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

[Mika Kuoppala]

Chris Wilson <chris at chris-wilson.co.uk> writes:

> 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.

If there will be more users, then we can consider
disable|enable_reschedule_timer or similar.

Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

> -Chris