Re: [FFmpeg-devel] [PATCH v2 12/15] avfilter/vf_bwdif: Add a filter_line3 method for optimisation

[Thomas Mundt <tmundt75@gmail.com>]

Am Mo., 3. Juli 2023 um 10:27 Uhr schrieb John Cox <jc@kynesim.co.uk>:

> On Mon, 3 Jul 2023 00:12:46 +0300 (EEST), you wrote:
>
> >On Sun, 2 Jul 2023, Thomas Mundt wrote:
> >
> >> Am So., 2. Juli 2023 um 14:34 Uhr schrieb John Cox <jc@kynesim.co.uk>:
> >>       Add an optional filter_line3 to the available optimisations.
> >>
> >>       filter_line3 is equivalent to filter_line, memcpy, filter_line
> >>
> >>       filter_line shares quite a number of loads and some calculations
> >>       in
> >>       common with its next iteration and testing shows that using
> >>       aarch64
> >>       neon filter_line3s performance is 30% better than two
> >>       filter_lines
> >>       and a memcpy.
> >>
> >>       Signed-off-by: John Cox <jc@kynesim.co.uk>
> >>       ---
> >>        libavfilter/bwdif.h    |  7 +++++++
> >>        libavfilter/vf_bwdif.c | 31 +++++++++++++++++++++++++++++++
> >>        2 files changed, 38 insertions(+)
> >>
> >>       diff --git a/libavfilter/bwdif.h b/libavfilter/bwdif.h
> >>       index cce99953f3..496cec72ef 100644
> >>       --- a/libavfilter/bwdif.h
> >>       +++ b/libavfilter/bwdif.h
> >>       @@ -35,6 +35,9 @@ typedef struct BWDIFContext {
> >>            void (*filter_edge)(void *dst, void *prev, void *cur, void
> >>       *next,
> >>                                int w, int prefs, int mrefs, int
> >>       prefs2, int mrefs2,
> >>                                int parity, int clip_max, int spat);
> >>       +    void (*filter_line3)(void *dst, int dstride,
> >>       +                         const void *prev, const void *cur,
> >>       const void *next, int prefs,
> >>       +                         int w, int parity, int clip_max);
> >>        } BWDIFContext;
> >>
> >>        void ff_bwdif_init_filter_line(BWDIFContext *bwdif, int
> >>       bit_depth);
> >>       @@ -53,4 +56,8 @@ void ff_bwdif_filter_line_c(void *dst1, void
> >>       *prev1, void *cur1, void *next1,
> >>                                    int prefs3, int mrefs3, int prefs4,
> >>       int mrefs4,
> >>                                    int parity, int clip_max);
> >>
> >>       +void ff_bwdif_filter_line3_c(void * dst1, int d_stride,
> >>       +                             const void * prev1, const void *
> >>       cur1, const void * next1, int s_stride,
> >>       +                             int w, int parity, int clip_max);
> >>       +
> >>        #endif /* AVFILTER_BWDIF_H */
> >>       diff --git a/libavfilter/vf_bwdif.c b/libavfilter/vf_bwdif.c
> >>       index 26349da1fd..52bc676cf8 100644
> >>       --- a/libavfilter/vf_bwdif.c
> >>       +++ b/libavfilter/vf_bwdif.c
> >>       @@ -150,6 +150,31 @@ void ff_bwdif_filter_line_c(void *dst1,
> >>       void *prev1, void *cur1, void *next1,
> >>            FILTER2()
> >>        }
> >>
> >>       +#define NEXT_LINE()\
> >>       +    dst += d_stride; \
> >>       +    prev += prefs; \
> >>       +    cur  += prefs; \
> >>       +    next += prefs;
> >>       +
> >>       +void ff_bwdif_filter_line3_c(void * dst1, int d_stride,
> >>       +                             const void * prev1, const void *
> >>       cur1, const void * next1, int s_stride,
> >>       +                             int w, int parity, int clip_max)
> >>       +{
> >>       +    const int prefs = s_stride;
> >>       +    uint8_t * dst  = dst1;
> >>       +    const uint8_t * prev = prev1;
> >>       +    const uint8_t * cur  = cur1;
> >>       +    const uint8_t * next = next1;
> >>       +
> >>       +    ff_bwdif_filter_line_c(dst, (void*)prev, (void*)cur,
> >>       (void*)next, w,
> >>       +                           prefs, -prefs, prefs * 2, - prefs *
> >>       2, prefs * 3, -prefs * 3, prefs * 4, -prefs * 4, parity,
> >>       clip_max);
> >>       +    NEXT_LINE();
> >>       +    memcpy(dst, cur, w);
> >>       +    NEXT_LINE();
> >>       +    ff_bwdif_filter_line_c(dst, (void*)prev, (void*)cur,
> >>       (void*)next, w,
> >>       +                           prefs, -prefs, prefs * 2, - prefs *
> >>       2, prefs * 3, -prefs * 3, prefs * 4, -prefs * 4, parity,
> >>       clip_max);
> >>       +}
> >>       +
> >>        void ff_bwdif_filter_edge_c(void *dst1, void *prev1, void
> >>       *cur1, void *next1,
> >>                                    int w, int prefs, int mrefs, int
> >>       prefs2, int mrefs2,
> >>                                    int parity, int clip_max, int spat)
> >>       @@ -244,6 +269,11 @@ static int filter_slice(AVFilterContext
> >>       *ctx, void *arg, int jobnr, int nb_jobs)
> >>                                       refs << 1, -(refs << 1),
> >>                                       td->parity ^ td->tff, clip_max,
> >>                                       (y < 2) || ((y + 3) > td->h) ? 0
> >>       : 1);
> >>       +            } else if (s->filter_line3 && y + 2 < slice_end &&
> >>       y + 6 < td->h) {
> >>       +                s->filter_line3(dst,
> >>       td->frame->linesize[td->plane],
> >>       +                                prev, cur, next, linesize,
> >>       td->w,
> >>       +                                td->parity ^ td->tff,
> >>       clip_max);
> >>       +                y += 2;
> >>                    } else {
> >>                        s->filter_line(dst, prev, cur, next, td->w,
> >>                                       refs, -refs, refs << 1, -(refs
> >>       << 1),
> >>
> >>
> >> Maybe I'm missing something, but doesn't this kick out most of the x86
> SIMD
> >> optimization because there is no filter_line3?
> >
> >It looks to me like it doesn't; it adds a new optional function pointer,
> >but the reference C function isn't set. So by default (and on x86)
> >filter_line3 is null, and the old assembly optimized codepaths are used.
> >But if an architecture does implement filter_line3, that's used instead
> of
> >filter_line.
>
> Indeed - that is both the intent and what appears to occur when I test
> it. I'd have made the C line3 function call down to line if I had any
> context that allowed it but passing a real context seemed against the
> spirit of nearly all the asm optimisations.
>

You´re right. Thanks.
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