[cairo] pixman NEON problems

[Siarhei Siamashka]

On Wednesday 08 July 2009, Yogish Kulkarni wrote:
> Have anybody tried pixman with neon optimisations on OMAP3 platform ?

Yes, welcome aboard :)

> While running render bench, strange horizontal lines are coming on
> screen. I used latest version from pixman repo.

This is a known issue (currently under investigation), and actually may be
triggered by either the kernel or pixman, or both of them:
http://lists.cairographics.org/archives/cairo/2009-July/017548.html

Kernel is definitely a part of the problem. Just because using old pixman
version without any ARM assembly optimizations but having NEON optimized
memcpy in the system also results in similar visual glitches when scrolling
windows. After applying VFP state corruption fixes to the kernel, these
problems disappear.

Some of the NEON related pixman problems are also summarized here:
http://lists.cairographics.org/archives/cairo/2009-July/017555.html

Everything is expected to change for the better very soon.

> Are there any performance improvement figures for neon optimised
> pixman ?

Doing reliable/reproducible benchmarking and finetuning NEON optimizations
up to their best is something that needs to be also done, once the code is
correct.

If you have some good benchmarks or usecases which need to be improved, this
information could be interesting.

-- 
Best regards,
Siarhei Siamashka