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dpif-linux: Use poll() internally in dpif_linux_recv().

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Using poll() internally in dpif_linux_recv(), instead of relying
on the results of the main loop poll() call, brings netperf CRR
performance back within 1% of par versus the code base before the
poll_fd_woke() optimizations were introduced.  It also increases
the ovs-benchmark results by about 5% versus that baseline, too.

My theory is that this is because the main loop takes long enough
that a significant number of packets can arrive during the main
loop itself, so this reduces the time before OVS gets to those
packets.
This commit is contained in:
Ben Pfaff
2011-11-28 09:29:18 -08:00
parent 3907401ce6
commit 8522ba0996
3 changed files with 56 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

52
lib/dpif-linux.c
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@@ -28,7 +28,9 @@
#include <linux/pkt_sched.h>
#include <linux/rtnetlink.h>
#include <linux/sockios.h>
#include <poll.h>
#include <stdlib.h>
#include <strings.h>
#include <sys/stat.h>
#include <unistd.h>
@@ -63,6 +65,7 @@ BUILD_ASSERT_DECL(IS_POW2(LRU_MAX_PORTS));
enum { N_UPCALL_SOCKS = 16 };
BUILD_ASSERT_DECL(IS_POW2(N_UPCALL_SOCKS));
BUILD_ASSERT_DECL(N_UPCALL_SOCKS <= 32); /* We use a 32-bit word as a mask. */
/* This ethtool flag was introduced in Linux 2.6.24, so it might be
* missing if we have old headers. */
@@ -135,8 +138,8 @@ struct dpif_linux {
/* Upcall messages. */
struct nl_sock *upcall_socks[N_UPCALL_SOCKS];
int last_read_upcall;
unsigned int listen_mask;
uint32_t ready_mask; /* 1-bit for each sock with unread messages. */
unsigned int listen_mask; /* Mask of DPIF_UC_* bits. */
/* Change notification. */
struct sset changed_ports; /* Ports that have changed. */
@@ -1009,6 +1012,8 @@ dpif_linux_recv_set_mask(struct dpif *dpif_, int listen_mask)
return error;
}
}
dpif->ready_mask = 0;
}
dpif->listen_mask = listen_mask;
@@ -1088,24 +1093,51 @@ static int
dpif_linux_recv(struct dpif *dpif_, struct dpif_upcall *upcall)
{
struct dpif_linux *dpif = dpif_linux_cast(dpif_);
int i;
int read_tries = 0;
if (!dpif->listen_mask) {
return EAGAIN;
}
for (i = 0; i < N_UPCALL_SOCKS; i++) {
struct nl_sock *upcall_sock;
int dp_ifindex;
if (!dpif->ready_mask) {
struct pollfd pfds[N_UPCALL_SOCKS];
int retval;
int i;
dpif->last_read_upcall = (dpif->last_read_upcall + 1) &
(N_UPCALL_SOCKS - 1);
upcall_sock = dpif->upcall_socks[dpif->last_read_upcall];
for (i = 0; i < N_UPCALL_SOCKS; i++) {
pfds[i].fd = nl_sock_fd(dpif->upcall_socks[i]);
pfds[i].events = POLLIN;
pfds[i].revents = 0;
}
do {
retval = poll(pfds, N_UPCALL_SOCKS, 0);
} while (retval < 0 && errno == EINTR);
if (retval < 0) {
static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
VLOG_WARN_RL(&rl, "poll failed (%s)", strerror(errno));
} else if (!retval) {
return EAGAIN;
}
for (i = 0; i < N_UPCALL_SOCKS; i++) {
if (pfds[i].revents) {
dpif->ready_mask |= 1u << i;
}
}
assert(dpif->ready_mask);
}
do {
int indx = ffs(dpif->ready_mask) - 1;
struct nl_sock *upcall_sock = dpif->upcall_socks[indx];
dpif->ready_mask &= ~(1u << indx);
for (;;) {
struct ofpbuf *buf;
int dp_ifindex;
int error;
if (++read_tries > 50) {
@@ -1131,7 +1163,7 @@ dpif_linux_recv(struct dpif *dpif_, struct dpif_upcall *upcall)
return error;
}
}
}
} while (dpif->ready_mask);
return EAGAIN;
}