[FFmpeg-devel] [PATCH 5/5] avcodec/h264: add avx 8-bit h264_idct_dc_add
jdarnley at obe.tv
Thu Apr 6 19:01:54 EEST 2017
On 2017-04-05 06:05, James Almer wrote:
> On 4/4/2017 10:53 PM, James Darnley wrote:
>> - 1.02x faster (405±0.7 vs. 397±0.8 decicycles) compared with mmxext
>> - 1.06x faster (498±1.8 vs. 470±1.3 decicycles) compared with mmxext
>> libavcodec/x86/h264_idct.asm | 20 ++++++++++++++++++++
>> libavcodec/x86/h264dsp_init.c | 2 ++
>> 2 files changed, 22 insertions(+)
>> diff --git a/libavcodec/x86/h264_idct.asm b/libavcodec/x86/h264_idct.asm
>> index 24fb4d2..7fd57d3 100644
>> --- a/libavcodec/x86/h264_idct.asm
>> +++ b/libavcodec/x86/h264_idct.asm
>> @@ -1158,7 +1158,27 @@ INIT_XMM avx
>> movd [%7+%8], %4
>> +%macro DC_ADD_INIT 1
>> + add %1d, 32
>> + sar %1d, 6
>> + movd m0, %1d
>> + SPLATW m0, m0, 0
> Considering DC_ADD_MMXEXT_OP works with dwords, a single pshuflw should be
> enough. This macro calls two instructions to fill the entire XMM register,
> and there's no need for that.
Noted, I made that change butit doesn't seemto change much in terms of
> You could for that matter try to optimize DC_ADD_MMXEXT_OP a bit, combining
> said dwords with punpk* into fewer registers to reduce the amount of padd*
> and psub* needed afterwards. See ADD_RES_MMX_4_8 in hevc_add_res.asm
Noted. Maybe in the future.
> And again, SSE2 first, AVX only if measurably faster. But since you're not
> making use of the wider XMM regs here at all, the only chips that will see
> any real speed up are those slow in mmx (like Skylake seems to be).
Yorkfield gets no benefit from sse2 (575±0.4 vs. 574±0.3 decicycles).
Haswell gets most of its benefit from sse2 (404±0.6 vs. 390±0.3 vs.
Skylake-U gets all of its speedup from sse2 (533±3.0 vs 488±2.0 vs 497±1.4).
Nehalem and 64-bit also gets no benefit from sse2.
Again: SSE2 yay or nay? Maybe I should just drop this; I'm not sure 5
cycles is worth it.
(I will now go and modify my script to divide the recorded decicycle
count by 10.)
>> +cglobal h264_idct_dc_add_8, 3, 4, 0, dst_, block_, stride_
Fixed this bug.
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