[FFmpeg-devel] [PATCH 4/4] swscale/aarch64: add nv24/nv42 to yuv420p unscaled converter

[Ramiro Polla]

On Wed, Aug 14, 2024 at 7:21 PM Martin Storsjö <martin at martin.st> wrote:
> On Fri, 9 Aug 2024, Ramiro Polla wrote:
> > checkasm --bench for Raspberry Pi 5 Model B Rev 1.0:
> > nv24_yuv420p_128_c: 423.0
> > nv24_yuv420p_128_neon: 115.7
> > nv24_yuv420p_1920_c: 5939.5
> > nv24_yuv420p_1920_neon: 1339.7
> > nv42_yuv420p_128_c: 423.2
> > nv42_yuv420p_128_neon: 115.7
> > nv42_yuv420p_1920_c: 5907.5
> > nv42_yuv420p_1920_neon: 1342.5
> > ---
> > libswscale/aarch64/Makefile                |  1 +
> > libswscale/aarch64/swscale_unscaled.c      | 30 +++++++++
> > libswscale/aarch64/swscale_unscaled_neon.S | 75 ++++++++++++++++++++++
> > 3 files changed, 106 insertions(+)
> > create mode 100644 libswscale/aarch64/swscale_unscaled_neon.S
>
> > diff --git a/libswscale/aarch64/swscale_unscaled_neon.S b/libswscale/aarch64/swscale_unscaled_neon.S
> > new file mode 100644
> > index 0000000000..a206fda41f
> > --- /dev/null
> > +++ b/libswscale/aarch64/swscale_unscaled_neon.S
> > @@ -0,0 +1,75 @@
> > +/*
> > + * Copyright (c) 2024 Ramiro Polla
> > + *
> > + * This file is part of FFmpeg.
> > + *
> > + * FFmpeg is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2.1 of the License, or (at your option) any later version.
> > + *
> > + * FFmpeg is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with FFmpeg; if not, write to the Free Software
> > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> > + */
> > +
> > +#include "libavutil/aarch64/asm.S"
> > +
> > +function ff_nv24_to_yuv420p_chroma_neon, export=1
> > +// x0  uint8_t *dst1
> > +// x1  int dstStride1
> > +// x2  uint8_t *dst2
> > +// x3  int dstStride2
> > +// x4  const uint8_t *src
> > +// x5  int srcStride
> > +// w6  int w
> > +// w7  int h
> > +
> > +        uxtw            x1, w1
> > +        uxtw            x3, w3
> > +        uxtw            x5, w5
>
> You can often avoid the explicit uxtw instructions, if you can fold an
> uxtw attribute into the cases where the register is used. (If it's used
> often, it may be slightly more performant to do it upfront like this
> though, but often it can be omitted entirely.) And whenever you do an
> operation with a wN register as destination, the upper half of the
> register gets explicitly cleared, so these also may be avoided that way.
>
> > +
> > +        add             x9, x4, x5                  // x9 = src + srcStride
> > +        lsl             w5, w5, #1                  // srcStride *= 2
> > +
> > +1:
> > +        mov             w10, w6                     // w10 = w
> > +        mov             x11, x4                     // x11 = src1 (line 1)
> > +        mov             x12, x9                     // x12 = src2 (line 2)
> > +        mov             x13, x0                     // x13 = dst1 (dstU)
> > +        mov             x14, x2                     // x14 = dst2 (dstV)
> > +
> > +2:
> > +        ld2             { v0.16b, v1.16b }, [x11], #32 // v0 = U1, v1 = V1
> > +        ld2             { v2.16b, v3.16b }, [x12], #32 // v2 = U2, v3 = V2
> > +
> > +        uaddlp          v0.8h, v0.16b               // pairwise add U1 into v0
> > +        uaddlp          v1.8h, v1.16b               // pairwise add V1 into v1
> > +        uadalp          v0.8h, v2.16b               // pairwise add U2, accumulate into v0
> > +        uadalp          v1.8h, v3.16b               // pairwise add V2, accumulate into v1
> > +
> > +        shrn            v0.8b, v0.8h, #2            // divide by 4
> > +        shrn            v1.8b, v1.8h, #2            // divide by 4
> > +
> > +        st1             { v0.8b }, [x13], #8        // store U into dst1
> > +        st1             { v1.8b }, [x14], #8        // store V into dst2
> > +
> > +        subs            w10, w10, #8
> > +        b.gt            2b
> > +
> > +        // next row
> > +        add             x4, x4, x5                  // src1 += srcStride * 2
> > +        add             x9, x9, x5                  // src2 += srcStride * 2
> > +        add             x0, x0, x1                  // dst1 += dstStride1
> > +        add             x2, x2, x3                  // dst2 += dstStride2
>
> It's often possible to avoid the extra step of moving the pointers back
> into the the x11/x12/x13/x14 registers, if you subtract the width from the
> stride at the start of the function. Then you don't need two separate
> registers for each pointer, and shortens dependency chain when moving on
> to the next line.
>
> If the width can be any uneven value, but we in practice write in
> increments of 8 pixels, you may need to align the width up to 8 before
> using it to decrement the stride that way though.

Thank you for the review. New patch attached.
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