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

[Krzysztof Pyrkosz]

On Sat, Feb 08, 2025 at 01:59:32AM +0100, Lynne wrote:
> 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?

Here are my benchmarks on Raspberry Pi 3B+.

Before:
deemphasis_neon:                                      4121.8 ( 2.11x)
postfilter_15_neon:                                   9405.2 ( 2.46x)
postfilter_512_neon:                                  9457.0 ( 2.44x)
postfilter_1022_neon:                                 9398.0 ( 2.46x)

After:
deemphasis_neon:                                      4135.8 ( 2.10x)
postfilter_15_neon:                                   7967.2 ( 2.90x)
postfilter_512_neon:                                  7980.2 ( 2.89x)
postfilter_1022_neon:                                 7980.0 ( 2.89x)

Krzysztof