Re: [FFmpeg-devel] [PATCH 1/7] lavc/me_cmp: R-V V pix_abs

From: flow gg <hlefthleft@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/7] lavc/me_cmp: R-V V pix_abs
Date: Fri, 9 Feb 2024 06:39:38 +0800
Message-ID: <CAEa-L+v+bkE7_JS9Ek8gD8dTDiO4QNQXHNiK8QBLNB0Z8KYFng@mail.gmail.com> (raw)
In-Reply-To: <6034609.ydglWbVfdg@basile.remlab.net>

From my understanding, to use larger group multipliers, one needs to
utilize vlse64 (8x8) vlse128 (16x16).

However, due to the use in tests of

ptr = img2 + y * WIDTH + x;
d2 = call_ref(NULL, img1, ptr, WIDTH, h);
d1 = call_new(NULL, img1, ptr, WIDTH, h);

will get:  pix_abs_1_0_rvv_i32 (fatal signal 7: Bus error)

Because it can only load according to e8, it seems there's no way to use
larger group multipliers.

Rémi Denis-Courmont <remi@remlab.net> 于2024年2月9日周五 03:41写道：

> Le keskiviikkona 7. helmikuuta 2024, 2.01.23 EET flow gg a écrit :
> > I think in most cases it is like this, but specifically for this
> function,
> > using Reduction only once would be slower.
> >
> > The currently submitted version roughly takes:
> > pix_abs_0_0_rvv_i32: 136.2
> >
> > The version that uses Reduction only once takes:
> > pix_abs_0_0_rvv_i32: 169.2
>
> You're only using one vector and half a vector respectively, so the
> logarithmic time of the sum is relatively small.
>
> But are you sure that it wouldn't be faster to process multiple rows and
> larger group multiplers?
>
> > Here is the implementation of the version that uses it only once:
> >
> > func ff_pix_abs16_temp_rvv, zve32x
> >         vsetivli        zero, 16, e32, m4, ta, ma
> >         vmv.v.i         v24, 0
> >         vmv.s.x         v0, zero
> > 1:
> >         vsetvli         zero, zero, e8, m1, tu, ma
> >         vle8.v          v4, (a1)
> >         vle8.v          v12, (a2)
> >         addi            a4, a4, -1
> >         vwsubu.vv       v16, v4, v12
> >         add             a1, a1, a3
> >         vwsubu.vv       v20, v12, v4
> >         vsetvli         zero, zero, e16, m2, tu, ma
> >         vmax.vv         v16, v16, v20
> >         add             a2, a2, a3
> >         vwadd.wv        v24, v24, v16
> >         bnez            a4, 1b
> >
> >         vsetvli         zero, zero, e32, m4, ta, ma
> >         vwredsumu.vs    v0, v24, v0
> >         vmv.x.s         a0, v0
> >         ret
> > endfunc
> >
> > Rémi Denis-Courmont <remi@remlab.net> 于2024年2月7日周三 00:58写道：
> >
> > > Hi,
> > >
> > > To sum a vector, you should only reduce once at the end of the
> function,
> > > c.f.
> > > how it's done in existing scalar products. Reduction instructions are
> > > (intrinsically) slow.
> > >
> > > --
> > > Rémi Denis-Courmont
> > > http://www.remlab.net/
> >
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel@ffmpeg.org
> > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >
> > To unsubscribe, visit link above, or email
> > ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
>
>
> --
> 雷米‧德尼-库尔蒙
> http://www.remlab.net/
>
>
>
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