[FFmpeg-devel] [PATCH v3 2/2] swscale/aarch64: add hscale specializations
J. Dekker
jdek at itanimul.li
Thu May 26 13:58:39 EEST 2022
I was working on an improvement for this function but seems you finished before me. To avoid duplicating further work, do you have plans to implement hscale 9-16 to 15, and hscale 8-16 to 19? Or may I base those further functions on this patch (given your version is faster than mine currently)?
And a few stylistic comments:
On 26 May 2022, at 4:02, 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 at amazon.com>
> ---
> libswscale/aarch64/hscale.S | 172 ++++++++++++++++++++++++++++++++++-
> libswscale/aarch64/swscale.c | 39 ++++++--
> libswscale/utils.c | 2 +-
> 3 files changed, 202 insertions(+), 11 deletions(-)
>
> diff --git a/libswscale/aarch64/hscale.S b/libswscale/aarch64/hscale.S
> index da34f1cb8d..c5fa146bcf 100644
> --- a/libswscale/aarch64/hscale.S
> +++ b/libswscale/aarch64/hscale.S
> @@ -1,5 +1,7 @@
> /*
> * Copyright (c) 2016 Clément Bœsch <clement stupeflix.com>
> + * Copyright (c) 2019-2021 Sebastian Pop <spop at amazon.com>
> + * Copyright (c) 2022 Jonathan Swinney <jswinney at amazon.com>
> *
> * This file is part of FFmpeg.
> *
> @@ -20,7 +22,25 @@
>
> #include "libavutil/aarch64/asm.S"
>
> -function ff_hscale_8_to_15_neon, export=1
> +/*
> +;-----------------------------------------------------------------------------
> +; horizontal line scaling
> +;
> +; void hscale<source_width>to<intermediate_nbits>_<filterSize>_<opt>
> +; (SwsContext *c, int{16,32}_t *dst,
> +; int dstW, const uint{8,16}_t *src,
> +; const int16_t *filter,
> +; const int32_t *filterPos, int filterSize);
> +;
> +; Scale one horizontal line. Input is either 8-bit width or 16-bit width
> +; ($source_width can be either 8, 9, 10 or 16, difference is whether we have to
> +; downscale before multiplying). Filter is 14 bits. Output is either 15 bits
> +; (in int16_t) or 19 bits (in int32_t), as given in $intermediate_nbits. Each
> +; output pixel is generated from $filterSize input pixels, the position of
> +; the first pixel is given in filterPos[nOutputPixel].
> +;----------------------------------------------------------------------------- */
> +
> +function ff_hscale8to15_X8_neon, export=1
> sbfiz x7, x6, #1, #32 // filterSize*2 (*2 because int16)
> 1: ldr w8, [x5], #4 // filterPos[idx]
> ldr w0, [x5], #4 // filterPos[idx + 1]
> @@ -70,3 +90,153 @@ function ff_hscale_8_to_15_neon, export=1
> b.gt 1b // loop until end of line
> ret
> endfunc
> +
> +function ff_hscale8to15_4_neon, export=1
> +// x0 SwsContext *c (not used)
> +// x1 int16_t *dst
> +// x2 int dstW
> +// x3 const uint8_t *src
> +// x4 const int16_t *filter
> +// x5 const int32_t *filterPos
> +// x6 int filterSize
> +// x8-x15 registers for gathering src data
> +
> +// v0 madd accumulator 4S
> +// v1-v4 filter values (16 bit) 8H
> +// v5 madd accumulator 4S
> +// v16-v19 src values (8 bit) 8B
> +
> +// This implementation has 4 sections:
> +// 1. Prefetch src data
> +// 2. Interleaved prefetching src data and madd
> +// 3. Complete madd
> +// 4. Complete remaining iterations when dstW % 8 != 0
> +
> + add sp, sp, #-32 // allocate 32 bytes
Why not just use sub here?
> on the stack
> + cmp w2, #16 // if dstW <16, skip to the last block used for wrapping up
> + b.lt 2f
> +
> + // load 8 values from filterPos to be used as offsets into src
> + ldp w8, w9, [x5] // filterPos[idx + 0], [idx + 1]
> + ldp w10, w11, [x5, #8] // filterPos[idx + 2], [idx + 3]
> + ldp w12, w13, [x5, #16] // filterPos[idx + 4], [idx + 5]
> + ldp w14, w15, [x5, #24] // filterPos[idx + 6], [idx + 7]
> + add x5, x5, #32 // advance filterPos
> +
> + // gather random access data from src into contiguous memory
> + ldr w8, [x3, w8, UXTW] // src[filterPos[idx + 0]][0..3]
Current asm code has lowercase uxtw, would prefer to keep it consistent.
> + ldr w9, [x3, w9, UXTW] // src[filterPos[idx + 1]][0..3]
> + ldr w10, [x3, w10, UXTW] // src[filterPos[idx + 2]][0..3]
> + ldr w11, [x3, w11, UXTW] // src[filterPos[idx + 3]][0..3]
> + ldr w12, [x3, w12, UXTW] // src[filterPos[idx + 4]][0..3]
> + ldr w13, [x3, w13, UXTW] // src[filterPos[idx + 5]][0..3]
> + ldr w14, [x3, w14, UXTW] // src[filterPos[idx + 6]][0..3]
> + ldr w15, [x3, w15, UXTW] // src[filterPos[idx + 7]][0..3]
> + stp w8, w9, [sp] // *scratch_mem = { src[filterPos[idx + 0]][0..3], src[filterPos[idx + 1]][0..3] }
> + stp w10, w11, [sp, #8] // *scratch_mem = { src[filterPos[idx + 2]][0..3], src[filterPos[idx + 3]][0..3] }
> + stp w12, w13, [sp, #16] // *scratch_mem = { src[filterPos[idx + 4]][0..3], src[filterPos[idx + 5]][0..3] }
> + stp w14, w15, [sp, #24] // *scratch_mem = { src[filterPos[idx + 6]][0..3], src[filterPos[idx + 7]][0..3] }
> +
> +1:
> + ld4 {v16.8B, v17.8B, v18.8B, v19.8B}, [sp] // transpose 8 bytes each from src into 4 registers
Same with format specifiers being lower case, i.e. v16.8b
> +
> + // load 8 values from filterPos to be used as offsets into src
> + ldp w8, w9, [x5] // filterPos[idx + 0][0..3], [idx + 1][0..3], next iteration
> + ldp w10, w11, [x5, #8] // filterPos[idx + 2][0..3], [idx + 3][0..3], next iteration
> + ldp w12, w13, [x5, #16] // filterPos[idx + 4][0..3], [idx + 5][0..3], next iteration
> + ldp w14, w15, [x5, #24] // filterPos[idx + 6][0..3], [idx + 7][0..3], next iteration
> +
> + movi v0.2D, #0 // Clear madd accumulator for idx 0..3
> + movi v5.2D, #0 // Clear madd accumulator for idx 4..7
> +
> + ld4 {v1.8H, v2.8H, v3.8H, v4.8H}, [x4], #64 // load filter idx + 0..7
> +
> + add x5, x5, #32 // advance filterPos
> +
> + // interleaved SIMD and prefetching intended to keep ld/st and vector pipelines busy
> + uxtl v16.8H, v16.8B // unsigned extend long, covert src data to 16-bit
> + uxtl v17.8H, v17.8B // unsigned extend long, covert src data to 16-bit
> + ldr w8, [x3, w8, UXTW] // src[filterPos[idx + 0]], next iteration
> + ldr w9, [x3, w9, UXTW] // src[filterPos[idx + 1]], next iteration
> + uxtl v18.8H, v18.8B // unsigned extend long, covert src data to 16-bit
> + uxtl v19.8H, v19.8B // unsigned extend long, covert src data to 16-bit
> + ldr w10, [x3, w10, UXTW] // src[filterPos[idx + 2]], next iteration
> + ldr w11, [x3, w11, UXTW] // src[filterPos[idx + 3]], next iteration
> +
> + smlal v0.4S, v1.4H, v16.4H // multiply accumulate inner loop j = 0, idx = 0..3
> + smlal v0.4S, v2.4H, v17.4H // multiply accumulate inner loop j = 1, idx = 0..3
> + ldr w12, [x3, w12, UXTW] // src[filterPos[idx + 4]], next iteration
> + ldr w13, [x3, w13, UXTW] // src[filterPos[idx + 5]], next iteration
> + smlal v0.4S, v3.4H, v18.4H // multiply accumulate inner loop j = 2, idx = 0..3
