On 2014-11-05 00:26, Peter Meerwald wrote:
> From: Peter Meerwald <p.meerwald at bct-electronic.com>
>
> when the wakeup pipe became ready, and poll() returned
> just one descriptor, we can stop scanning io_events
Eh, does this really make things faster?
Right now it seems to add another syscall - with the patch, we call
clear_wakeup -> pa_read -> read syscall twice per iteration, once from
dispatch_pollfds and once from pa_mainloop_prepare.
In addition, I don't see anything particular time consuming in looping
through a few io_events.
Replacing the wakeup pipe with a pa_fdsem would be an interesting
optimisation though, as pa_fdsem has a few atomic operations to avoid
the entire write-poll-read cycle if no thread is currently waiting for
the fdsem.
>
> Signed-off-by: Peter Meerwald <pmeerw at pmeerw.net>
> ---
> src/pulse/mainloop.c | 24 ++++++++++++++----------
> 1 file changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/src/pulse/mainloop.c b/src/pulse/mainloop.c
> index c7a5236..a7a3c48 100644
> --- a/src/pulse/mainloop.c
> +++ b/src/pulse/mainloop.c
> @@ -635,6 +635,15 @@ static void rebuild_pollfds(pa_mainloop *m) {
> m->rebuild_pollfds = false;
> }
>
> +static void clear_wakeup(pa_mainloop *m) {
> + char c[10];
> +
> + pa_assert(m);
> +
> + while (pa_read(m->wakeup_pipe[0], &c, sizeof(c), &m->wakeup_pipe_type) == sizeof(c))
> + ;
> +}
> +
> static unsigned dispatch_pollfds(pa_mainloop *m) {
> pa_io_event *e;
> unsigned r = 0, k;
> @@ -642,6 +651,11 @@ static unsigned dispatch_pollfds(pa_mainloop *m) {
> pa_assert(m->poll_func_ret > 0);
>
> k = m->poll_func_ret;
> + if (m->pollfds[0].revents) {
> + clear_wakeup(m);
> + m->pollfds[0].revents = 0;
> + k--;
> + }
>
> PA_LLIST_FOREACH(e, m->io_events) {
>
> @@ -775,20 +789,10 @@ void pa_mainloop_wakeup(pa_mainloop *m) {
> pa_log("pa_write() failed while trying to wake up the mainloop: %s", pa_cstrerror(errno));
> }
>
> -static void clear_wakeup(pa_mainloop *m) {
> - char c[10];
> -
> - pa_assert(m);
> -
> - while (pa_read(m->wakeup_pipe[0], &c, sizeof(c), &m->wakeup_pipe_type) == sizeof(c))
> - ;
> -}
> -
> int pa_mainloop_prepare(pa_mainloop *m, int timeout) {
> pa_assert(m);
> pa_assert(m->state == STATE_PASSIVE);
>
> - clear_wakeup(m);
> scan_dead(m);
>
> if (m->quit)
>
--
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic
