[FFmpeg-devel] [PATCH 1/2] libavutil/cpu: Adds av_cpu_has_fast_gather to detect cpus with avx fast gather instruction

Ronald S. Bultje rsbultje at gmail.com
Mon Jun 14 14:53:20 EEST 2021


Hi Alan,

On Mon, Jun 14, 2021 at 7:20 AM Alan Kelly <
alankelly-at-google.com at ffmpeg.org> wrote:

> Broadwell and later have fast gather instructions.
> ---
>  This is so that the avx2 version of ff_hscale8to15X which uses gather
>  instructions is only selected on machines where it will actually be
>  faster.
>

We've in the past typically done this with a bit in the cpuflags return
value. Can this be added there instead of being its own function?

Also, what is the cycle count of ssse3/avx2 implementation for this
specific function on Haswell? It would be good to note that in the
respective patch so that we understand why the check was added.

Ronald


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