Use recvmmsg() instead of readv() to read packets from NIC.

This should reduce the number of syscalls required to process packets
significantly and improve throughputs.

PiperOrigin-RevId: 231366886
Change-Id: I8b38077262bf9c53176bc4a94b530188d3d7c0ca

3 files changed, 160 insertions, 31 deletions

diff --git a/pkg/tcpip/link/fdbased/BUILD b/pkg/tcpip/link/fdbased/BUILD
index 94391433c..a4aa3feec 100644
--- a/pkg/tcpip/link/fdbased/BUILD
+++ b/pkg/tcpip/link/fdbased/BUILD
@@ -27,6 +27,7 @@ go_test(
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/link/rawfile",
         "//pkg/tcpip/stack",
     ],
 )
diff --git a/pkg/tcpip/link/fdbased/endpoint.go b/pkg/tcpip/link/fdbased/endpoint.go
index 3a79d13d4..87c8ab1fc 100644
--- a/pkg/tcpip/link/fdbased/endpoint.go
+++ b/pkg/tcpip/link/fdbased/endpoint.go
@@ -24,6 +24,7 @@
 package fdbased
 
 import (
+	"fmt"
 	"syscall"
 
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
@@ -33,9 +34,19 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
 )
 
+const (
+	// MaxMsgsPerRecv is the maximum number of packets we want to retrieve
+	// in a single RecvMMsg call.
+	MaxMsgsPerRecv = 8
+)
+
 // BufConfig defines the shape of the vectorised view used to read packets from the NIC.
 var BufConfig = []int{128, 256, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768}
 
+// linkDispatcher reads packets from the link FD and dispatches them to the
+// NetworkDispatcher.
+type linkDispatcher func() (bool, *tcpip.Error)
+
 type endpoint struct {
 	// fd is the file descriptor used to send and receive packets.
 	fd int
@@ -57,14 +68,25 @@ type endpoint struct {
 	// its end of the communication pipe.
 	closed func(*tcpip.Error)
 
-	iovecs     []syscall.Iovec
-	views      []buffer.View
-	dispatcher stack.NetworkDispatcher
+	views             [][]buffer.View
+	iovecs            [][]syscall.Iovec
+	msgHdrs           []rawfile.MMsgHdr
+	inboundDispatcher linkDispatcher
+	dispatcher        stack.NetworkDispatcher
 
 	// handleLocal indicates whether packets destined to itself should be
 	// handled by the netstack internally (true) or be forwarded to the FD
 	// endpoint (false).
 	handleLocal bool
+
+	// useRecvMMsg enables use of recvmmsg() syscall instead of readv() to
+	// read inbound packets. This reduces # of syscalls needed to process
+	// packets.
+	//
+	// NOTE: recvmmsg() is only supported for sockets, so if the underlying
+	// FD is not a socket then the code will still fall back to the readv()
+	// path.
+	useRecvMMsg bool
 }
 
 // Options specify the details about the fd-based endpoint to be created.
@@ -78,6 +100,7 @@ type Options struct {
 	SaveRestore     bool
 	DisconnectOk    bool
 	HandleLocal     bool
+	UseRecvMMsg     bool
 }
 
 // New creates a new fd-based endpoint.
@@ -85,7 +108,10 @@ type Options struct {
 // Makes fd non-blocking, but does not take ownership of fd, which must remain
 // open for the lifetime of the returned endpoint.
 func New(opts *Options) tcpip.LinkEndpointID {
-	syscall.SetNonblock(opts.FD, true)
+	if err := syscall.SetNonblock(opts.FD, true); err != nil {
+		// TODO : replace panic with an error return.
+		panic(fmt.Sprintf("syscall.SetNonblock(%v) failed: %v", opts.FD, err))
+	}
 
 	caps := stack.LinkEndpointCapabilities(0)
 	if opts.ChecksumOffload {
@@ -113,13 +139,44 @@ func New(opts *Options) tcpip.LinkEndpointID {
 		closed:      opts.ClosedFunc,
 		addr:        opts.Address,
 		hdrSize:     hdrSize,
-		views:       make([]buffer.View, len(BufConfig)),
-		iovecs:      make([]syscall.Iovec, len(BufConfig)),
 		handleLocal: opts.HandleLocal,
+		useRecvMMsg: opts.UseRecvMMsg,
+	}
+	// For non-socket FDs we read one packet a time (e.g. TAP devices)
+	msgsPerRecv := 1
+	e.inboundDispatcher = e.dispatch
+	// If the provided FD is a socket then we optimize packet reads by
+	// using recvmmsg() instead of read() to read packets in a batch.
+	if isSocketFD(opts.FD) && e.useRecvMMsg {
+		e.inboundDispatcher = e.recvMMsgDispatch
+		msgsPerRecv = MaxMsgsPerRecv
+	}
+
+	e.views = make([][]buffer.View, msgsPerRecv)
+	for i, _ := range e.views {
+		e.views[i] = make([]buffer.View, len(BufConfig))
+	}
+	e.iovecs = make([][]syscall.Iovec, msgsPerRecv)
+	for i, _ := range e.iovecs {
+		e.iovecs[i] = make([]syscall.Iovec, len(BufConfig))
+	}
+	e.msgHdrs = make([]rawfile.MMsgHdr, msgsPerRecv)
+	for i, _ := range e.msgHdrs {
+		e.msgHdrs[i].Msg.Iov = &e.iovecs[i][0]
+		e.msgHdrs[i].Msg.Iovlen = uint64(len(BufConfig))
 	}
 	return stack.RegisterLinkEndpoint(e)
 }
 
