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, 15 insertions, 0 deletions

diff --git a/util.c b/util.c
index 7a75e02..cc96a1a 100644
--- a/util.c
+++ b/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;