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

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-06-05 16:06:57)
> 
> On 05/06/2018 15:20, Chris Wilson wrote:
> > 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.
> 
> More typos? Where? Don't see anything and neither does my spellchecker! :)

s/USER_PER_SEC/USEC_PER_SEC/
-Chris