[Intel-gfx] [PATCH] drm/i915/pmu: Report frequency as zero while GPU is sleeping

[Chris Wilson]

Quoting Chris Wilson (2019-11-28 16:19:49)
> Quoting Tvrtko Ursulin (2019-11-28 16:10:51)
> > From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > 
> > We used to report the minimum possible frequency as both requested and
> > active while GPU was in sleep state. This was a consequence of sampling
> > the value from the "current frequency" field in our software tracking.
> > 
> > This was strictly speaking wrong, but given that until recently the
> > current frequency in sleeping state used to be equal to minimum, it did
> > not stand out sufficiently to be noticed as such.
> > 
> > After some recent changes have made the current frequency be reported
> > as last active before GPU went to sleep, meaning both requested and active
> > frequencies could end up being reported at their maximum values for the
> > duration of the GPU idle state, it became much more obvious that this does
> > not make sense.
> > 
> > To fix this we will now sample the frequency counters only when the GPU is
> > awake. As a consequence reported frequencies could be reported as below
> > the GPU reported minimum but that should be much less confusing that the
> > current situation.
> > 
> > Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Hmm. 0/0 while off, that will be a bit of a shock.

There is a consistency question of whether we should do the same through
the [second class ;] sysfs/ interface.
-Chris