Re: [PATCH v2] drm/i915/gt: Hold a wakeref for the active VM

[Tvrtko Ursulin]

On 04/04/2023 16:39, Andi Shyti wrote:
> Hi Andrzej,
>
> > diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
> > index 0a8d553da3f439..48f888c3da083b 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_context.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_context.h
> > @@ -14,6 +14,7 @@
> >   #include "i915_drv.h"
> >   #include "intel_context_types.h"
> >   #include "intel_engine_types.h"
> > +#include "intel_gt_pm.h"
> >   #include "intel_ring_types.h"
> >   #include "intel_timeline_types.h"
> >   #include "i915_trace.h"
> > @@ -207,8 +208,11 @@ void intel_context_exit_engine(struct intel_context *ce);
> >   static inline void intel_context_enter(struct intel_context *ce)
> >   {
> >   	lockdep_assert_held(&ce->timeline->mutex);
> > -	if (!ce->active_count++)
> > -		ce->ops->enter(ce);
> > +	if (ce->active_count++)
> > +		return;
> > +
> > +	ce->ops->enter(ce);
> > +	intel_gt_pm_get(ce->vm->gt);
> >   }
> >   
> >   static inline void intel_context_mark_active(struct intel_context *ce)
> > @@ -222,8 +226,11 @@ static inline void intel_context_exit(struct intel_context *ce)
> >   {
> >   	lockdep_assert_held(&ce->timeline->mutex);
> >   	GEM_BUG_ON(!ce->active_count);
> > -	if (!--ce->active_count)
> > -		ce->ops->exit(ce);
> > +	if (--ce->active_count)
> > +		return;
> > +
> > +	intel_gt_pm_put_async(ce->vm->gt);
> > +	ce->ops->exit(ce);
>
> shouldn't these two be swapped?
>
> >   }
> >   
> >   static inline struct intel_context *intel_context_get(struct intel_context *ce)
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> > index e971b153fda976..ee531a5c142c77 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> > @@ -114,6 +114,15 @@ __queue_and_release_pm(struct i915_request *rq,
> >   
> >   	ENGINE_TRACE(engine, "parking\n");
> >   
> > +	/*
> > +	 * Open coded one half of intel_context_enter, which we have to omit
> > +	 * here (see the large comment below) and because the other part must
> > +	 * not be called due constructing directly with __i915_request_create
> > +	 * which increments active count via intel_context_mark_active.
> > +	 */
> > +	GEM_BUG_ON(rq->context->active_count != 1);
> > +	__intel_gt_pm_get(engine->gt);
>
> where is it's brother "put"?

It's in request retire via intel_context_exit. Ie. request construction 
is special here, while retirement is standard.

Regards,

Tvrtko

> Thanks,
> Andi
>
> > +
> >   	/*
> >   	 * We have to serialise all potential retirement paths with our
> >   	 * submission, as we don't want to underflow either the
> >
> > ---
> > base-commit: 3385d6482cd60f2a0bbb0fa97b70ae7dbba4f95c
> > change-id: 20230330-hold_wakeref_for_active_vm-7f013a449ef3
> >
> > Best regards,
> > --
> > Andrzej Hajda <andrzej.hajda@xxxxxxxxx>