[FFmpeg-devel] swscale/unscaled : Remove MMXext version of shufflebyte2103 and uyvyto422

Michael Niedermayer michael at niedermayer.cc
Mon Apr 9 04:00:17 EEST 2018

On Sun, Apr 08, 2018 at 03:33:17PM +0200, Martin Vignali wrote:
> Hello,
> Patchs in attach remove mmxext version of shufflebytes2103 and uyvyto422
> Checkasm test show that mmxext version is slower than MMX version
> Also disable MMXext for "internal" func : extract_even2
> (only use by uyvyto422)

are you testing these functions with real image data in a real image
processing pipeline ?

synthetic tests would likely not give correct results with non temporal
in a real processing pipeline the output image will generally not fit in
the L1 cache and will generally not be reused before other things overwrote
the cache. So it should be better not to waste cache for it in the first
But a synthetic test which just repeatly filters a short line will
behave very differently.
Its thus expected that mmx2 performs poorly here in such a synthetic test
but that doesnt say anything about how it performs in a real use case


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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