> + smlal v0.4S, v4.4H, v19.4H // multiply accumulate inner loop j = 3, idx = 0..3
> + ldr w14, [x3, w14, UXTW] // src[filterPos[idx + 6]], next iteration
> + ldr w15, [x3, w15, UXTW] // src[filterPos[idx + 7]], next iteration
> +
> + smlal2 v5.4S, v1.8H, v16.8H // multiply accumulate inner loop j = 0, idx = 4..7
> + smlal2 v5.4S, v2.8H, v17.8H // multiply accumulate inner loop j = 1, idx = 4..7
> + stp w8, w9, [sp] // *scratch_mem = { src[filterPos[idx + 0]][0..3], src[filterPos[idx + 1]][0..3] }
> + stp w10, w11, [sp, #8] // *scratch_mem = { src[filterPos[idx + 2]][0..3], src[filterPos[idx + 3]][0..3] }
> + smlal2 v5.4S, v3.8H, v18.8H // multiply accumulate inner loop j = 2, idx = 4..7
> + smlal2 v5.4S, v4.8H, v19.8H // multiply accumulate inner loop j = 3, idx = 4..7
> + stp w12, w13, [sp, #16] // *scratch_mem = { src[filterPos[idx + 4]][0..3], src[filterPos[idx + 5]][0..3] }
> + stp w14, w15, [sp, #24] // *scratch_mem = { src[filterPos[idx + 6]][0..3], src[filterPos[idx + 7]][0..3] }
> +
> + sub w2, w2, #8 // dstW -= 8
> + sqshrn v0.4H, v0.4S, #7 // shift and clip the 2x16-bit final values
> + sqshrn v1.4H, v5.4S, #7 // shift and clip the 2x16-bit final values
> + st1 {v0.4H, v1.4H}, [x1], #16 // write to dst[idx + 0..7]
> + cmp w2, #16 // continue on main loop if there are at least 16 iterations left
> + b.ge 1b
> +
> + // last full iteration
> + ld4 {v16.8B, v17.8B, v18.8B, v19.8B}, [sp]
> + ld4 {v1.8H, v2.8H, v3.8H, v4.8H}, [x4], #64 // load filter idx + 0..7
> +
> + movi v0.2D, #0 // Clear madd accumulator for idx 0..3
> + movi v5.2D, #0 // Clear madd accumulator for idx 4..7
> +
> + uxtl v16.8H, v16.8B // unsigned extend long, covert src data to 16-bit
> + uxtl v17.8H, v17.8B // unsigned extend long, covert src data to 16-bit
> + uxtl v18.8H, v18.8B // unsigned extend long, covert src data to 16-bit
> + uxtl v19.8H, v19.8B // unsigned extend long, covert src data to 16-bit
> +
> + smlal v0.4S, v1.4H, v16.4H // multiply accumulate inner loop j = 0, idx = 0..3
> + smlal v0.4S, v2.4H, v17.4H // multiply accumulate inner loop j = 1, idx = 0..3
> + smlal v0.4S, v3.4H, v18.4H // multiply accumulate inner loop j = 2, idx = 0..3
> + smlal v0.4S, v4.4H, v19.4H // multiply accumulate inner loop j = 3, idx = 0..3
> +
> + smlal2 v5.4S, v1.8H, v16.8H // multiply accumulate inner loop j = 0, idx = 4..7
> + smlal2 v5.4S, v2.8H, v17.8H // multiply accumulate inner loop j = 1, idx = 4..7
> + smlal2 v5.4S, v3.8H, v18.8H // multiply accumulate inner loop j = 2, idx = 4..7
> + smlal2 v5.4S, v4.8H, v19.8H // multiply accumulate inner loop j = 3, idx = 4..7
> +
> + subs w2, w2, #8 // dstW -= 8
> + sqshrn v0.4H, v0.4S, #7 // shift and clip the 2x16-bit final values
> + sqshrn v1.4H, v5.4S, #7 // shift and clip the 2x16-bit final values
> + st1 {v0.4H, v1.4H}, [x1], #16 // write to dst[idx + 0..7]
> +
> + cbnz w2, 2f // if >0 iterations remain, jump to the wrap up section
> +
> + add sp, sp, #32 // clean up stack
> + ret
> +
> + // finish up when dstW % 8 != 0 or dstW < 16
> +2:
> + // load src
> + ldr w8, [x5], #4 // filterPos[i]
> + add x9, x3, w8, UXTW // calculate the address for src load
> + ld1 {v5.S}[0], [x9] // src[filterPos[i] + 0..3]
> + // load filter
> + ld1 {v6.4H}, [x4], #8 // filter[filterSize * i + 0..3]
> +
> + uxtl v5.8H, v5.8B // unsigned exten long, convert src data to 16-bit
> + smull v0.4S, v5.4H, v6.4H // 4 iterations of src[...] * filter[...]
