[Intel-gfx] [PATCH igt 1/3] igt/perf_pmu: Idle the GPU before starting to measure busyness

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-11-22 20:12:54)
> 
> On 22/11/2017 18:05, Chris Wilson wrote:
> > Make sure the HW is idle before we start sampling the GPU for busyness.
> > If we do not rest for long enough between tests, we may carry the
> > sampling over.
> 
> Hm.. not sure about this one. New PMU client is supposed to start with a 
> counter relative to the current value at counter enable. How did you 
> come to this being a problem?

I was just staring at the legacy submission inaccuracy, thinking it was
due to sampling earlier state and the knee-jerk reaction is to put
quiescent gpu between failed subtests. (Which is due to not clearing the
prev across parked :) I haven't tested without this part, but with the two
parts combined, perf_pmu on byt has been stable (passing).
-Chris