[FFmpeg-devel] [PATCH v3 1/2] swscale: rgb_to_yuv neon optimizations

[Martin Storsjö]

On Fri, 30 May 2025, Dmitriy Kovalenko wrote:

> I've found quite a few ways to optimize existing ffmpeg's rgb to yuv
> subsampled conversion. In this patch stack I'll try to
> improve the perofrmance.
>
> This particular set of changes is a small improvement to all the
> existing functions and macro. The biggest performance gain is
> coming from post loading increment of the pointer and immediate
> prefetching of the memory blocks and interleaving the multiplication shifting operations of
> different registers for better scheduling.
>
> Also changed a bunch of places where cmp + b.le was used instead
> of one instruction cbnz/tbnz and some other small cleanups.
>
> Here are checkasm results on the macbook pro with the latest M4 max
>
> <before>
>
> bgra_to_uv_1080_c:                                     257.5 ( 1.00x)
> bgra_to_uv_1080_neon:                                  211.9 ( 1.22x)
> bgra_to_uv_1920_c:                                     467.1 ( 1.00x)
> bgra_to_uv_1920_neon:                                  379.3 ( 1.23x)
> bgra_to_uv_half_1080_c:                                198.9 ( 1.00x)
> bgra_to_uv_half_1080_neon:                             125.7 ( 1.58x)
> bgra_to_uv_half_1920_c:                                346.3 ( 1.00x)
> bgra_to_uv_half_1920_neon:                             223.7 ( 1.55x)
>
> <after>
>
> bgra_to_uv_1080_c:                                     268.3 ( 1.00x)
> bgra_to_uv_1080_neon:                                  176.0 ( 1.53x)
> bgra_to_uv_1920_c:                                     456.6 ( 1.00x)
> bgra_to_uv_1920_neon:                                  307.7 ( 1.48x)
> bgra_to_uv_half_1080_c:                                193.2 ( 1.00x)
> bgra_to_uv_half_1080_neon:                              96.8 ( 2.00x)
> bgra_to_uv_half_1920_c:                                347.2 ( 1.00x)
> bgra_to_uv_half_1920_neon:                             182.6 ( 1.92x)
>
> With my proprietary test on IOS it gives around 70% of performance
> improvement converting bgra 1920x1920 image to yuv420p
>
> On my linux arm cortex-r processing the performance improvement not that
> visible but still consistently faster by 5-10% than the current
> implementation.
> ---
> libswscale/aarch64/input.S | 181 +++++++++++++++++++++++--------------
> 1 file changed, 112 insertions(+), 69 deletions(-)

This doesn't compile even on macOS any longer, what is this?

I will not respond to this thread any more until _every_ _single_ inline 
comment has been replied to and motivated, and until the prefetch 
intructions have split to a separate patch.

// Martin