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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

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@intel.com>