[ovs-dev] [threads 11/28] poll-loop: Simplify and speed up polling.
Ben Pfaff
blp at nicira.com
Wed Jul 10 23:03:53 UTC 2013
The simplification comes from dropping support for canceling a
poll_waiter, which was a feature that was never used. The speedup
comes from avoiding a malloc() for every call to poll_fd_wait().
(I doubt that this significantly improves performance.)
This prepares for making the polling structures per-thread in
the next commit.
Signed-off-by: Ben Pfaff <blp at nicira.com>
---
lib/poll-loop.c | 85 +++++++++++++++---------------------------------------
lib/poll-loop.h | 6 +---
2 files changed, 25 insertions(+), 66 deletions(-)
diff --git a/lib/poll-loop.c b/lib/poll-loop.c
index 5f4b16c..567c19f 100644
--- a/lib/poll-loop.c
+++ b/lib/poll-loop.c
@@ -41,18 +41,13 @@ COVERAGE_DEFINE(poll_zero_timeout);
/* An event that will wake the following call to poll_block(). */
struct poll_waiter {
- /* Set when the waiter is created. */
- struct list node; /* Element in global waiters list. */
- int fd; /* File descriptor. */
- short int events; /* Events to wait for (POLLIN, POLLOUT). */
const char *where; /* Where the waiter was created. */
-
- /* Set only when poll_block() is called. */
- struct pollfd *pollfd; /* Pointer to element of the pollfds array. */
};
/* All active poll waiters. */
-static struct list waiters = LIST_INITIALIZER(&waiters);
+static struct poll_waiter *waiters;
+static struct pollfd *pollfds;
+static size_t n_waiters, allocated_waiters;
/* Time at which to wake up the next call to poll_block(), in milliseconds as
* returned by time_msec(), LLONG_MIN to wake up immediately, or LLONG_MAX to
@@ -62,8 +57,7 @@ static long long int timeout_when = LLONG_MAX;
/* Location where waiter created. */
static const char *timeout_where;
-static struct poll_waiter *new_waiter(int fd, short int events,
- const char *where);
+static void new_waiter(int fd, short int events, const char *where);
/* Registers 'fd' as waiting for the specified 'events' (which should be POLLIN
* or POLLOUT or POLLIN | POLLOUT). The following call to poll_block() will
@@ -75,11 +69,11 @@ static struct poll_waiter *new_waiter(int fd, short int events,
*
* Ordinarily the 'where' argument is supplied automatically; see poll-loop.h
* for more information. */
-struct poll_waiter *
+void
poll_fd_wait(int fd, short int events, const char *where)
{
COVERAGE_INC(poll_fd_wait);
- return new_waiter(fd, events, where);
+ new_waiter(fd, events, where);
}
/* Causes the following call to poll_block() to block for no more than 'msec'
@@ -210,11 +204,6 @@ log_wakeup(const char *where, const struct pollfd *pollfd, int timeout)
void
poll_block(void)
{
- static struct pollfd *pollfds;
- static size_t max_pollfds;
-
- struct poll_waiter *pw, *next;
- int n_waiters, n_pollfds;
int elapsed;
int retval;
@@ -222,70 +211,44 @@ poll_block(void)
* poll_block. */
fatal_signal_wait();
- n_waiters = list_size(&waiters);
- if (max_pollfds < n_waiters) {
- max_pollfds = n_waiters;
- pollfds = xrealloc(pollfds, max_pollfds * sizeof *pollfds);
- }
-
- n_pollfds = 0;
- LIST_FOR_EACH (pw, node, &waiters) {
- pw->pollfd = &pollfds[n_pollfds];
- pollfds[n_pollfds].fd = pw->fd;
- pollfds[n_pollfds].events = pw->events;
- pollfds[n_pollfds].revents = 0;
- n_pollfds++;
- }
-
if (timeout_when == LLONG_MIN) {
COVERAGE_INC(poll_zero_timeout);
}
- retval = time_poll(pollfds, n_pollfds, timeout_when, &elapsed);
+ retval = time_poll(pollfds, n_waiters, timeout_when, &elapsed);
if (retval < 0) {
static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
VLOG_ERR_RL(&rl, "poll: %s", ovs_strerror(-retval));
} else if (!retval) {
log_wakeup(timeout_where, NULL, elapsed);
- }
+ } else if (get_cpu_usage() > 50 || VLOG_IS_DBG_ENABLED()) {
+ size_t i;
- LIST_FOR_EACH_SAFE (pw, next, node, &waiters) {
- if (pw->pollfd->revents) {
- log_wakeup(pw->where, pw->pollfd, 0);
+ for (i = 0; i < n_waiters; i++) {
+ if (pollfds[i].revents) {
+ log_wakeup(waiters[i].where, &pollfds[i], 0);
+ }
}
- poll_cancel(pw);
}
timeout_when = LLONG_MAX;
timeout_where = NULL;
+ n_waiters = 0;
/* Handle any pending signals before doing anything else. */
fatal_signal_run();
}
-
-/* Cancels the file descriptor event registered with poll_fd_wait() using 'pw',
- * the struct poll_waiter returned by that function.
- *
- * An event registered with poll_fd_wait() may be canceled from its time of
- * registration until the next call to poll_block(). At that point, the event
- * is automatically canceled by the system and its poll_waiter is freed. */
-void
-poll_cancel(struct poll_waiter *pw)
-{
- if (pw) {
- list_remove(&pw->node);
- free(pw);
- }
-}
/* Creates and returns a new poll_waiter for 'fd' and 'events'. */
-static struct poll_waiter *
+static void
new_waiter(int fd, short int events, const char *where)
{
- struct poll_waiter *waiter = xzalloc(sizeof *waiter);
- ovs_assert(fd >= 0);
- waiter->fd = fd;
- waiter->events = events;
- waiter->where = where;
- list_push_back(&waiters, &waiter->node);
- return waiter;
+ if (n_waiters >= allocated_waiters) {
+ waiters = x2nrealloc(waiters, &allocated_waiters, sizeof *waiters);
+ pollfds = xrealloc(pollfds, allocated_waiters * sizeof *pollfds);
+ }
+
+ waiters[n_waiters].where = where;
+ pollfds[n_waiters].fd = fd;
+ pollfds[n_waiters].events = events;
+ n_waiters++;
}
diff --git a/lib/poll-loop.h b/lib/poll-loop.h
index e77d027..befaf14 100644
--- a/lib/poll-loop.h
+++ b/lib/poll-loop.h
@@ -34,7 +34,6 @@
extern "C" {
#endif
-struct poll_waiter;
/* Schedule events to wake up the following poll_block().
*
@@ -47,7 +46,7 @@ struct poll_waiter;
* (poll_fd_wait)(fd, events, where);
* See timer_wait() for an example.
*/
-struct poll_waiter *poll_fd_wait(int fd, short int events, const char *where);
+void poll_fd_wait(int fd, short int events, const char *where);
#define poll_fd_wait(fd, events) poll_fd_wait(fd, events, SOURCE_LOCATOR)
void poll_timer_wait(long long int msec, const char *where);
@@ -62,9 +61,6 @@ void poll_immediate_wake(const char *where);
/* Wait until an event occurs. */
void poll_block(void);
-/* Cancel a file descriptor callback or event. */
-void poll_cancel(struct poll_waiter *);
-
#ifdef __cplusplus
}
#endif
--
1.7.2.5
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