[x265] [PATCH] dct: unroll for 30% speedup on Apple Silicon

[chen]

In this case, I more like keep current code no change.

The performance strong depends to compiler, and not so much benefits, we may optimize by asm future.

 2024-11-24 23:54:48，"Ganesh Ajjanagadde" <gajjanag2 at gmail.com> 

Right, this only affects the dct32 case. Others are unaffected and change is within noise for them.


On Sat, Nov 23, 2024 at 9:57 PM chen <chenm003 at 163.com> wrote:


Looks for dct32x32 and idct4x4 only, other size are similar or worse?




At 2024-11-24 12:34:48, gajjanag2 at gmail.com wrote:
>From: Ganesh Ajjanagadde <gajjanag at alum.mit.edu>
>
>Apple silicon has 4 128 bit NEON execution units and benefits from unrolling.
>
>From ./TestBench on an M4 Mac Mini,
>
>before:
>dct8x8		 | 	2.32x | 	 205.12   | 	 476.62
>dct16x16	 | 	2.02x | 	 801.20   | 	 1619.62
>dct32x32	 | 	3.47x | 	 7566.39  | 	 26275.65
>idct4x4		 | 	0.90x | 	 175.80   | 	 157.90
>idct16x16	 | 	2.05x | 	 863.30   | 	 1771.80
>idct32x32	 | 	1.79x | 	 6344.33  | 	 11351.99
>
>after:
>dct8x8		 | 	2.33x | 	 204.72   | 	 476.53
>dct16x16	 | 	2.04x | 	 802.16   | 	 1637.39
>dct32x32	 | 	4.96x | 	 5181.02  | 	 25700.34
>idct4x4		 | 	1.08x | 	 162.09   | 	 174.40
>idct16x16	 | 	1.95x | 	 910.01   | 	 1771.61
>idct32x32	 | 	1.75x | 	 6350.72  | 	 11143.71
>
>~2% end to end encoding speedup
>---
> source/common/aarch64/dct-prim.cpp | 2 ++
> 1 file changed, 2 insertions(+)
>
>diff --git a/source/common/aarch64/dct-prim.cpp b/source/common/aarch64/dct-prim.cpp
>index 8b523ceb0..e6ee7005b 100644
>--- a/source/common/aarch64/dct-prim.cpp
>+++ b/source/common/aarch64/dct-prim.cpp
>@@ -435,6 +435,7 @@ static inline void partialButterfly32_neon(const int16_t *src, int16_t *dst)
>         for (int i = 0; i < line; i += 4)
>         {
>             int32x4_t t[4];
>+X265_PRAGMA_UNROLL(4)
>             for (int j = 0; j < 4; ++j) {
>                 t[j] = vmull_s16(c0, vget_low_s16(O[i + j][0]));
>                 t[j] = vmlal_s16(t[j], c1, vget_high_s16(O[i + j][0]));
>@@ -461,6 +462,7 @@ static inline void partialButterfly32_neon(const int16_t *src, int16_t *dst)
>         for (int i = 0; i < line; i += 4)
>         {
>             int32x4_t t[4];
>+X265_PRAGMA_UNROLL(4)
>             for (int j = 0; j < 4; ++j) {
>                 t[j] = vmulq_s32(c0, EO[i + j][0]);
>                 t[j] = vmlaq_s32(t[j], c1, EO[i + j][1]);
>-- 
>2.39.5 (Apple Git-154)
>
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