[Bug 109505] [GEN9+] 2% perf drop in Unigine Heaven, 1% in Valley

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109505

Eero Tamminen <eero.t.tamminen at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |VERIFIED

--- Comment #6 from Eero Tamminen <eero.t.tamminen at intel.com> ---
(In reply to Mark Janes from comment #5)
> Mesa engineers took a look at this, and decided that the performance penalty
> represents the cost of enabling preemption.
>
> Since the performance penalty is slight, the team decided not to address it.

I assume it's the PIPE_CONTROL_RENDER_TARGET_FLUSH when toggling preemption.

Neither Heaven nor Valley use any of the draw types that require disabling
preemption, but they do use instancing.

GfxBench Manhattan tests use in addition to instancing, also Triangle FAN draw
type, but I didn't check how much they alternates those with the other draw
types & non-instancing draws (that can be pre-empted on GEN9). It's anyway
likely that they're slightly impacted also, but happily impact is below daily
variance.


> Benchmarks will not measure the improvements to system responsiveness that
> come from this feature.  Sometimes we need to make the choice that a
> benchmark score is not the most important indicator of our driver's
> performance, even if it is the most visible one.

Yep, most important was bisecting this so that an informed decision can be done
about it.

VERIFIED.

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