[FFmpeg-devel] [HACK] 50% faster H.264 decoding

[Ronald S. Bultje]

Hi,

On Thu, Aug 19, 2010 at 4:46 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
> On Thu, Aug 19, 2010 at 4:34 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>> On Thu, Aug 19, 2010 at 12:55 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>>> On Thu, Aug 19, 2010 at 9:56 AM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>>>> On Wed, Aug 18, 2010 at 6:44 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>>>>> On Wed, Aug 18, 2010 at 6:28 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>>>>>> On Wed, Aug 18, 2010 at 12:42:11PM -0400, Ronald S. Bultje wrote:
>>>>>>> On Tue, Aug 17, 2010 at 1:35 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>>>>>>> > On Tue, Aug 17, 2010 at 11:01:03AM -0400, Ronald S. Bultje wrote:
>>>>>>> >> On Mon, Aug 16, 2010 at 6:40 PM, Jason Garrett-Glaser
>>>>>>> >> <darkshikari at gmail.com> wrote:
>>>>>>> >> > On Mon, Aug 16, 2010 at 3:35 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>>>>>>> >> >> Hi,
>>>>>>> >> >>
>>>>>>> >> >> On Wed, Aug 11, 2010 at 5:32 PM, Jason Garrett-Glaser
>>>>>>> >> >> <darkshikari at gmail.com> wrote:
>>>>>>> >> >>> 13. Use MPEG-2 MC for chroma MC, since we know that MVs are
>>>>>>> >> >>> fullpel-only. ?Simplify edge emulation stuff accordingly too.
>>>>>>> >> >>
>>>>>>> >> >> Does h264 chroma subpel actually use a memcpy shortcut if it's
>>>>>>> >> >> fullpel? I don't remember exactly, but I don't think it has such a
>>>>>>> >> >> shortcut for chroma, only for luma.
>>>>>>> >> >
>>>>>>> >> > It doesn't. ?It should at least have a shortcut for the 0,0 motion
>>>>>>> >> > vector because its very high probability (relative to other fullpel
>>>>>>> >> > motion vectors that result in no chroma interpolation). ?For other
>>>>>>> >> > cases, it might or might not be worthwhile to add a branch in the asm
>>>>>>> >> > to the 1D-only case.
>>>>>>> >>
>>>>>>> >> Attached sets up framework for that. The [0] functions can be copied
>>>>>>> >> straight from VP8 (they are pixel_copy functions, with very fast
>>>>>>> >> aligned implementations for all relevant archs) and others, and should
>>>>>>> >> make VC-1, RV3/4, h264, H264/MPEG etc. significantly faster for the
>>>>>>> >> MVxy==0 case. The [1]/[2] functions are probably going to be faster as
>>>>>>> >> well but that would need some testing to see how big the effect is.
>>>>>>> >> [3] is the function as-is now, which should obviously stay the way it
>>>>>>> >> is.
>>>>>>> >>
>>>>>>> >> Michael, OK to apply this? It's mostly just changing all kind of files
>>>>>>> >
>>>>>>> > if its not slower ...
>>>>>>>
>>>>>>> Same speed. Attached is an updated version that fixes a bug in one of
>>>>>>> the fate samples where mx gets changed and thus we called the wrong
>>>>>>> version.
>>>>>>>
>>>>>>> I've tested this version with a semi-finished patch that splits up the
>>>>>>> h264 chroma MC functions (particularly the mc8 ones) into smaller
>>>>>>> ones, thus having cleaner (and unbranched) handling of mx==0/my==0.
>>>>>>> This will remove most (if not all) of the branching, which might give
>>>>>>> a minor speedup, and also removes a little duplicate code (in the
>>>>>>> binary, not source), e.g. the fullpel handling between
>>>>>>> mmx/3dnow/mmx2/ssse3 rv40/h264/vc1 mc8 is identical (it's all
>>>>>>> put_pixels8_mmx) and only needs a single function. I'm only doing this
>>>>>>> for the C and x86 ones because I can't test any of the others.
>>>>>>>
>>>>>>> After that's done, I plan to do a third patch which will add fullpel
>>>>>>> or 1D-filter versions for mc4/mc2 as well, which should actually
>>>>>>> provide a speedup for code on our desktops, as we saw for Jason's
>>>>>>> hackpatch.
>>>>>>>
>>>>>>> Ronald
>>>>>>
>>>>>>> ?arm/dsputil_init_neon.c | ? 32 ++++++++++---
>>>>>>> ?cavs.c ? ? ? ? ? ? ? ? ?| ? 13 ++---
>>>>>>> ?dsputil.c ? ? ? ? ? ? ? | ? 40 +++++++++++++---
>>>>>>> ?dsputil.h ? ? ? ? ? ? ? | ? 12 ++--
>>>>>>> ?h264.c ? ? ? ? ? ? ? ? ?| ? 24 +++++----
>>>>>>> ?mpegvideo.c ? ? ? ? ? ? | ? 28 ++++++-----
>>>>>>> ?ppc/h264_altivec.c ? ? ?| ? 20 ++++++--
>>>>>>> ?rv34.c ? ? ? ? ? ? ? ? ?| ? ?9 ++-
>>>>>>> ?rv40dsp.c ? ? ? ? ? ? ? | ? 20 ++++++--
>>>>>>> ?sh4/dsputil_align.c ? ? | ? 30 +++++++++---
>>>>>>> ?vc1dec.c ? ? ? ? ? ? ? ?| ? 33 +++++++------
>>>>>>> ?vp6.c ? ? ? ? ? ? ? ? ? | ? ?6 +-
>>>>>>> ?x86/dsputil_mmx.c ? ? ? | ?118 +++++++++++++++++++++++++++++++++++++-----------
>>>>>>> ?13 files changed, 272 insertions(+), 113 deletions(-)
