Re: [FFmpeg-devel] [PATCH] avcodec/aarch64/opusdsp_neon: Simplify opus_postfilter_neon

[Lynne <dev@lynne.ee>]

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On 07/02/2025 20:42, Krzysztof Pyrkosz via ffmpeg-devel wrote:
> This change removes one extra floating point operation and simplifies
> load operations at the beginning of the loop by using dedicated register
> for each of the 5 pointers and interleaving it with calculations. The
> first case seems to be a bit slower, but the performance increase is
> substantial in the other two.
> 
> A78 before:
> postfilter_15_neon:                                   1684.8 ( 4.23x)
> postfilter_512_neon:                                  1395.5 ( 5.10x)
> postfilter_1022_neon:                                 1357.0 ( 5.25x)
> 
> After:
> postfilter_15_neon:                                   1742.2 ( 4.09x)
> postfilter_512_neon:                                  1169.8 ( 6.09x)
> postfilter_1022_neon:                                 1160.0 ( 6.12x)
> 
> 
> A72 before:
> postfilter_15_neon:                                   3144.8 ( 2.39x)
> postfilter_512_neon:                                  3141.2 ( 2.39x)
> postfilter_1022_neon:                                 3230.0 ( 2.33x)
> 
> After:
> postfilter_15_neon:                                   2847.8 ( 2.64x)
> postfilter_512_neon:                                  2877.8 ( 2.61x)
> postfilter_1022_neon:                                 2837.2 ( 2.65x)
> 
> 
> x13s before:
> postfilter_15_neon:                                   1615.4 ( 2.61x)
> postfilter_512_neon:                                   963.1 ( 4.39x)
> postfilter_1022_neon:                                  963.6 ( 4.39x)
> 
> After:
> postfilter_15_neon:                                   1749.6 ( 2.41x)
> postfilter_512_neon:                                   707.1 ( 5.97x)
> postfilter_1022_neon:                                  706.1 ( 5.99x)
> 
> 
> Krzysztof
> 
> ---
>   libavcodec/aarch64/opusdsp_neon.S | 31 ++++++++++++-------------------
>   1 file changed, 12 insertions(+), 19 deletions(-)
> 
> diff --git a/libavcodec/aarch64/opusdsp_neon.S b/libavcodec/aarch64/opusdsp_neon.S
> index 253825aa61..990fc44c70 100644
> --- a/libavcodec/aarch64/opusdsp_neon.S
> +++ b/libavcodec/aarch64/opusdsp_neon.S
> @@ -55,35 +55,28 @@ endfunc
>   
>   function ff_opus_postfilter_neon, export=1
>           ld1             {v0.4s}, [x2]
> +        sub             x5, x0, w1, sxtw #2
> +        sub             x1, x5, #8
>           dup             v1.4s, v0.s[1]
>           dup             v2.4s, v0.s[2]
>           dup             v0.4s, v0.s[0]
>   
> -        add             w1, w1, #2
> -        sub             x1, x0, x1, lsl #2
> -
> -        ld1             {v3.4s}, [x1]
> +        ld1             {v3.4s}, [x1], #16
> +        sub             x4, x5, #4
> +        add             x6, x5, #4
>           fmul            v3.4s, v3.4s, v2.4s
>   
> -1:      add             x1, x1, #4
> -        ld1             {v4.4s}, [x1]
> -        add             x1, x1, #4
> -        ld1             {v5.4s}, [x1]
> -        add             x1, x1, #4
> -        ld1             {v6.4s}, [x1]
> -        add             x1, x1, #4
> -        ld1             {v7.4s}, [x1]
> -
> +1:      ld1             {v7.4s}, [x1], #16
> +        ld1             {v4.4s}, [x4], #16
>           fmla            v3.4s, v7.4s, v2.4s
> +        ld1             {v6.4s}, [x6], #16
> +        ld1             {v5.4s}, [x5], #16
>           fadd            v6.4s, v6.4s, v4.4s
> +        fmla            v3.4s, v5.4s, v0.4s
>   
>           ld1             {v4.4s}, [x0]
> -        fmla            v4.4s, v5.4s, v0.4s
> -
> -        fmul            v6.4s, v6.4s, v1.4s
> -        fadd            v6.4s, v6.4s, v3.4s
> -
> -        fadd            v4.4s, v4.4s, v6.4s
> +        fmla            v3.4s, v6.4s, v1.4s
> +        fadd            v4.4s, v4.4s, v3.4s
>           fmul            v3.4s, v7.4s, v2.4s
>   
>           st1             {v4.4s}, [x0], #16

This function was written and optimized for A53 cores. The fmla chain is 
very performance sensitive on in-order CPUs?
Could you post a perf difference from an in-order CPU?

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