[ovs-dev] [threads v2 04/13] poll-loop: Simplify and speed up polling.
Gurucharan Shetty
shettyg at nicira.com
Tue Jul 16 17:41:25 UTC 2013
On Fri, Jul 12, 2013 at 2:54 PM, Ben Pfaff <blp at nicira.com> wrote:
> 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'. */
>
The comment needs an update as we no longer return anything.
-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 4c488ee..6c78bbd 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
>
Looks good to me.
> --
> 1.7.2.5
>
> _______________________________________________
> dev mailing list
> dev at openvswitch.org
> http://openvswitch.org/mailman/listinfo/dev
>
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