[Intel-gfx] [PATCH i-g-t v4] tests/perf_pmu: Avoid RT thread for accuracy test

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-04-04 10:51:52)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Realtime scheduling interferes with execlists submission (tasklet) so try
> to simplify the PWM loop in a few ways:
> 
>  * Drop RT.
>  * Longer batches for smaller systematic error.
>  * More truthful test duration calculation.
>  * Less clock queries.
>  * No self-adjust - instead just report the achieved cycle and let the
>    parent check against it.
>  * Report absolute cycle error.
> 
> v2:
>  * Bring back self-adjust. (Chris Wilson)
>    (But slightly fixed version with no overflow.)
> 
> v3:
>  * Log average and mean calibration for each pass.
> 
> v4:
>  * Eliminate development leftovers.
>  * Fix variance logging.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

From a pragmatic point of view, there's no point waiting for me to be
happy with the convergence if CI is, and the variance will definitely be
interesting (although you could have used igt_mean to compute the
iterative variance), so

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