[Intel-gfx] [PATCH] drm/i915/pmu: "Frequency" is reported as accumulated cycles

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-11-11 10:40:17)
> 
> On 11/11/2019 09:43, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2019-11-11 09:11:03)
> >>
> >> On 09/11/2019 10:53, Chris Wilson wrote:
> >>> We report "frequencies" (actual-frequency, requested-frequency) as the
> >>> number of accumulated cycles so that the average frequency over that
> >>> period may be determined by the user. This means the units we report to
> >>> the user are Mcycles (or just M), not MHz.
> >>>
> >>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >>> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >>> Cc: stable at vger.kernel.org
> >>> ---
> >>>    drivers/gpu/drm/i915/i915_pmu.c | 4 ++--
> >>>    1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> >>> index 4804775644bf..9b02be0ad4e6 100644
> >>> --- a/drivers/gpu/drm/i915/i915_pmu.c
> >>> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> >>> @@ -908,8 +908,8 @@ create_event_attributes(struct i915_pmu *pmu)
> >>>                const char *name;
> >>>                const char *unit;
> >>>        } events[] = {
> >>> -             __event(I915_PMU_ACTUAL_FREQUENCY, "actual-frequency", "MHz"),
> >>> -             __event(I915_PMU_REQUESTED_FREQUENCY, "requested-frequency", "MHz"),
> >>> +             __event(I915_PMU_ACTUAL_FREQUENCY, "actual-frequency", "M"),
> >>> +             __event(I915_PMU_REQUESTED_FREQUENCY, "requested-frequency", "M"),
> >>>                __event(I915_PMU_INTERRUPTS, "interrupts", NULL),
> >>>                __event(I915_PMU_RC6_RESIDENCY, "rc6-residency", "ns"),
> >>>        };
> >>>
> >>
> >> MHz was wrong yes. But is 'M' established or would 'Mcycles' be better?
> > 
> > The only place where "cycles" pops up is in the perf ui, the other
> > events that I thought were similar in nature are unitless. As the
> > 'cycle' itself is not an SI base unit as it is a mere count.
> > 
> > ~o~ I have no idea ~o~
> 
> But if the argument if that 'cycle' is not SI then neither is 'M'. So I 
> think I would prefer 'Mcycles'. Nevertheless, I guess a strange 'M' is 
> better than wrong 'MHz'.

Yeah, I'm really tempted to say we should just remove the M as well but
what a waste of bits!

I think 'M' is understandable from context, whereas MHz was quite
misleading in perf stat :)

Still, if we ever get any feedback, it should be easy to fix :)
-Chris