[Intel-gfx] [PATCH v2] drm/i915/pmu: Report frequency as zero while GPU is sleeping

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-11-29 10:54:36)
> 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.
> 
> v2:
>  * Split out early exit conditions for readability. (Chris)
> 

Closes: https://gitlab.freedesktop.org/drm/intel/issues/675
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris