Avoid unnecessary work in transportDemuxer.deliverPacket().

- Don't allocate []*endpointsByNic in transportDemuxer.deliverPacket() unless
  actually needed for UDP broadcast/multicast.

- Don't allocate []*endpointsByNic via transportDemuxer.findEndpointLocked()
  => transportDemuxer.findAllEndpointsLocked().

- Skip unnecessary map lookups in transportDemuxer.findEndpointLocked() =>
  transportDemuxer.findAllEndpointsLocked() (now iterEndpointsLocked).

For most deliverable packets other than UDP broadcast/multicast packets, this
saves two slice allocations and three map lookups per packet.

PiperOrigin-RevId: 300804135

1 files changed, 59 insertions, 53 deletions

diff --git a/pkg/tcpip/stack/transport_demuxer.go b/pkg/tcpip/stack/transport_demuxer.go
index ff1845bfb..d4c0359e8 100644
--- a/pkg/tcpip/stack/transport_demuxer.go
+++ b/pkg/tcpip/stack/transport_demuxer.go
@@ -409,61 +409,45 @@ func (d *transportDemuxer) deliverPacket(r *Route, protocol tcpip.TransportProto
 		return false
 	}
 
-	eps.mu.RLock()
-
-	// Determine which transport endpoint or endpoints to deliver this packet to.
 	// If the packet is a UDP broadcast or multicast, then find all matching
-	// transport endpoints. If the packet is a TCP packet with a non-unicast
-	// source or destination address, then do nothing further and instruct
-	// the caller to do the same.
-	var destEps []*endpointsByNic
-	switch protocol {
-	case header.UDPProtocolNumber:
-		if isMulticastOrBroadcast(id.LocalAddress) {
-			destEps = d.findAllEndpointsLocked(eps, id)
-			break
-		}
-
-		if ep := d.findEndpointLocked(eps, id); ep != nil {
-			destEps = append(destEps, ep)
+	// transport endpoints.
+	if protocol == header.UDPProtocolNumber && isMulticastOrBroadcast(id.LocalAddress) {
+		eps.mu.RLock()
+		destEPs := d.findAllEndpointsLocked(eps, id)
+		eps.mu.RUnlock()
+		// Fail if we didn't find at least one matching transport endpoint.
+		if len(destEPs) == 0 {
+			r.Stats().UDP.UnknownPortErrors.Increment()
+			return false
 		}
-
-	case header.TCPProtocolNumber:
-		if !(isUnicast(r.LocalAddress) && isUnicast(r.RemoteAddress)) {
-			// TCP can only be used to communicate between a single
-			// source and a single destination; the addresses must
-			// be unicast.
-			eps.mu.RUnlock()
-			r.Stats().TCP.InvalidSegmentsReceived.Increment()
-			return true
+		// handlePacket takes ownership of pkt, so each endpoint needs its own
+		// copy except for the final one.
+		for _, ep := range destEPs[:len(destEPs)-1] {
+			ep.handlePacket(r, id, pkt.Clone())
 		}
+		destEPs[len(destEPs)-1].handlePacket(r, id, pkt)
+		return true
+	}
 
-		fallthrough
-
-	default:
-		if ep := d.findEndpointLocked(eps, id); ep != nil {
-			destEps = append(destEps, ep)
-		}
+	// If the packet is a TCP packet with a non-unicast source or destination
+	// address, then do nothing further and instruct the caller to do the same.
+	if protocol == header.TCPProtocolNumber && (!isUnicast(r.LocalAddress) || !isUnicast(r.RemoteAddress)) {
+		// TCP can only be used to communicate between a single source and a
+		// single destination; the addresses must be unicast.
+		r.Stats().TCP.InvalidSegmentsReceived.Increment()
+		return true
 	}
 
