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>

1 files changed, 17 insertions, 3 deletions

diff --git a/udp.c b/udp.c
index 7be88f6..edb73de 100644
--- a/udp.c
+++ b/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;
 		}
 	}