[FFmpeg-devel] [PATCH] pixblockdsp: Use memcpy for get_pixels_16_c

[Ganesh Ajjanagadde]

On Tue, Oct 20, 2015 at 4:20 PM, Timothy Gu <timothygu99 at gmail.com> wrote:
> Before:
>   15543 decicycles in get_pixels, 4193214 runs,   1090 skips
> After:
>    5713 decicycles in get_pixels, 8387564 runs,   1044 skips
> ---
>  libavcodec/pixblockdsp.c          | 36 ++++++++++++++++++++++++++++++-----
>  libavcodec/pixblockdsp_template.c | 40 ---------------------------------------
>  2 files changed, 31 insertions(+), 45 deletions(-)
>  delete mode 100644 libavcodec/pixblockdsp_template.c
>
> diff --git a/libavcodec/pixblockdsp.c b/libavcodec/pixblockdsp.c
> index 322e1dd..0f23d8a 100644
> --- a/libavcodec/pixblockdsp.c
> +++ b/libavcodec/pixblockdsp.c
> @@ -23,12 +23,38 @@
>  #include "avcodec.h"
>  #include "pixblockdsp.h"
>
> -#define BIT_DEPTH 16
> -#include "pixblockdsp_template.c"
> -#undef BIT_DEPTH
> +static void get_pixels_16_c(int16_t *av_restrict block, const uint8_t *pixels,
> +                            ptrdiff_t line_size)
> +{
> +    memcpy(block + 0 * 8, pixels + 0 * line_size, sizeof(int16_t) * 8);
> +    memcpy(block + 1 * 8, pixels + 1 * line_size, sizeof(int16_t) * 8);
> +    memcpy(block + 2 * 8, pixels + 2 * line_size, sizeof(int16_t) * 8);
> +    memcpy(block + 3 * 8, pixels + 3 * line_size, sizeof(int16_t) * 8);
> +    memcpy(block + 4 * 8, pixels + 4 * line_size, sizeof(int16_t) * 8);
> +    memcpy(block + 5 * 8, pixels + 5 * line_size, sizeof(int16_t) * 8);
> +    memcpy(block + 6 * 8, pixels + 6 * line_size, sizeof(int16_t) * 8);
> +    memcpy(block + 7 * 8, pixels + 7 * line_size, sizeof(int16_t) * 8);
> +}
> +
> +static void get_pixels_8_c(int16_t *av_restrict block, const uint8_t *pixels,
> +                           ptrdiff_t line_size)
> +{
> +    int i;
>
> -#define BIT_DEPTH 8
> -#include "pixblockdsp_template.c"
> +    /* read the pixels */
> +    for (i = 0; i < 8; i++) {
> +        block[0] = pixels[0];
> +        block[1] = pixels[1];
> +        block[2] = pixels[2];
> +        block[3] = pixels[3];
> +        block[4] = pixels[4];
> +        block[5] = pixels[5];
> +        block[6] = pixels[6];
> +        block[7] = pixels[7];
> +        pixels  += line_size;
> +        block   += 8;
> +    }
> +}

out of curiosity: do you get gains for get_pixels_8_c as well? What I
am surprised to see is that even with the restrict keyword, a compiler
does not optimize the assignments within the loop to some sort of
block assignment (which I assume memcpy is doing).

>
>  static void diff_pixels_c(int16_t *av_restrict block, const uint8_t *s1,
>                            const uint8_t *s2, int stride)
> diff --git a/libavcodec/pixblockdsp_template.c b/libavcodec/pixblockdsp_template.c
> deleted file mode 100644
> index d1e9102..0000000
> --- a/libavcodec/pixblockdsp_template.c
> +++ /dev/null
> @@ -1,40 +0,0 @@
> -/*
> - * 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 "bit_depth_template.c"
> -
> -static void FUNCC(get_pixels)(int16_t *av_restrict block, const uint8_t *_pixels,
> -                              ptrdiff_t line_size)
> -{
> -    const pixel *pixels = (const pixel *) _pixels;
> -    int i;
> -
> -    /* read the pixels */
> -    for (i = 0; i < 8; i++) {
> -        block[0] = pixels[0];
> -        block[1] = pixels[1];
> -        block[2] = pixels[2];
> -        block[3] = pixels[3];
> -        block[4] = pixels[4];
> -        block[5] = pixels[5];
> -        block[6] = pixels[6];
> -        block[7] = pixels[7];
> -        pixels  += line_size / sizeof(pixel);
> -        block   += 8;
> -    }
> -}
> --
> 1.9.1
>
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