Re: [FFmpeg-devel] [PATCH v2 2/2] swscale/aarch64: add hscale specializations

["Martin Storsjö" <martin@martin.st>]

On Wed, 25 May 2022, Swinney, Jonathan wrote:

> This patch adds code to support specializations of the hscale function and adds
> a specialization for filterSize == 4.
>
> ff_hscale8to15_4_neon is a complete rewrite. Since the main bottleneck here is
> loading the data from src, this data is loaded a whole block ahead and stored
> back to the stack to be loaded again with ld4. This arranges the data for most
> efficient use of the vector instructions and removes the need for completion
> adds at the end. The number of iterations of the C per iteration of the assembly
> is increased from 4 to 8, but because of the prefetching, there must be a
> special section without prefetching when dstW < 16.
>
> This improves speed on Graviton 2 (Neoverse N1) dramatically in the case where
> previously fs=8 would have been required.
>
> before: hscale_8_to_15__fs_8_dstW_512_neon: 1962.8
> after : hscale_8_to_15__fs_4_dstW_512_neon: 1220.9
>
> Signed-off-by: Jonathan Swinney <jswinney@amazon.com>
> ---
> libswscale/aarch64/hscale.S  | 172 ++++++++++++++++++++++++++++++++++-
> libswscale/aarch64/swscale.c |  40 ++++++--
> libswscale/utils.c           |   2 +-
> 3 files changed, 203 insertions(+), 11 deletions(-)
>
> -void ff_hscale_8_to_15_neon(SwsContext *c, int16_t *dst, int dstW,
> -                            const uint8_t *src, const int16_t *filter,
> -                            const int32_t *filterPos, int filterSize);
> +#define SCALE_FUNC(filter_n, from_bpc, to_bpc, opt) \
> +void ff_hscale ## from_bpc ## to ## to_bpc ## _ ## filter_n ## _ ## opt( \
> +                                                SwsContext *c, int16_t *data, \
> +                                                int dstW, const uint8_t *src, \
> +                                                const int16_t *filter, \
> +                                                const int32_t *filterPos, int filterSize)
> +#define SCALE_FUNCS(filter_n, opt) \
> +    SCALE_FUNC(filter_n,  8, 15, opt);
> +#define ALL_SCALE_FUNCS(opt) \
> +    SCALE_FUNCS(4, opt); \
> +    SCALE_FUNCS(8, opt); \
> +    SCALE_FUNCS(X8, opt)

Here, you still declare the -8 function which no longer is implemented.

Other than that, this patch looks fine I think.

// Martin

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