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

[Tvrtko Ursulin]

On 28/11/2019 16:22, Chris Wilson wrote:
> 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.

I am not sure cur_freq even belongs in sysfs. But IGT/i915_pm_rps seems 
to be depending on the current semantics.

Act_freq on the other hand is always reading the hw register. So should 
probably stay like that. Since it is in sysfs so ABI.

Where this leaves the PMU I don't know.

Regards,

Tvrtko