On Tue, Aug 04, 2020 at 06:53:09PM +0200, Paolo Bonzini wrote:
> On 04/08/20 12:29, Stefan Hajnoczi wrote:
> > On Tue, Aug 04, 2020 at 06:28:04AM +0100, Stefan Hajnoczi wrote:
> >> @@ -597,15 +574,38 @@ bool aio_poll(AioContext *ctx, bool blocking)
> >> * system call---a single round of run_poll_handlers_once suffices.
> >> */
> >> if (timeout || ctx->fdmon_ops->need_wait(ctx)) {
> >> + /*
> >> + * aio_notify can avoid the expensive event_notifier_set if
> >> + * everything (file descriptors, bottom halves, timers) will
> >> + * be re-evaluated before the next blocking poll(). This is
> >> + * already true when aio_poll is called with blocking == false;
> >> + * if blocking == true, it is only true after poll() returns,
> >> + * so disable the optimization now.
> >> + */
> >> + if (timeout) {
> >> + atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2);
> >> + /*
> >> + * Write ctx->notify_me before computing the timeout
> >> + * (reading bottom half flags, etc.). Pairs with
> >> + * smp_mb in aio_notify().
> >> + */
> >> + smp_mb();
> >> +
> >> + /* Check again in case a shorter timer was added */
> >> + timeout = qemu_soonest_timeout(timeout,
> >> aio_compute_timeout(ctx));
> >> + }
> >> +
> >> ret = ctx->fdmon_ops->wait(ctx, &ready_list, timeout);
> >> - }
> >>
> >> - if (blocking) {
> >> - /* Finish the poll before clearing the flag. */
> >> - atomic_store_release(&ctx->notify_me,
> >> atomic_read(&ctx->notify_me) - 2);
> >> - aio_notify_accept(ctx);
> >> + if (timeout) {
> >> + /* Finish the poll before clearing the flag. */
> >> + atomic_store_release(&ctx->notify_me,
> >> + atomic_read(&ctx->notify_me) - 2);
> >> + }
> >> }
> >
> > Hi Paolo,
> > We can avoid calling aio_compute_timeout() like this, what do you think?
>
> I don't understand :) except I guess you mean we can avoid the second
> call. Can you post either a complete patch with this squashed, or a 4th
> patch (whatever you think is best)?Sure, I'll post a new revision of this series. Stefan
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