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

[Tvrtko Ursulin]

On 31/03/2023 15:16, 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.
>
> v2: added explanation to __queue_and_release_pm
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> [ahajda: removed not-yet-upstremed wakeref tracking bits]
> Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> ---
> Changes in v2:
> - Link to v1: https://lore.kernel.org/r/20230330-hold_wakeref_for_active_vm-v1-1-baca712692f6@xxxxxxxxx
> ---
>   drivers/gpu/drm/i915/gt/intel_context.h   | 15 +++++++++++----
>   drivers/gpu/drm/i915/gt/intel_engine_pm.c |  9 +++++++++
>   2 files changed, 20 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);
>   }
>   
>   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);
> +
>   	/*
>   	 * We have to serialise all potential retirement paths with our
>   	 * submission, as we don't want to underflow either the

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko