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passt: Spare some syscalls, add some optimisations from profiling

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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>
This commit is contained in:
Stefano Brivio 2021-04-23 22:22:37 +02:00
parent 962bc97cf1
commit 38b50dba47
10 changed files with 139 additions and 49 deletions

113
passt.c
View file

@ -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);