passt: Spare some syscalls, add some optimisations from profiling

Avoid a bunch of syscalls on forwarding paths by:

- storing minimum and maximum file descriptor numbers for each
  protocol, fall back to SO_PROTOCOL query only on overlaps

- allocating a larger receive buffer -- this can result in more
  coalesced packets than sendmmsg() can take (UIO_MAXIOV, i.e. 1024),
  so make sure we don't exceed that within a single call to protocol
  tap handlers

- nesting the handling loop in tap_handler() in the receive loop,
  so that we have better chances of filling our receive buffer in
  fewer calls

- skipping the recvfrom() in the UDP handler on EPOLLERR -- there's
  nothing to be done in that case

and while at it:

- restore the 20ms timer interval for periodic (TCP) events, I
  accidentally changed that to 100ms in an earlier commit

- attempt using SO_ZEROCOPY for UDP -- if it's not available,
  sendmmsg() will succeed anyway

- fix the handling of the status code from sendmmsg(), if it fails,
  we'll try to discard the first message, hence return 1 from the
  UDP handler

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

icmp.c

@@ -135,6 +135,9 @@ int icmp_tap_handler(struct ctx *c, int af, void *addr,
  */
 int icmp_sock_init(struct ctx *c)
 {
+	c->icmp.fd_min = INT_MAX;
+	c->icmp.fd_max = 0;
+
 	if (c->v4 && (c->icmp.s4 = sock_l4_add(c, 4, IPPROTO_ICMP, 0)) < 0)
 		return -1;
 

icmp.h

@@ -12,10 +12,14 @@ int icmp_sock_init(struct ctx *c);
  * struct icmp_ctx - Execution context for ICMP routines
  * @s4:		ICMP socket number
  * @s6:		ICMPv6 socket number
+ * @fd_min:	Lowest file descriptor number for ICMP/ICMPv6 ever used
+ * @fd_max:	Highest file descriptor number for ICMP/ICMPv6 ever used
  */
 struct icmp_ctx {
 	int s4;
 	int s6;
+	int fd_min;
+	int fd_max;
 };
 
 #endif /* ICMP_H */

passt.c

@@ -57,9 +57,11 @@
 
 #define EPOLL_EVENTS		10
 
-#define TAP_NMSG		32  /* maximum messages to buffer from tap */
+#define TAP_BUF_BYTES		(ETH_MAX_MTU * 8)
+#define TAP_BUF_FILL		(TAP_BUF_BYTES - ETH_MAX_MTU - sizeof(uint32_t))
+#define TAP_MSGS		(TAP_BUF_BYTES / sizeof(struct ethhdr) + 1)
 
-#define TIMER_INTERVAL		100 /* ms, for protocol periodic handlers */
+#define TIMER_INTERVAL		20 /* ms, for protocol periodic handlers */
 
 /**
  * sock_unix() - Create and bind AF_UNIX socket, add to epoll list
@@ -515,7 +517,7 @@ static int tap6_handler(struct ctx *c, struct tap_msg *msg, size_t count)
 	return 1;
 }
 
-static char tap_buf[ETH_MAX_MTU * TAP_NMSG];
+static char tap_buf[TAP_BUF_BYTES];
 
 /**
  * tap_handler() - Packet handler for tap file descriptor
@@ -525,32 +527,30 @@ static char tap_buf[ETH_MAX_MTU * TAP_NMSG];
  */
 static int tap_handler(struct ctx *c)
 {
-	int msg_count = 0, same, rcv = 0, i = 0;
-	struct tap_msg msg[UIO_MAXIOV];
-	ssize_t n, rem, fill;
+	struct tap_msg msg[TAP_MSGS];
+	int msg_count, same, i;
 	struct ethhdr *eh;
 	char *p = tap_buf;
+	ssize_t n, rem;
 
-	fill = ETH_MAX_MTU * (TAP_NMSG - 1);
+	while ((n = recv(c->fd_unix, p, TAP_BUF_FILL, MSG_DONTWAIT)) > 0) {
+		msg_count = 0;
 
-	while ((n = recv(c->fd_unix, p, fill, MSG_DONTWAIT)) > 0) {
-		fill -= n;
-		while (n > 0) {
+		while (n > (ssize_t)sizeof(uint32_t)) {
 			ssize_t len = ntohl(*(uint32_t *)p);
 
 			p += sizeof(uint32_t);
 			n -= sizeof(uint32_t);
 
 			if (len < (ssize_t)sizeof(*eh))
-				break;
+				return 0;
 
 			/* At most one packet might not fit in a single read */
 			if (len > n) {
-				rem = recv(c->fd_unix, p + n, fill,
+				rem = recv(c->fd_unix, p + n, len - n,
 					   MSG_DONTWAIT);
-				rcv = errno;
-				if (rem <= 0 || rem + n != len)
-					break;
+				if ((n += rem) != len)
+					return 0;
 			}
 
 			msg[msg_count].start = p;
@@ -559,40 +559,49 @@ static int tap_handler(struct ctx *c)
 			n -= len;
 			p += len;
 		}
-	}
 
