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

[Ronald S. Bultje]

Hi,

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.

Ronald
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