[Intel-gfx] [PATCH] drm/i915/pmu: Do not report 100% RC6 if not supported

[Tvrtko Ursulin]

On 06/04/2021 12:19, Andi Shyti wrote:
> Hi Tvrtko,
> 
>> We use GT parked status to estimate RC6 while not in use, however if RC6
>> is not supported to start with that does not work very well and produces a
>> false 100% RC6 readout.
>>
>> Fix by not advancing the estimated RC6 counter when feature is not
>> supported.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> Fixes: 1fe699e30113 ("drm/i915/pmu: Fix sleep under atomic in RC6 readout")
>> Reported-by: Eero T Tamminen <eero.t.tamminen at intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_pmu.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
>> index 41651ac255fa..02fe0d22c470 100644
>> --- a/drivers/gpu/drm/i915/i915_pmu.c
>> +++ b/drivers/gpu/drm/i915/i915_pmu.c
>> @@ -191,7 +191,10 @@ static u64 get_rc6(struct intel_gt *gt)
>>   		 * on top of the last known real value, as the approximated RC6
>>   		 * counter value.
>>   		 */
>> -		val = ktime_since_raw(pmu->sleep_last);
>> +		if (gt->rc6.supported)
>> +			val = ktime_since_raw(pmu->sleep_last);
>> +		else
>> +			val = 0;
> 
> if rc6 is not supported, why are we here?

There is another flavour of this patch which indeed prevents us from 
getting here if rc6 is not enabled. (By not exposing the counter if not 
supported.)

> 
> Did you mean rc6.enabled ?

Yeah, I did not see that one initially at all! But it doesn't matter 
since this patch is not going in anyway.

Regards,

Tvrtko