[Intel-gfx] [PATCH] drm/i915: Special handling for bonded requests

[Tvrtko Ursulin]

On 28/05/2020 10:57, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2020-05-27 09:53:22)
>> +static void
>> +mark_bonded_pair(struct i915_request *rq, struct i915_request *signal)
>> +{
>> +       /*
>> +        * Give (temporary) special meaning to a pair requests with requested
>> +        * aligned start along the video engines.
>> +        *
>> +        * They should be non-preemptable and have all ELSP ports to themselves
>> +        * to avoid any deadlocks caused by inversions.
>> +        *
>> +        * Gen11+
>> +        */
>> +       if (INTEL_GEN(rq->i915) < 11 ||
>> +           rq->engine->class != VIDEO_DECODE_CLASS ||
>> +           rq->engine->class != signal->engine->class)
>> +               return;
>> +
>> +       set_bit(I915_FENCE_FLAG_NOPREEMPT, &rq->fence.flags);
>> +       set_bit(I915_FENCE_FLAG_NOPREEMPT, &signal->fence.flags);
>> +
>> +       intel_context_set_single_submission(rq->context);
>> +       intel_context_set_single_submission(signal->context);
> 
> The thought that just popped into my head:
> 
> This can be after signal is already submitted into ELSP[1].

Yep I knew that but thought it would still work.

Master in vcs0 port1, slave in vcs1 port0 or queued.

If queued that means at worst case another bonded pair is running on 
same engines, so they should be able to complete.

If slave submitted to vcs1 port0 then it will stay there until whatever 
is in vcs0 port0 finishes and lets master in.

Do you see a possibility for things to go bad?

Regards,

Tvrtko