-	rcv = errno;
-
-	while (i < msg_count) {
-		eh = (struct ethhdr *)msg[i].start;
+		i = 0;
+		while (i < msg_count) {
+			eh = (struct ethhdr *)msg[i].start;
 			switch (ntohs(eh->h_proto)) {
-		case ETH_P_ARP:
-			tap4_handler(c, msg + i, 1);
-			i++;
-			break;
-		case ETH_P_IP:
-			for (same = 1; i + same < msg_count; same++) {
-				eh = (struct ethhdr *)msg[i + same].start;
-				if (ntohs(eh->h_proto) != ETH_P_IP)
-					break;
-			}
+			case ETH_P_ARP:
+				tap4_handler(c, msg + i, 1);
+				i++;
+				break;
+			case ETH_P_IP:
+				for (same = 1; i + same < msg_count &&
+					       same < UIO_MAXIOV; same++) {
+					struct tap_msg *next = &msg[i + same];
+
+					eh = (struct ethhdr *)next->start;
+					if (ntohs(eh->h_proto) != ETH_P_IP)
+						break;
+				}
+
 				i += tap4_handler(c, msg + i, same);
-			break;
-		case ETH_P_IPV6:
-			for (same = 1; i + same < msg_count; same++) {
-				eh = (struct ethhdr *)msg[i + same].start;
-				if (ntohs(eh->h_proto) != ETH_P_IPV6)
-					break;
-			}
+				break;
+			case ETH_P_IPV6:
+				for (same = 1; i + same < msg_count &&
+					       same < UIO_MAXIOV; same++) {
+					struct tap_msg *next = &msg[i + same];
+
+					eh = (struct ethhdr *)next->start;
+					if (ntohs(eh->h_proto) != ETH_P_IPV6)
+						break;
+				}
+
 				i += tap6_handler(c, msg + i, same);
-			break;
-		default:
-			i++;
-			break;
+				break;
+			default:
+				i++;
+				break;
+			}
 		}
+
+		p = tap_buf;
 	}
 
-	if (n >= 0 || rcv == EINTR || rcv == EAGAIN || rcv == EWOULDBLOCK)
+	if (n >= 0 || errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK)
 		return 0;
 
 	epoll_ctl(c->epollfd, EPOLL_CTL_DEL, c->fd_unix, NULL);
@@ -614,8 +623,21 @@ static void sock_handler(struct ctx *c, int fd, uint32_t events)
 
 	sl = sizeof(so);
 
-	if (getsockopt(fd, SOL_SOCKET, SO_PROTOCOL, &so, &sl))
+#define IN(x, proto)	(x >= c->proto.fd_min && x <= c->proto.fd_max)
+
+	if (IN(fd, udp)		&& !IN(fd, icmp)	&& !IN(fd, tcp))
+		so = IPPROTO_UDP;
+	else if (IN(fd, tcp)	&& !IN(fd, icmp)	&& !IN(fd, udp))
+		so = IPPROTO_TCP;
+	else if (IN(fd, icmp)	&& !IN(fd, udp)		&& !IN(fd, tcp))
+		so = IPPROTO_ICMP;	/* Fits ICMPv6 below, too */
+	else if (getsockopt(fd, SOL_SOCKET, SO_PROTOCOL, &so, &sl)) {
+		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, fd, NULL);
+		close(fd);
 		return;
+	}
+
+#undef IN
 
 	debug("%s: packet from socket %i", getprotobynumber(so)->p_name, fd);
 
@@ -771,7 +793,10 @@ loop:
 
 	for (i = 0; i < nfds; i++) {
 		if (events[i].data.fd == c.fd_unix) {
-			if (tap_handler(&c))
+			if (events[i].events	& EPOLLRDHUP	||
+			    events[i].events	& EPOLLHUP	||
+			    events[i].events	& EPOLLERR	||
+			    tap_handler(&c))
 				goto listen;
 		} else {
 			sock_handler(&c, events[i].data.fd, events[i].events);

passt.h

@@ -16,6 +16,7 @@ struct tap_msg {
 
 #include "icmp.h"
 #include "tcp.h"
+#include "udp.h"
 
 /**
  * struct ctx - Execution context
@@ -56,4 +57,5 @@ struct ctx {
 
 	struct icmp_ctx icmp;
 	struct tcp_ctx tcp;
+	struct tcp_ctx udp;
 };

tap.c

@@ -37,9 +37,9 @@
 int tap_send(int fd, void *data, size_t len, int flags)
 {
 	uint32_t vnet_len = htonl(len);
-	send(fd, &vnet_len, 4, 0);
+	send(fd, &vnet_len, 4, MSG_DONTWAIT | MSG_NOSIGNAL);
 
-	return send(fd, data, len, flags);
+	return send(fd, data, len, flags | MSG_DONTWAIT | MSG_NOSIGNAL);
 }
 
 /**

tcp.c

@@ -1003,6 +1003,11 @@ static void tcp_conn_from_sock(struct ctx *c, int fd)
 	if (s == -1)
 		return;
 
