[Mesa-dev] i965: disable_throttling

[Eero Tamminen]

Hi,

On 12.06.2017 06:58, Marathe, Yogesh wrote:
>> -----Original Message-----
>> On 09.06.2017 09:21, Marathe, Yogesh wrote:
>>> I’m looking forward to set this brw->disable_throttling to true, I’m
>>> actually observing adverse effect on performance benchmarks after I
>>> force set that to true. What’s the expectation from disable_throttling
>>> here?
>>
>> By default Mesa throttles its buffer swaps so that compositor is able to easier
>> insert its own batches to better place in GPU batch queue.
>>
>> If throttling is disabled, compositor needs to discard more frames as obsolete,
>> because benchmark is running too many frames forward of it.
>>
>> Normally having no throttling means that:
>> * composited performance looks worse to the user, because only some of the
>> rendered frames end up on screen
>> * benchmark runs faster because compositor composes less frames, i.e.
>> takes less of the system bandwidth
>>
>
> Thanks Eero. Essentially, you are saying having disable_trottling=true is
> actually _not_ beneficial from compositor's perspective where GPU is not
> matching speeds with that of benchmark. I will leave it to default then.

If you're doing performance comparisons against drivers which don't do 
this kind of throttling (and where system doesn't support GPU 
pre-empting / batch prioritization), it should be fairly easy to notice. 
  Benchmark doesn't look even nearly as smooth as it should be, 
according to the FPS reported by the benchmark.

Then it does make sense to disable throttling from Mesa, to make 
comparison against the other driver more apples-to-apples.


	- Eero

>>  > BTW, this is on android.
>>
>> On TDP constrained machines, power management can do funky things.  When
>> in doubt, use fixed GPU & CPU speeds are re-test.
>>
>
> Alright.