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

[Rémi Denis-Courmont]

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/