Re: [FFmpeg-devel] [PATCH v2 1/2] avfilter/vf_blackdetect: add AVX2 SIMD version

[Kieran Kunhya via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

On Fri, Jul 18, 2025 at 1:41 PM Kacper Michajlow <kasper93@gmail.com> wrote:
>
> On Fri, 18 Jul 2025 at 14:14, Kieran Kunhya via ffmpeg-devel
> <ffmpeg-devel@ffmpeg.org> wrote:
> >
> > > blackdetect8_c:                                        820.8 ( 1.00x)
> > > blackdetect8_avx2:                                     219.2 ( 3.74x)
> > > blackdetect16_c:                                       372.8 ( 1.00x)
> > > blackdetect16_avx2:                                    201.4 ( 1.85x)
> > >
> > > Again, sorry for being pedantic here, but it gives the wrong
> > > impression especially if you look at this from outside.
> >
> > Also misleading as far as I understand because GCC doesn't have
> > runtime detection like FFmpeg.
>
> Speak of... actually GCC does have runtime detection. All you have to
> do is mark the function with `target_clones` with requested
> architectures and it will dispatch automatically during runtime the
> best function to use.
>
> See for more information:
> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-target_005fclones-function-attribute

It's not as sophisticated as our runtime detection (e.g avx512 vs
avx512icl which we support).
Comparing C vs autovectorised code that works only on some platforms
with forced compilation settings is also unfair.

Kieran
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