[Intel-gfx] [PATCH 6/9] drm/i915/selftests: Force bonded submission to overlap

[Tvrtko Ursulin]

On 20/11/2019 12:59, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2019-11-20 12:55:42)
>>
>> On 20/11/2019 09:32, Chris Wilson wrote:
>>> Bonded request submission is designed to allow requests to execute in
>>> parallel as laid out by the user. If the master request is already
>>> finished before its bonded pair is submitted, the pair were not destined
>>> to run in parallel and we lose the information about the master engine
>>> to dictate selection of the secondary. If the second request was
>>> required to be run on a particular engine in a virtual set, that should
>>> have been specified, rather than left to the whims of a random
>>> unconnected requests!
>>>
>>> In the selftest, I made the mistake of not ensuring the master would
>>> overlap with its bonded pairs, meaning that it could indeed complete
>>> before we submitted the bonds. Those bonds were then free to select any
>>> available engine in their virtual set, and not the one expected by the
>>> test.
>>
>> There is a submit await which ensures master is not runnable before
>> bonded pairs are submitted. Why was that not enough? Are the sporadic
>> test failures?
> 
> One test is using the submit_await, the other does not. It takes the
> background retire worker to run as we are submitting the secondaries...
> But I have not noticed this failure before hooking up retirement to
> process_csb. However, the issue is definitely present in the current
> test.

So what happens? Is this another issue limited to selftests? Because I 
don't see that uAPI itself can't be used in this way.

Regards,

Tvrtko