[Intel-gfx] [PATCH 2/8] drm/i915/selftests: Prevent the timeslice expiring during suppression tests

[Chris Wilson]

Quoting Mika Kuoppala (2019-08-12 10:39:01)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > When testing whether we prevent suppressing preemption, it helps to
> > avoid a time slice expiring prematurely.
> >
> 
> I did look the test and it does call schedule on it's own.
> 
> So what we want to do is to postpone the defacto schedule tick
> provided by driver not to mess our own schedule? (which we
> use to check that no preemption does occur with equal
> priorities?)

The test is trying to look at our mechanics to ensure that we don't
cause preemptions where we simply put back the same request. As such, we
have a marker in the preemption code that we are trying to avoid, and
must control the scheduling to exclude all other events than the one we
are injecting.

The timeslice could expire and reverse A,B (to B,A) such that our
promotion of A does (correctly) cause a preemption that we expect never
to need.
-Chris