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Date:   Tue, 4 Apr 2023 18:00:10 +0200
From:   Andi Shyti <andi.shyti@linux.intel.com>
To:     Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc:     Andi Shyti <andi.shyti@linux.intel.com>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org,
        Chris Wilson <chris.p.wilson@linux.intel.com>,
        Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [PATCH v2] drm/i915/gt: Hold a wakeref for the active VM
Message-ID: <ZCxJitP+XtC2/run@ashyti-mobl2.lan>
References: <20230330-hold_wakeref_for_active_vm-v2-1-724d201499c2@intel.com>
 <ZCxEoelnOSpRiy6A@ashyti-mobl2.lan>
 <f193eb7f-19f9-b9a8-7edf-438dafb74da4@linux.intel.com>
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In-Reply-To: <f193eb7f-19f9-b9a8-7edf-438dafb74da4@linux.intel.com>
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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