On Wed, Aug 05, 2020 at 06:37:45PM +0200, Paolo Bonzini wrote:
> On 05/08/20 12:00, Stefan Hajnoczi wrote:
> > +
> > + /*
> > + * 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 (use_notify_me) {
> > + atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2);
> > + /*
> > + * Write ctx->notify_me before reading ctx->notified. Pairs
> > with
> > + * smp_mb in aio_notify().
> > + */
> > + smp_mb();
> > +
> > + /* Don't block if aio_notify() was called */
> > + if (atomic_read(&ctx->notified)) {
> > + timeout = 0;
> > + }
>
> Aha, this is the trick: "timeout = 0" also applies if a timer was moved
> early. In this case you uselessly keep notify_me set for a bit, but
> it's okay. Nice!
>
> The code can be simplified a bit more, since the use_notify_me variable
> is just "timeout":Good point. I'll send another revision. Stefan
signature.asc
Description: PGP signature
