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

Andi Shyti
2023-04-04T16:00:52Z

Hi Tvrtko,

> > > 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?

maybe I wasn't clear here... shouldn't it be

ce->ops->exit(ce);
intel_gt_pm_put_async(ce->vm->gt);

Don't we need to hold the pm until exiting?

> > > }
> > > 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.

Thank you!
Andi