[FFmpeg-devel] [PATCH] af_afir: RISC-V V fcmul_add

[flow gg]

>>> please pad mnemonics to at least 8 columns for consistency

okay, changed

>>> It seems that you could just as well use vlseg2 without register
stride, no?

yes, vlseg will better, changed

>>> Note that you could do the double versions with very little extra
efforts.

okay

>>> But really, DO NOT use a fixed vector length here. At best, you're
wasting half
>>> the vector width. Your input has a variable size, use it.

okay, changed

>>> I'm a bit surprised that the performance improves this much,
considering that
>>> the C910 is notoriously bad at both segmented strided loads. It might
be that
>>> the C versions is just very bad due to lack of aliasing optimisations.

thanks, You reminded me.
Sorry I had forgotten that there was a problem..
A few days ago, I wanted to try running some existing benchmarks,

```
tests/checkasm/checkasm --bench --test=aacpsdsp
tests/checkasm/checkasm --bench --test=alacdsp
tests/checkasm/checkasm --bench --test=audiodsp
tests/checkasm/checkasm --bench --test=g722dsp
tests/checkasm/checkasm --bench --test=vorbisdsp
tests/checkasm/checkasm --bench --test=float_dsp
tests/checkasm/checkasm --bench --test=fixed_dsp
tests/checkasm/checkasm --bench --test=af_afir
```

but they all returned 0.0.

For example,

```
butterflies_float_c: 0.0
butterflies_float_rvv_f32: 0.0
scalarproduct_float_c: 0.0
scalarproduct_float_rvv_f32: 0.0
vector_dmac_scalar_c: 0.0
vector_dmac_scalar_rvv_f64: 0.0
...
```

I tried changing the -O3 in configure to -O2 or -O1, but still got 0.0.

Only by changing to -O0 did I receive non-zero results.

So, the benchmark I conducted was based on this, and I obtained the initial
results…

fcmul_add_c: 19.7
fcmul_add_rvv_f32: 6.7

Rémi Denis-Courmont <remi at remlab.net> 于2023年9月27日周三 02:44写道：

> Le tiistaina 26. syyskuuta 2023, 21.40.12 EEST Paul B Mahol a écrit :
> > On Tue, Sep 26, 2023 at 8:35 PM Rémi Denis-Courmont <remi at remlab.net>
> wrote:
> > > Le tiistaina 26. syyskuuta 2023, 12.24.58 EEST flow gg a écrit :
> > > > benchmark:
> > > > fcmul_add_c: 19.7
> > > > fcmul_add_rvv_f32: 6.7
> > >
> > > Nit: please pad mnemonics to at least 8 columns for consistency.
> > >
> > > I'm a bit surprised that the performance improves this much,
> considering
> > > that
> > > the C910 is notoriously bad at both segmented strided loads. It might
> be
> > > that
> > > the C versions is just very bad due to lack of aliasing optimisations.
> Oh
> > > well.
> >
> > What you mean exactly that C version is missing?
>
> The C version does not have any restrict qualifier. This potentially
> prevents
> the C compiler from unrolling. Adding the keyword can improve performance
> gains of 20-30% on RISC-V scalar floating point.
>
> That said, sometimes you can't validly use restrict, and you simply can't
> tell
> the C compiler how to optimise properly. In those cases, even scalar
> floating
> point optimisations improve performance.
>
> --
> Rémi Denis-Courmont
> http://www.remlab.net/
>
>
>
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