Re: [PATCH 7/8] drm/i915/pmu: Wire up engine busy stats to PMU

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 25/09/2017 18:48, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2017-09-25 16:15:42)
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> We can use engine busy stats instead of the MMIO sampling timer
>> for better efficiency.
>>
>> As minimum this saves period * num_engines / sec mmio reads,
>> and in a better case, when only engine busy samplers are active,
>> it enables us to not kick off the sampling timer at all.
> 
> Or you could inspect port_isset(execlists.port).
> You can avoid the mmio for this case also by just using HWSP. It's just
> that I never enabled busy tracking in isolation, so I always ended up
> using the mmio.

This would be for execlists only. I could change the main patch to do 
this, you think it is worth it?

> Stronger argument is that this method give more precise timing than
> stochastic sampling.
> 
>>
>> v2: Rebase.
>> v3:
>>   * Rebase, comments.
>>   * Leave engine busyness controls out of workers.
>> v4: Checkpatch cleanup.
>> v5: Added comment to pmu_needs_timer change.
>> v6:
>>   * Rebase.
>>   * Fix style of some comments. (Chris Wilson)
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> With a better explanation of why this is preferred,
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Thanks,

Tvrtko

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