On Mon, 2014-07-28 at 11:08 +0200, Peter Zijlstra wrote:
> On Sun, Jul 27, 2014 at 10:18:41PM -0700, Davidlohr Bueso wrote:
> > +static bool mutex_optimistic_spin(struct mutex *lock,
> > + struct ww_acquire_ctx *ww_ctx, const bool
> > use_ww_ctx)
> > +{
>
>
> > + /*
> > + * If we fell out of the spin path because of need_resched(),
> > + * reschedule now, before we try-lock the mutex. This avoids getting
> > + * scheduled out right after we obtained the mutex.
> > + */
> > + if (need_resched())
> > + schedule_preempt_disabled();
> > +
> > + return false;
> > +}
>
>
> > + if (mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) {
> > + /* got it, yay! */
> > + preempt_enable();
> > + return 0;
> > }
> > +
> > /*
> > * If we fell out of the spin path because of need_resched(),
> > * reschedule now, before we try-lock the mutex. This avoids getting
> > @@ -475,7 +512,7 @@ slowpath:
> > */
> > if (need_resched())
> > schedule_preempt_disabled();
> > +
> > spin_lock_mutex(&lock->wait_lock, flags);
>
> We now have two if (need_resched) schedule_preempt_disable() instances,
> was that on purpose?
I think we can delete the extra check in mutex_optimistic_spin(). It is
sufficient to have it here and it also covers the case where the task
need_resched() without attempting to spin.
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