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

[flow gg <hlefthleft@gmail.com>]

The issue here is that any load greater than e8 will fail the test(Bus
error), so it cannot use vlse64 or similar methods...

Rémi Denis-Courmont <remi@remlab.net> 于2024年2月9日周五 18:32写道：

>
>
> Le 9 février 2024 00:39:38 GMT+02:00, flow gg <hlefthleft@gmail.com> a
> écrit :
> >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.
>
> vlse128.v requires 128-bit elements, which no hardware supports. vlse64.v
> works just fine; we're already using it. There's also the possibility of
> segmented strided loads, or simply multiple unit loads.
>
> In any case, unrolling one way or other should improve performance.
>
>
> >
> >
> >
> >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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> >>
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