Re: [PATCH v4] drm/vkms: Add support to 1D gamma LUT

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Sat, 24 Jun 2023 18:48:08 -0300
Maira Canal <mairacanal@riseup.net> wrote:

> Hi Arthur,
> 
> Thanks for working on this feature for the VKMS!
> 
> On 6/21/23 16:41, Arthur Grillo wrote:
> > Support a 1D gamma LUT with interpolation for each color channel on the
> > VKMS driver. Add a check for the LUT length by creating
> > vkms_atomic_check().
> > 
> > Tested with:
> > igt@kms_color@gamma
> > igt@kms_color@legacy-gamma
> > igt@kms_color@invalid-gamma-lut-sizes  
> 
> Could you also mention that this will make it possible to run the test 
> igt@kms_plane@pixel-format?
> 
> Also, you mentioned to me that the performance degraded with this new 
> feature, but I wasn't able to see it while running the VKMS CI. I 
> performed a couple of tests and I didn't see any significant performance 
> issue.
> 
> Could you please run a benchmark and share the results with us? This way 
> we can atest that this new feature will not affect significantly the 
> VKMS performance. It would be nice to have a small brief of this 
> benchmark on the commit message as well.
> 
> Attesting that there isn't a performance issue and adding those nits to 
> the commit message, you can add my
> 
> Reviewed-by: Maíra Canal <mairacanal@riseup.net>
> 
> on the next version.

Hi,

perfomance testing is good indeed. As future work, could there be a
document describing how to test VKMS performance?

"I ran IGT@blah 100 times and it took xx seconds before and yy seconds
after" does not really give someone like me an idea of what was
actually measured. For example blending overhead increase could be
completely lost in opaque pixel copying noise if the test case has only
few pixels to blend, e.g. a cursor plane, not to mention the overhead
of launching an IGT test in the first place.

Something that would guide new developers in running meaningful
benchmarks would be nice.

Should e.g. IGT have explicit (VKMS) performance tests that need to be
run manually, since evaluation of the result is not feasible
automatically? Or a benchmark mode in correctness tests that would run
the identical operation N times and measure the time before checking
for correctness?

The correctness verification in IGT tests, if done by image comparison
which they undoubtedly will need to be in the future, may dominate the
CPU run time measurements if included.


Thanks,
pq

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