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

  From: Chris Wilson <chris@chris-wilson.co.uk>

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@chris-wilson.co.uk>
[ahajda: removed not-yet-upstremed wakeref tracking bits]
Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
Changes in v2:
- Link to v1: https://lore.kernel.org/r/20230330-hold_wakeref_for_active_vm-v1-1-baca712692f6@intel.com
---
 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(-)


---
base-commit: 3385d6482cd60f2a0bbb0fa97b70ae7dbba4f95c
change-id: 20230330-hold_wakeref_for_active_vm-7f013a449ef3

Best regards,
  

On 31/03/2023 15:16, Andrzej Hajda wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> 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@chris-wilson.co.uk>
> [ahajda: removed not-yet-upstremed wakeref tracking bits]
> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
> ---
> Changes in v2:
> - Link to v1: https://lore.kernel.org/r/20230330-hold_wakeref_for_active_vm-v1-1-baca712692f6@intel.com
> ---
>   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@intel.com>

Regards,

Tvrtko
  

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"?

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>
  

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>
  

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
  

On 04/04/2023 17:00, Andi Shyti wrote:
> 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

I missed this one.

> 	ce->ops->exit(ce);
> 	intel_gt_pm_put_async(ce->vm->gt);
> 
> Don't we need to hold the pm until exiting?

I think it doesn't matter. The problematic edge case this is fixing is 
when ce->engine->gt is different from ce->vm->gt but at this point if it 
is safe to release one it must be safe to release the other too.

Regards,

Tvrtko


> 
>>>>    }
>>>>    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
  

Hi,

On Fri, Mar 31, 2023 at 04:16:36PM +0200, Andrzej Hajda wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> 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@chris-wilson.co.uk>
> [ahajda: removed not-yet-upstremed wakeref tracking bits]
> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>

Thank you Tvrtko and Chris for answering my questions,

Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> 

Andi
  

On 31.03.2023 16:16, Andrzej Hajda wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> 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@chris-wilson.co.uk>
> [ahajda: removed not-yet-upstremed wakeref tracking bits]
> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>


Queued.

Regards
Andrzej