[Intel-gfx] [RFC v2 3/3] drm/i915/pmu: deny perf driver level sampling of i915 PMU

[Peter Zijlstra]

On Wed, Aug 23, 2017 at 11:43:13PM +0000, Rogozhkin, Dmitry V wrote:
> Hi Chris,
> 
> Why we had event->hw->hrtimer in i915 PMU? Was there any particular
> reason? You had some use case which did not work?

Some uncore drivers have a hrtimer to poll the counter to deal with
counter overflow. This is needed when the hardware has 'short' counters.

For instance, the regular uncore stuff has 48 bit counters, so we need a
timer to occasionally read them to fold the delta into our 64bit counter
value.