[Intel-gfx] [RFC] drm/i915: Reduce locking in command submission

[Tvrtko Ursulin]

On 12/15/2014 01:06 PM, Daniel Vetter wrote:
> On Thu, Dec 11, 2014 at 03:41:34PM +0000, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>
>> Eliminate six needless spin lock/unlock pairs when writing ELSP.
>>
>> RFC for now with some #define copy and paste.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> Cc: Dave Gordon <david.s.gordon at intel.com>
>
> Yeah makes sense. I'm on the fence whether we should do an all-uppercase
> conversion of the raw mmio macros, would be a nothc more consistent. And
> some perf data for this patch would be good, too.

With regards to perf data, Ben Widawsky was kind enough to give this 
patch a spin on his perf test bed (CHV), on a range of OGL benchmarks.

Apparently only two results have "confidence t-score" > 95% (statistics 
is not my area), bench_OglBatch4 and bench_OglDeferred which show 0.51% 
and 0.73% gains respectively.

Looking just on the basis of those two, I'd say the patch is worth 
cleaning up since it is a good gain for such a simple change.

Other results show anything from 4.29% slowdown (!*) 
(bench_OglTexFilterAniso) to a 7.08% gain (bench_OglMultithreaded).

Average across all benchmarks is a 0.38% gain.

Thoughts?

Regards,

Tvrtko

* I can't really understand regressions for some tests?!