[Bug 100913] 6% performance drop in GpuTest v0.7 Volplosion with "remove GLSL IR optimisation loop"

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Fri May 5 02:53:35 UTC 2017


--- Comment #5 from Timothy Arceri <t_arceri at yahoo.com.au> ---
(In reply to Matt Turner from comment #2)
> Looks like this regression could/should have been caught by shader-db:
> LOST:   shaders/closed/gputest/volplosion/7.shader_test FS SIMD16
> Separately, Curro is having an interesting time with this particular shader
> with his new scheduler. Perhaps if that is sorted out, the regression will
> be fixed.

Right. As Ken said there were differences noticed, but it would be pretty
difficult to not see any difference considering the change.

The results from BDW as per the commit message were:


Looking at the output the only real difference I can see is the ordering of the
final nir instructions which seems makes a big diff to the scheduler.

It appears when the vectors are split in nir the instructions seem to be
grouped together as per the execution order of the vectors in the shader, in
contrast the GLSL IR the instructions seem to be order such that they are
grouped slightly more towards executing more instructions on a channel one
after the other. This is probably enough to free up some registers.

I suspect the only thing we can do is wait for Curros new scheduler. We could
revert the change, but that just feels like it hides the problem rather than
fixes it and would be a step backwards IMO.

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