[cairo] scaling performance test of cairo library

[Andrea Canciani]

On Tue, Feb 8, 2011 at 2:23 PM, Siarhei Siamashka
<siarhei.siamashka at gmail.com> wrote:
> On Tuesday 08 February 2011 06:52:02 cooolheater wrote:
>> Hi,
>> I'm developer of mobile browser using webkit with cairo library.
>> Recently, I did performance comparing test between cairo 1.10.02 and skia
>> library.
>
> Thanks for your benchmarking data. What kind of hardware have you used for
> running this benchmark? And because you are using cairo image backend, the
> version of pixman library is also important because it is actually doing all
> the scaling work.
>
>> The performance of compstion and rotating seems similar,
>
> Performance of rotation in pixman should be horrible right now, don't know if
> I should be happy to know that skia seems to be just as bad :)
>
> What kind of rotation are you are interested in? The following patches should
> help with some types of rotation, and can be extended if needed:
> http://lists.freedesktop.org/archives/pixman/2011-February/000970.html
>
>> but scaling performance of cairo library seems quite low.
>
> On non-SIMD capable processors, cairo/pixman should have bilinear scaling
> performing roughly as fast as the other good implementations, so I assume that
> some kind of SIMD is supported on your target system.
>
> A problem with bilinear scaling performance in pixman is that it does not have
> SIMD optimizations yet. That's something that I'm currently looking into, at
> least for ARM NEON.
>
> Also your benchmarks show that the overhead before reaching actual scaling code
> is much lower with skia as can be seen for very small sizes of images. It's
> still questionable how much such overhead affects real use cases, but I'm
> expressing concern here from time to time whenever I see the patches which seem
> to be increasing this overhead in pixman more than necessary.

Profile data would be needed to confirm this, but my guess is that most of the
overhead is actually in cairo.

>
> The only surprising thing in your data is that skia seems to have really poor
> performance for nearest scaling, but probably they just primarily focused on
> making bilinear scaling fast.

The cairo bilinear/nearest ratio looks more surprising to me.
What is the reason for a 40x slowdown?
I didn't expect the generic path to be so much slower than fast paths.

Andrea