[Bug 108598] [GEN9] 20% perf drop in windowed/composited GpuTest Triangle

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108598

--- Comment #4 from Eero Tamminen <eero.t.tamminen at intel.com> ---
(In reply to Chris Wilson from comment #1)
> That metric may not include the frequency of screen updates, which is the
> likely change here in the composited case. My suspicion is that we interject
> more work from the xserver resulting in more frames being blitted from
> individual batches as opposed to several frames being amalgamated into a
> single batch. Just a hunch.

Triangle test FPS is *very* high (it does just fast clear and draws
half window sized triangle with trivial shader), whereas Compiz updates
are limited to monitor frequency.

Looking at the collected data:

* Compiz updates at 60Hz, that didn't change.

* GpuTest glXBufferSwap timing distribution changed so that:
  - slowest frames are now 7x slower,
  - fastest frames are 10% faster,
  - median frames are 1-2% slower,
  - which results in average FPS being ~20% slower.

Maybe kernel reacts now worse to Mesa frame throttling behavior?

(Controlled by Mesa "disable_throttling" env var.)


If you're interested, I can send you scripts to track & visualize
individual buffer swap timings and GPU & CPU speeds.

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