A small analysis of vector composition results on different architectures

[Boudewijn Rempt]

On Sun, 4 Nov 2012, Dmitry Kazakov wrote:

> Hi!
> 
> First, thanks everyone who helped me with running the composition benchmark on their machines! Now I have some
> important information about what we should do next with these optimizations!
> 
> In the first attached document you can find a table, comparing the results on various architectures.
> 
> Here are conclusions I came to:
> 
> 1) On some architectures, e.g. non-Intel, the usage of Vc may degrade the performance, so Krita should have some
> automatic benchmarking capabilities (in settings dialog, for example), which would select the best available
> implementation of the composite op. Such benchmark might be executed on the first run of Krita and its result
> might be written to a Krita config file.
> 
> 2) Some old processors (Nehalem, Merom) have some problems when one of the pixels (src or dst) have alpha
> channel set to 255. I can't explain right now why this happens. Probably, there is some branch misprediction...
> The rest of the cases on these CPUs are handled properly.
> 
> So in general, I  think these two problems should be solved and after that the branch can be merged into master.
>

Very cool work!

Boudewijn