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

[Rodrigo Vivi]

On Thu, Mar 30, 2023 at 04:35:39PM +0200, Andrzej Hajda wrote:
> From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> 
> There may be a disconnect between the GT used by the engine and the GT
> used for the VM, requiring us to hold a wakeref on both while the GPU is
> active with this request.
> 
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> [ahajda: removed not-yet-upstremed wakeref tracking bits]
> Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> ---
>  drivers/gpu/drm/i915/gt/intel_context.h   | 15 +++++++++++----
>  drivers/gpu/drm/i915/gt/intel_engine_pm.c |  3 +++
>  2 files changed, 14 insertions(+), 4 deletions(-)
> 
> 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);

so far so good. this all matches the commit msg and seems a good move.


>  }
>  
>  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..ac0566c5e99e17 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> @@ -114,6 +114,9 @@ __queue_and_release_pm(struct i915_request *rq,
>  
>  	ENGINE_TRACE(engine, "parking\n");
>  
> +	GEM_BUG_ON(rq->context->active_count != 1);

why do you need this here? should it be a separated patch with
separated explanation?


> +	__intel_gt_pm_get(engine->gt);

why? I mean, why the get in the release pm?
and where's the put for this get?
should it be a separated patch as well?

> +
>  	/*
>  	 * 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>