+	if (s < c->tcp.fd_min)
+		c->tcp.fd_min = s;
+	if (s > c->tcp.fd_max)
+		c->tcp.fd_max = s;
+
 	if (sa_l.ss_family == AF_INET) {
 		struct sockaddr_in *sa4 = (struct sockaddr_in *)&sa_r;
 
@@ -1445,6 +1450,9 @@ int tcp_sock_init(struct ctx *c)
 {
 	in_port_t port;
 
+	c->tcp.fd_min = INT_MAX;
+	c->tcp.fd_max = 0;
+
 	for (port = 0; port < (1 << 15) + (1 << 14); port++) {
 		if (c->v4 && sock_l4_add(c, 4, IPPROTO_TCP, port) < 0)
 			return -1;

tcp.h

@@ -12,9 +12,13 @@ void tcp_timer(struct ctx *c, struct timespec *ts);
 /**
  * struct tcp_ctx - Execution context for TCP routines
  * @hash_secret:	128-bit secret for hash functions, ISN and hash table
+ * @fd_min:		Lowest file descriptor number for TCP ever used
+ * @fd_max:		Highest file descriptor number for TCP ever used
  */
 struct tcp_ctx {
 	uint64_t hash_secret[2];
+	int fd_min;
+	int fd_max;
 };
 
 #endif /* TCP_H */

udp.c

@@ -68,7 +68,8 @@ void udp_sock_handler(struct ctx *c, int s, uint32_t events)
 	struct udphdr *uh;
 	ssize_t n;
 
-	(void)events;
+	if (events == EPOLLERR)
+		return;
 
 	n = recvfrom(s, buf + sizeof(*uh), sizeof(buf) - sizeof(*uh),
 		     MSG_DONTWAIT, (struct sockaddr *)&sr, &slen);
@@ -179,7 +180,11 @@ int udp_tap_handler(struct ctx *c, int af, void *addr,
 		return count;
 	}
 
-	return sendmmsg(s, mm, count, MSG_DONTWAIT | MSG_NOSIGNAL);
+	count = sendmmsg(s, mm, count, MSG_DONTWAIT | MSG_NOSIGNAL | MSG_ZEROCOPY);
+	if (count < 0)
+		return 1;
+
+	return count;
 }
 
 /**
@@ -191,13 +196,19 @@ int udp_tap_handler(struct ctx *c, int af, void *addr,
 int udp_sock_init(struct ctx *c)
 {
 	in_port_t port;
-	int s;
+	int s, one = 1;
+
+	c->udp.fd_min = INT_MAX;
+	c->udp.fd_max = 0;
 
 	for (port = 0; port < USHRT_MAX; port++) {
 		if (c->v4) {
 			if ((s = sock_l4_add(c, 4, IPPROTO_UDP, port)) < 0)
 				return -1;
 
+			setsockopt(s, SOL_SOCKET, SO_ZEROCOPY,
+				   &one, sizeof(one));
+
 			udp4_sock_port[port] = s;
 		}
 
@@ -205,6 +216,9 @@ int udp_sock_init(struct ctx *c)
 			if ((s = sock_l4_add(c, 6, IPPROTO_UDP, port)) < 0)
 				return -1;
 
+			setsockopt(s, SOL_SOCKET, SO_ZEROCOPY,
+				   &one, sizeof(one));
+
 			udp6_sock_port[port] = s;
 		}
 	}

udp.h

@@ -1,4 +1,19 @@
+#ifndef UDP_H
+#define UDP_H
+
 void udp_sock_handler(struct ctx *c, int s, uint32_t events);
 int udp_tap_handler(struct ctx *c, int af, void *addr,
 		    struct tap_msg *msg, int count);
 int udp_sock_init(struct ctx *c);
+
+/**
+ * struct udp_ctx - Execution context for UDP
+ * @fd_min:		Lowest file descriptor number for UDP ever used
+ * @fd_max:		Highest file descriptor number for UDP ever used
+ */
+struct udp_ctx {
+	int fd_min;
+	int fd_max;
+};
+
+#endif /* UDP_H */

util.c

@@ -189,6 +189,21 @@ int sock_l4_add(struct ctx *c, int v, uint16_t proto, uint16_t port)
 		return -1;
 	}
 
+#define CHECK_SET_MIN_MAX(ipproto, proto_ctx, fd)			\
+	if (proto == (ipproto)) {					\
+		if (fd < c->proto_ctx.fd_min)				\
+			c->proto_ctx.fd_min = (fd);			\
+		if (fd > c->proto_ctx.fd_max)				\
+			c->proto_ctx.fd_max = (fd);			\
+	}
+
+	CHECK_SET_MIN_MAX(IPPROTO_ICMP,		icmp,	fd);
+	CHECK_SET_MIN_MAX(IPPROTO_ICMPV6,	icmp,	fd);
+	CHECK_SET_MIN_MAX(IPPROTO_TCP,		tcp,	fd);
+	CHECK_SET_MIN_MAX(IPPROTO_UDP,		udp,	fd);
+
+#undef CHECK_SET_MIN_MAX
+
 	if (proto == IPPROTO_ICMP || proto == IPPROTO_ICMPV6)
 		goto epoll_add;