+	eps.mu.RLock()
+	ep := d.findEndpointLocked(eps, id)
 	eps.mu.RUnlock()
-
-	// Fail if we didn't find at least one matching transport endpoint.
-	if len(destEps) == 0 {
-		// UDP packet could not be delivered to an unknown destination port.
+	if ep == nil {
 		if protocol == header.UDPProtocolNumber {
 			r.Stats().UDP.UnknownPortErrors.Increment()
 		}
 		return false
 	}
-
-	// HandlePacket takes ownership of pkt, so each endpoint needs its own
-	// copy except for the final one.
-	for _, ep := range destEps[:len(destEps)-1] {
-		ep.handlePacket(r, id, pkt.Clone())
-	}
-	destEps[len(destEps)-1].handlePacket(r, id, pkt)
-
+	ep.handlePacket(r, id, pkt)
 	return true
 }
 
@@ -515,11 +499,17 @@ func (d *transportDemuxer) deliverControlPacket(n *NIC, net tcpip.NetworkProtoco
 	return true
 }
 
-func (d *transportDemuxer) findAllEndpointsLocked(eps *transportEndpoints, id TransportEndpointID) []*endpointsByNic {
-	var matchedEPs []*endpointsByNic
+// iterEndpointsLocked yields all endpointsByNic in eps that match id, in
+// descending order of match quality. If a call to yield returns false,
+// iterEndpointsLocked stops iteration and returns immediately.
+//
+// Preconditions: eps.mu must be locked.
+func (d *transportDemuxer) iterEndpointsLocked(eps *transportEndpoints, id TransportEndpointID, yield func(*endpointsByNic) bool) {
 	// Try to find a match with the id as provided.
 	if ep, ok := eps.endpoints[id]; ok {
-		matchedEPs = append(matchedEPs, ep)
+		if !yield(ep) {
+			return
+		}
 	}
 
 	// Try to find a match with the id minus the local address.
@@ -527,7 +517,9 @@ func (d *transportDemuxer) findAllEndpointsLocked(eps *transportEndpoints, id Tr
 
 	nid.LocalAddress = ""
 	if ep, ok := eps.endpoints[nid]; ok {
-		matchedEPs = append(matchedEPs, ep)
+		if !yield(ep) {
+			return
+		}
 	}
 
 	// Try to find a match with the id minus the remote part.
@@ -535,14 +527,26 @@ func (d *transportDemuxer) findAllEndpointsLocked(eps *transportEndpoints, id Tr
 	nid.RemoteAddress = ""
 	nid.RemotePort = 0
 	if ep, ok := eps.endpoints[nid]; ok {
-		matchedEPs = append(matchedEPs, ep)
+		if !yield(ep) {
+			return
+		}
 	}
 
 	// Try to find a match with only the local port.
 	nid.LocalAddress = ""
 	if ep, ok := eps.endpoints[nid]; ok {
-		matchedEPs = append(matchedEPs, ep)
+		if !yield(ep) {
+			return
+		}
 	}
+}
+
+func (d *transportDemuxer) findAllEndpointsLocked(eps *transportEndpoints, id TransportEndpointID) []*endpointsByNic {
+	var matchedEPs []*endpointsByNic
+	d.iterEndpointsLocked(eps, id, func(ep *endpointsByNic) bool {
+		matchedEPs = append(matchedEPs, ep)
+		return true
+	})
 	return matchedEPs
 }
 
@@ -580,10 +584,12 @@ func (d *transportDemuxer) findTransportEndpoint(netProto tcpip.NetworkProtocolN
 // findEndpointLocked returns the endpoint that most closely matches the given
 // id.
 func (d *transportDemuxer) findEndpointLocked(eps *transportEndpoints, id TransportEndpointID) *endpointsByNic {
-	if matchedEPs := d.findAllEndpointsLocked(eps, id); len(matchedEPs) > 0 {
-		return matchedEPs[0]
-	}
-	return nil
+	var matchedEP *endpointsByNic
+	d.iterEndpointsLocked(eps, id, func(ep *endpointsByNic) bool {
+		matchedEP = ep
+		return false
+	})
+	return matchedEP
 }
 
 // registerRawEndpoint registers the given endpoint with the dispatcher such