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

1 files changed, 30 insertions, 1 deletions

diff --git a/pkg/tcpip/link/rawfile/rawfile_unsafe.go b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
index be4a4fa9c..5deea093a 100644
--- a/pkg/tcpip/link/rawfile/rawfile_unsafe.go
+++ b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
@@ -124,7 +124,7 @@ func BlockingRead(fd int, b []byte) (int, *tcpip.Error) {
 
 // BlockingReadv reads from a file descriptor that is set up as non-blocking and
 // stores the data in a list of iovecs buffers. If no data is available, it will
-// block in a poll() syscall until the file descirptor becomes readable.
+// block in a poll() syscall until the file descriptor becomes readable.
 func BlockingReadv(fd int, iovecs []syscall.Iovec) (int, *tcpip.Error) {
 	for {
 		n, _, e := syscall.RawSyscall(syscall.SYS_READV, uintptr(fd), uintptr(unsafe.Pointer(&iovecs[0])), uintptr(len(iovecs)))
@@ -143,3 +143,32 @@ func BlockingReadv(fd int, iovecs []syscall.Iovec) (int, *tcpip.Error) {
 		}
 	}
 }
+
+// MMsgHdr represents the mmsg_hdr structure required by recvmmsg() on linux.
+type MMsgHdr struct {
+	Msg syscall.Msghdr
+	Len uint32
+	_   [4]byte
+}
+
+// BlockingRecvMMsg reads from a file descriptor that is set up as non-blocking
+// and stores the received messages in a slice of MMsgHdr structures. If no data
+// is available, it will block in a poll() syscall until the file descriptor
+// becomes readable.
+func BlockingRecvMMsg(fd int, msgHdrs []MMsgHdr) (int, *tcpip.Error) {
+	for {
+		n, _, e := syscall.RawSyscall6(syscall.SYS_RECVMMSG, uintptr(fd), uintptr(unsafe.Pointer(&msgHdrs[0])), uintptr(len(msgHdrs)), syscall.MSG_DONTWAIT, 0, 0)
+		if e == 0 {
+			return int(n), nil
+		}
+
+		event := pollEvent{
+			fd:     int32(fd),
+			events: 1, // POLLIN
+		}
+
+		if _, e := blockingPoll(&event, 1, -1); e != 0 && e != syscall.EINTR {
+			return 0, TranslateErrno(e)
+		}
+	}
+}