> + addv s0, v0.4S // add up products of src and filter values
> + sqshrn h0, s0, #7 // shift and clip the 2x16-bit final value
> + st1 {v0.H}[0], [x1], #2 // dst[i] = ...
> + sub w2, w2, #1 // dstW--
> + cbnz w2, 2b
> +
> + add sp, sp, #32 // clean up stack
> + ret
> +endfunc
> diff --git a/libswscale/aarch64/swscale.c b/libswscale/aarch64/swscale.c
> index 09d0a7130e..ab28be4da6 100644
> --- a/libswscale/aarch64/swscale.c
> +++ b/libswscale/aarch64/swscale.c
> @@ -22,25 +22,46 @@
> #include "libswscale/swscale_internal.h"
> #include "libavutil/aarch64/cpu.h"
>
> -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(X8, opt)
> +
> +ALL_SCALE_FUNCS(neon);
>
> void ff_yuv2planeX_8_neon(const int16_t *filter, int filterSize,
> const int16_t **src, uint8_t *dest, int dstW,
> const uint8_t *dither, int offset);
>
> +#define ASSIGN_SCALE_FUNC2(hscalefn, filtersize, opt) do { \
> + if (c->srcBpc == 8 && c->dstBpc <= 14) { \
> + hscalefn = \
> + ff_hscale8to15_ ## filtersize ## _ ## opt; \
> + } \
> +} while (0)
> +
> +#define ASSIGN_SCALE_FUNC(hscalefn, filtersize, opt) \
> + switch (filtersize) { \
> + case 4: ASSIGN_SCALE_FUNC2(hscalefn, 4, opt); break; \
> + default: if (filtersize % 8 == 0) \
> + ASSIGN_SCALE_FUNC2(hscalefn, X8, opt); \
> + break; \
> + }
> +
> av_cold void ff_sws_init_swscale_aarch64(SwsContext *c)
> {
> int cpu_flags = av_get_cpu_flags();
>
> if (have_neon(cpu_flags)) {
> - if (c->srcBpc == 8 && c->dstBpc <= 14 &&
> - (c->hLumFilterSize % 8) == 0 &&
> - (c->hChrFilterSize % 8) == 0)
> - {
> - c->hyScale = c->hcScale = ff_hscale_8_to_15_neon;
> - }
> + ASSIGN_SCALE_FUNC(c->hyScale, c->hLumFilterSize, neon);
> + ASSIGN_SCALE_FUNC(c->hcScale, c->hChrFilterSize, neon);
> if (c->dstBpc == 8) {
> c->yuv2planeX = ff_yuv2planeX_8_neon;
> }
> diff --git a/libswscale/utils.c b/libswscale/utils.c
> index ffa130524a..105781c4f4 100644
> --- a/libswscale/utils.c
> +++ b/libswscale/utils.c
> @@ -1820,7 +1820,7 @@ av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter,
> {
> const int filterAlign = X86_MMX(cpu_flags) ? 4 :
> PPC_ALTIVEC(cpu_flags) ? 8 :
> - have_neon(cpu_flags) ? 8 : 1;
> + have_neon(cpu_flags) ? 4 : 1;
>
> if ((ret = initFilter(&c->hLumFilter, &c->hLumFilterPos,
> &c->hLumFilterSize, c->lumXInc,
> --
> 2.32.0
--
J. Dekker
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