Re: [PATCH v2 1/1] psi: stop relying on timer_pending for poll_work rescheduling

[Peter Zijlstra]

On Thu, Jul 01, 2021 at 09:09:25AM -0700, Suren Baghdasaryan wrote:
> On Thu, Jul 1, 2021 at 1:59 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Wed, Jun 30, 2021 at 01:51:51PM -0700, Suren Baghdasaryan wrote:
> > > +     /* cmpxchg should be called even when !force to set poll_scheduled */
> > > +     if (atomic_cmpxchg(&group->poll_scheduled, 0, 1) && !force)
> > >               return;
> >
> > Why is that a cmpxchg() ?
> 
> We want to set poll_scheduled and proceed with rescheduling the timer
> unless it's already scheduled, so cmpxchg helps us to make that
> decision atomically. Or did I misunderstand your question?

What's wrong with: atomic_xchg(&group->poll_scheduled, 1) ?