[Intel-gfx] [CI] drm/i915/pmu: Do not assume fixed hrtimer period

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-06-05 15:02:53)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> As Chris has discovered on his Ivybridge, and later automated test runs
> have confirmed, on most of our platforms hrtimer faced with heavy GPU load
> can occasionally become sufficiently imprecise to affect PMU sampling
> calculations.
> 
> This means we cannot assume sampling frequency is what we asked for, but
> we need to measure the interval ourselves.
> 
> This patch is similar to Chris' original proposal for per-engine counters,
> but instead of introducing a new set to work around the problem with
> frequency sampling, it swaps around the way internal frequency accounting
> is done. Instead of accumulating current frequency and dividing by
> sampling frequency on readout, it accumulates frequency scaled by each
> period.
> 
> v2:
>  * Typo in commit message, comment on period calculation and USER_PER_SEC.
>    (Chris Wilson)

Ironic typo in pointing out the typo?

/me can't tell if it's humour or just an annoying user.
-Chris