[Pixman] [ssse3]Optimization for fetch_scanline_x8r8g8b8

[Siarhei Siamashka]

On Monday 30 August 2010 23:31:35 Siarhei Siamashka wrote:
> And Intel Atom does not like software prefetch very much. This reminds me an
> older report:
> http://lists.freedesktop.org/archives/pixman/2010-June/000218.html
> 
> I can try to run a full set of cairo-perf-trace benchmarks to get more
> relevant numbers regarding the effect of software prefetch on Intel Atom.

Looks like this data has been posted already:
http://lists.freedesktop.org/archives/pixman/2010-June/000231.html

Checking a few more things with microbenchmarks shows that the prefetch 
distance of just 64 bytes ahead is way too small. It has to be increased up to 
something like 256-320 to get good memory performance. Apparently software 
prefetch also disables or interferes with the hardware prefetcher on Intel 
Atom, hurting performance a lot. More advanced processors can cope with it.

But increased prefetch distance is less effective (or can even decrease 
performance) when dealing with small images, so it is not always good.

Are there any SSE2 capable x86 processors without hardware prefetch capability? 
Maybe it's really a good idea to remove software prefetch from SSE2 fast path 
code?

-- 
Best regards,
Siarhei Siamashka
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