>>>>>>> 183027123a1213b2e037504a01d87c9c0678c1db ?h264-chroma-mvzero-shortcut.patch
>>>>>>
>>>>>> no objections
>>>>>
>>>>> Attached are the follow-up patches, C-only for now (still working on the asm).
>>>>>
>>>>> Patch #1 splits the H264 macro function creation macros into two, and
>>>>> makes vc1_no_rnd use this macro instead of re-doing its own version of
>>>>> it. Patch somehow thinks I changed mc2 into mc8, mc4 into mc2 and mc8
>>>>> into mc4, rather than seeing I moved mc8 up from below, but the patch
>>>>> should be readable nevertheless.
>>>>>
>>>>> Patch #2 then splits the C functions into 3: one each for x=0 or y=0,
>>>>> and the remaining one for 2D bilinear filtering. It also adds one for
>>>>> the case where x=0 AND y=0 (direct copy). Make fate has no objections.
>>>>> There is no speed change for 1D/2D. The direct copy would be expected
>>>>> to be faster but I didn't test because the C code isn't that relevant.
>>>>> I can test if you prefer, but I'd rather focus on the asm functions
>>>>> and make sure every change there is speed-tested. If you want, I can
>>>>> move the adding of the direct copy functions to a separate patch, but
>>>>> I didn't think that was necessary.
>>>>>
>>>>> I will do similar splits to the asm code
>>>> [..]
>>>>
>>>> And these can be found in attached. Iv'e checked make fate for MMX,
>>>> MMX2 and SSSE3 and all is identical. I will do some basic performance
>>>> checks to make sure I didn't screw up anything, but speed should be
>>>> identical except maybe for MMX avg_mc8 for x=0&&y=0, which is added by
>>>> this patch (it was pretty much a one-liner). This is generally not
>>>> used since MMX2/3DNOW versions are available also. If wanted, I can
>>>> separate this or remove it.
>>>>
>>>> Next step is to actually implement new functions for 1D/no-filter
>>>> mc4/mc2 which leads to the actually wanted speedup.
>>>
>>> Example of such an optimization attached, so we can start applying
>>> this whole thing (now that I'm showing an actual improvement in
>>> performance :-) ).
>>>
>>> START/STOP_TIMER around chroma_op[]() in h264.c, measuring only the
>>> case where mx=0, my=0 and chroma_function_index=1 (local hack). CPU is
>>> Intel Core i7 (Macbook Pro, OSX 10.6.4). GCC:
>>> i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664).
>>> Sample: /Users/ronaldbultje/Movies/fate-suite/h264-conformance/MR3_TANDBERG_B.264
>>>
>>> after:
>>> 1925 dezicycles in w=4,mx=0,my=0, 2 runs, 0 skips
>>> 2075 dezicycles in w=4,mx=0,my=0, 4 runs, 0 skips
>>> 2445 dezicycles in w=4,mx=0,my=0, 8 runs, 0 skips
>>> 1903 dezicycles in w=4,mx=0,my=0, 16 runs, 0 skips
>>> 1792 dezicycles in w=4,mx=0,my=0, 32 runs, 0 skips
>>> 1609 dezicycles in w=4,mx=0,my=0, 64 runs, 0 skips
>>>
>>> before (here it would use the 2D filter ssse3 code):
>>> 2990 dezicycles in w=4,mx=0,my=0, 2 runs, 0 skips
>>> 2850 dezicycles in w=4,mx=0,my=0, 4 runs, 0 skips
>>> 2917 dezicycles in w=4,mx=0,my=0, 8 runs, 0 skips
>>> 2623 dezicycles in w=4,mx=0,my=0, 16 runs, 0 skips
>>> 2505 dezicycles in w=4,mx=0,my=0, 32 runs, 0 skips
>>> 2518 dezicycles in w=4,mx=0,my=0, 64 runs, 0 skips
>>>
>>> C-only (the version after my patches applied, so the 32-bit direct
>>> read/write loop):
>>> 5230 dezicycles in w=4,mx=0,my=0, 2 runs, 0 skips
>>> 5215 dezicycles in w=4,mx=0,my=0, 4 runs, 0 skips
>>> 5755 dezicycles in w=4,mx=0,my=0, 8 runs, 0 skips
>>> 4255 dezicycles in w=4,mx=0,my=0, 16 runs, 0 skips
>>> 3819 dezicycles in w=4,mx=0,my=0, 32 runs, 0 skips
>>> 3772 dezicycles in w=4,mx=0,my=0, 64 runs, 0 skips
>>
>> By popular request, here's one that adds the new code to
>> dsputil_yasm.asm instead of dsputil_mmx.c. Now I can actually read my
>> own code, too. make fate-h264 didn't complain about this change.
>
> Now with actual new patch. Thanks Alex for noticing.

And same patch for mc2,x=0,y=0.

after (direct copy mc2):
2178 dezicycles in w=2,mx=0,my=0, 512 runs, 0 skips
2096 dezicycles in w=2,mx=0,my=0, 1023 runs, 1 skips
2109 dezicycles in w=2,mx=0,my=0, 2047 runs, 1 skips

before (ssse3 2D filter):
2493 dezicycles in w=2,mx=0,my=0, 511 runs, 1 skips
2469 dezicycles in w=2,mx=0,my=0, 1022 runs, 2 skips
2477 dezicycles in w=2,mx=0,my=0, 2046 runs, 2 skips

c (note how this is actually faster than ssse3 2D filter):
2329 dezicycles in w=2,mx=0,my=0, 512 runs, 0 skips
2354 dezicycles in w=2,mx=0,my=0, 1024 runs, 0 skips
2334 dezicycles in w=2,mx=0,my=0, 2048 runs, 0 skips

Ronald
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