+func isSocketFD(fd int) bool {
+	var stat syscall.Stat_t
+	if err := syscall.Fstat(fd, &stat); err != nil {
+		// TODO : replace panic with an error return.
+		panic(fmt.Sprintf("syscall.Fstat(%v,...) failed: %v", fd, err))
+	}
+	return (stat.Mode & syscall.S_IFSOCK) == syscall.S_IFSOCK
+}
+
 // Attach launches the goroutine that reads packets from the file descriptor and
 // dispatches them via the provided dispatcher.
 func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
@@ -191,12 +248,12 @@ func (e *endpoint) WritePacket(r *stack.Route, hdr buffer.Prependable, payload b
 	return rawfile.NonBlockingWrite2(e.fd, hdr.View(), payload.ToView())
 }
 
-func (e *endpoint) capViews(n int, buffers []int) int {
+func (e *endpoint) capViews(k, n int, buffers []int) int {
 	c := 0
 	for i, s := range buffers {
 		c += s
 		if c >= n {
-			e.views[i].CapLength(s - (c - n))
+			e.views[k][i].CapLength(s - (c - n))
 			return i + 1
 		}
 	}
@@ -204,24 +261,26 @@ func (e *endpoint) capViews(n int, buffers []int) int {
 }
 
 func (e *endpoint) allocateViews(bufConfig []int) {
-	for i, v := range e.views {
-		if v != nil {
-			break
-		}
-		b := buffer.NewView(bufConfig[i])
-		e.views[i] = b
-		e.iovecs[i] = syscall.Iovec{
-			Base: &b[0],
-			Len:  uint64(len(b)),
+	for k := 0; k < len(e.views); k++ {
+		for i := 0; i < len(bufConfig); i++ {
+			if e.views[k][i] != nil {
+				break
+			}
+			b := buffer.NewView(bufConfig[i])
+			e.views[k][i] = b
+			e.iovecs[k][i] = syscall.Iovec{
+				Base: &b[0],
+				Len:  uint64(len(b)),
+			}
 		}
 	}
 }
 
 // dispatch reads one packet from the file descriptor and dispatches it.
-func (e *endpoint) dispatch(largeV buffer.View) (bool, *tcpip.Error) {
+func (e *endpoint) dispatch() (bool, *tcpip.Error) {
 	e.allocateViews(BufConfig)
 
-	n, err := rawfile.BlockingReadv(e.fd, e.iovecs)
+	n, err := rawfile.BlockingReadv(e.fd, e.iovecs[0])
 	if err != nil {
 		return false, err
 	}
@@ -235,14 +294,14 @@ func (e *endpoint) dispatch(largeV buffer.View) (bool, *tcpip.Error) {
 		remote, local tcpip.LinkAddress
 	)
 	if e.hdrSize > 0 {
-		eth := header.Ethernet(e.views[0])
+		eth := header.Ethernet(e.views[0][0])
 		p = eth.Type()
 		remote = eth.SourceAddress()
 		local = eth.DestinationAddress()
 	} else {
 		// We don't get any indication of what the packet is, so try to guess
 		// if it's an IPv4 or IPv6 packet.
-		switch header.IPVersion(e.views[0]) {
+		switch header.IPVersion(e.views[0][0]) {
 		case header.IPv4Version:
 			p = header.IPv4ProtocolNumber
 		case header.IPv6Version:
@@ -252,15 +311,71 @@ func (e *endpoint) dispatch(largeV buffer.View) (bool, *tcpip.Error) {
 		}
 	}
 
-	used := e.capViews(n, BufConfig)
-	vv := buffer.NewVectorisedView(n, e.views[:used])
+	used := e.capViews(0, n, BufConfig)
+	vv := buffer.NewVectorisedView(n, e.views[0][:used])
 	vv.TrimFront(e.hdrSize)
 
 	e.dispatcher.DeliverNetworkPacket(e, remote, local, p, vv)
 
