[Bug 107410] [SKL] Up to 20% performance regression in GpuTest Triangle, due to 2x higher CPU power usage

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107410

--- Comment #11 from Eero Tamminen <eero.t.tamminen at intel.com> ---
(In reply to Eero Tamminen from comment #8)
> (In reply to Srinivas Pandruvada from comment #6)
> > If this fixes, try the attached patch.
> 
> I'm running the full set of benchmarks with this, so it takes a while.
> I'll report  results tomorrow.

Yes, the attached patch fixed all the regressions.


(In reply to Eero Tamminen from comment #0)
> There were no improvements in any 3D benchmarks from this, but I noticed
> small increase in SIMD CPU copy and large increase in SIMD CPU read
> performance.  However, that was only on SKL GT2, not GT4e, so it may be
> unrelated.

The fix patch regressed Unigine Valley slightly.  On closer look Valley had
actually increased with original change (by 1.0-1.5%), but only on SKL GT2. 
I.e. there was actually one platform with one 3D benchmark where the initial
change improved perf slightly (without any noticeable increase in CPU power
usage).

-> I assume the SKL GT2 CPU read performance (25%) improvement was also due to
original change, but the improvement is very much a corner case [1].

[1] SKL-i5 6600K has 4 real cores.  CPU read (performance with 64MB block
improved with the original change *only* in following cases:
- SSE2   with 4 threads
- SSE4.1 with 6 threads
- AVX1/2 with 6 threads

It didn't improve when the number of running SIMD threads was smaller or larger
that those.

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