, c.s.sndCwnd, srtt)
 	}
 }
 

pkg/tcpip/transport/tcp/endpoint.go

@@ -788,6 +788,16 @@ func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 
 	case *tcpip.TCPInfoOption:
 		*o = tcpip.TCPInfoOption{}
+		e.mu.RLock()
+		snd := e.snd
+		e.mu.RUnlock()
+		if snd != nil {
+			snd.rtt.Lock()
+			o.RTT = snd.rtt.srtt
+			o.RTTVar = snd.rtt.rttvar
+			snd.rtt.Unlock()
+		}
+
 		return nil
 	}
 
@@ -1463,13 +1473,15 @@ func (e *endpoint) completeState() stack.TCPEndpointState {
 		RTTMeasureSeqNum: e.snd.rttMeasureSeqNum,
 		RTTMeasureTime:   e.snd.rttMeasureTime,
 		Closed:           e.snd.closed,
-		SRTT:             e.snd.srtt,
 		RTO:              e.snd.rto,
 		SRTTInited:       e.snd.srttInited,
 		MaxPayloadSize:   e.snd.maxPayloadSize,
 		SndWndScale:      e.snd.sndWndScale,
 		MaxSentAck:       e.snd.maxSentAck,
 	}
+	e.snd.rtt.Lock()
+	s.Sender.SRTT = e.snd.rtt.srtt
+	e.snd.rtt.Unlock()
 
 	if cubic, ok := e.snd.cc.(*cubicState); ok {
 		s.Sender.Cubic = stack.TCPCubicState{

pkg/tcpip/transport/tcp/snd.go

@@ -16,6 +16,7 @@ package tcp
 
 import (
 	"math"
+	"sync"
 	"time"
 
 	"gvisor.googlesource.com/gvisor/pkg/sleep"
@@ -116,11 +117,10 @@ type sender struct {
 	resendTimer timer       `state:"nosave"`
 	resendWaker sleep.Waker `state:"nosave"`
 
-	// srtt, rttvar & rto are the "smoothed round-trip time", "round-trip
-	// time variation" and "retransmit timeout", as defined in section 2 of
-	// RFC 6298.
-	srtt       time.Duration
-	rttvar     time.Duration
+	// rtt.srtt, rtt.rttvar, and rto are the "smoothed round-trip time",
+	// "round-trip time variation" and "retransmit timeout", as defined in
+	// section 2 of RFC 6298.
+	rtt        rtt
 	rto        time.Duration
 	srttInited bool
 
@@ -139,6 +139,17 @@ type sender struct {
 	cc congestionControl
 }
 
+// rtt is a synchronization wrapper used to appease stateify. See the comment
+// in sender, where it is used.
+//
+// +stateify savable
+type rtt struct {
+	sync.Mutex `state:"nosave"`
+
+	srtt   time.Duration
+	rttvar time.Duration
+}
+
 // fastRecovery holds information related to fast recovery from a packet loss.
 //
 // +stateify savable
@@ -265,20 +276,22 @@ func (s *sender) sendAck() {
 // updateRTO updates the retransmit timeout when a new roud-trip time is
 // available. This is done in accordance with section 2 of RFC 6298.
 func (s *sender) updateRTO(rtt time.Duration) {
+	s.rtt.Lock()
 	if !s.srttInited {
-		s.rttvar = rtt / 2
-		s.srtt = rtt
+		s.rtt.rttvar = rtt / 2
+		s.rtt.srtt = rtt
 		s.srttInited = true
 	} else {
-		diff := s.srtt - rtt
+		diff := s.rtt.srtt - rtt
 		if diff < 0 {
 			diff = -diff
 		}
-		s.rttvar = (3*s.rttvar + diff) / 4
-		s.srtt = (7*s.srtt + rtt) / 8
+		s.rtt.rttvar = (3*s.rtt.rttvar + diff) / 4
+		s.rtt.srtt = (7*s.rtt.srtt + rtt) / 8
 	}
 
-	s.rto = s.srtt + 4*s.rttvar
+	s.rto = s.rtt.srtt + 4*s.rtt.rttvar
+	s.rtt.Unlock()
 	if s.rto < minRTO {
 		s.rto = minRTO
 	}