Re: [PATCH v2 3/3] drm/i915: Defer declaration of missed-interrupt until the waiter is asleep

Chris Wilson
2017-02-17T11:51:53Z

On Fri, Feb 17, 2017 at 11:43:15AM +0000, Chris Wilson wrote:
> On Fri, Feb 17, 2017 at 01:35:15PM +0200, Mika Kuoppala wrote:
> > Chris Wilson <chris@chris-wilson.co.uk> writes:
> >
> > > If the waiter was currently running, assume it hasn't had a chance
> > > to process the pending interupt (e.g, low priority task on a loaded
> > > system) and wait until it sleeps before declaring a missed interrupt.
> > >
> > > References: https://bugs.freedesktop.org/show_bug.cgi?id=99816
> > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> > > ---
> > > drivers/gpu/drm/i915/intel_breadcrumbs.c | 9 +++++++++
> > > 1 file changed, 9 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> > > index 4395b177493e..2ad29fb77b2d 100644
> > > --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
> > > +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> > > @@ -45,6 +45,15 @@ static void intel_breadcrumbs_hangcheck(unsigned long data)
> > > return;
> > > }
> > >
> > > + /* If the waiter was currently running, assume it hasn't had a chance
> > > + * to process the pending interupt (e.g, low priority task on a loaded
> > > + * system) and wait until it sleeps before declaring a missed interrupt.
> > > + */
> > > + if (!intel_engine_wakeup(engine)) {
> >
> > But this will happen if there is waiter running, or that there is
> > no waiter at all.
> >
> > Don't we need to exclude the latter?
>
> We already exclude the latter by cancelling this timer above.

Ah, it's not as clear in the current tree as it will be! Here is the
b->irq_enabled check that is equivalent to checking for a waiter.
When there are no more waiters, we set irq_enabled to false and so
cancel the timer.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre