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

[Chris Wilson]

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.
-Chris