 	// Prepare e.views for another packet: release used views.
 	for i := 0; i < used; i++ {
-		e.views[i] = nil
+		e.views[0][i] = nil
+	}
+
+	return true, nil
+}
+
+// recvMMsgDispatch reads more than one packet at a time from the file
+// descriptor and dispatches it.
+func (e *endpoint) recvMMsgDispatch() (bool, *tcpip.Error) {
+	e.allocateViews(BufConfig)
+
+	nMsgs, err := rawfile.BlockingRecvMMsg(e.fd, e.msgHdrs)
+	if err != nil {
+		return false, err
+	}
+	// Process each of received packets.
+	for k := 0; k < nMsgs; k++ {
+		n := e.msgHdrs[k].Len
+		if n <= uint32(e.hdrSize) {
+			return false, nil
+		}
+
+		var (
+			p             tcpip.NetworkProtocolNumber
+			remote, local tcpip.LinkAddress
+		)
+		if e.hdrSize > 0 {
+			eth := header.Ethernet(e.views[k][0])
+			p = eth.Type()
+			remote = eth.SourceAddress()
+			local = eth.DestinationAddress()
+		} else {
+			// We don't get any indication of what the packet is, so try to guess
+			// if it's an IPv4 or IPv6 packet.
+			switch header.IPVersion(e.views[k][0]) {
+			case header.IPv4Version:
+				p = header.IPv4ProtocolNumber
+			case header.IPv6Version:
+				p = header.IPv6ProtocolNumber
+			default:
+				return true, nil
+			}
+		}
+
+		used := e.capViews(k, int(n), BufConfig)
+		vv := buffer.NewVectorisedView(int(n), e.views[k][:used])
+		vv.TrimFront(e.hdrSize)
+		e.dispatcher.DeliverNetworkPacket(e, remote, local, p, vv)
+
+		// Prepare e.views for another packet: release used views.
+		for i := 0; i < used; i++ {
+			e.views[k][i] = nil
+		}
+	}
+
+	for k := 0; k < nMsgs; k++ {
+		e.msgHdrs[k].Len = 0
 	}
 
 	return true, nil
@@ -269,9 +384,8 @@ func (e *endpoint) dispatch(largeV buffer.View) (bool, *tcpip.Error) {
 // dispatchLoop reads packets from the file descriptor in a loop and dispatches
 // them to the network stack.
 func (e *endpoint) dispatchLoop() *tcpip.Error {
-	v := buffer.NewView(header.MaxIPPacketSize)
 	for {
-		cont, err := e.dispatch(v)
+		cont, err := e.inboundDispatcher()
 		if err != nil || !cont {
 			if e.closed != nil {
 				e.closed(err)
diff --git a/pkg/tcpip/link/fdbased/endpoint_test.go b/pkg/tcpip/link/fdbased/endpoint_test.go
index 226639443..14abacdf2 100644
--- a/pkg/tcpip/link/fdbased/endpoint_test.go
+++ b/pkg/tcpip/link/fdbased/endpoint_test.go
@@ -28,6 +28,7 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/link/rawfile"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
 )
 
@@ -309,9 +310,22 @@ func TestBufConfigFirst(t *testing.T) {
 
 func build(bufConfig []int) *endpoint {
 	e := &endpoint{
-		views:  make([]buffer.View, len(bufConfig)),
-		iovecs: make([]syscall.Iovec, len(bufConfig)),
+		views:   make([][]buffer.View, MaxMsgsPerRecv),
+		iovecs:  make([][]syscall.Iovec, MaxMsgsPerRecv),
+		msgHdrs: make([]rawfile.MMsgHdr, MaxMsgsPerRecv),
 	}
+
+	for i, _ := range e.views {
+		e.views[i] = make([]buffer.View, len(bufConfig))
+	}
+	for i := range e.iovecs {
+		e.iovecs[i] = make([]syscall.Iovec, len(bufConfig))
+	}
+	for k, msgHdr := range e.msgHdrs {
+		msgHdr.Msg.Iov = &e.iovecs[k][0]
+		msgHdr.Msg.Iovlen = uint64(len(bufConfig))
+	}
+
 	e.allocateViews(bufConfig)
 	return e
 }
@@ -356,12 +370,12 @@ var capLengthTestCases = []struct {
 func TestCapLength(t *testing.T) {
 	for _, c := range capLengthTestCases {
 		e := build(c.config)
-		used := e.capViews(c.n, c.config)
+		used := e.capViews(0, c.n, c.config)
 		if used != c.wantUsed {
 			t.Errorf("Test \"%s\" failed when calling capViews(%d, %v). Got %d. Want %d", c.comment, c.n, c.config, used, c.wantUsed)
 		}
-		lengths := make([]int, len(e.views))
-		for i, v := range e.views {
+		lengths := make([]int, len(e.views[0]))
+		for i, v := range e.views[0] {
 			lengths[i] = len(v)
 		}
 		if !reflect.DeepEqual(lengths, c.wantLengths) {