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

[Ronald S. Bultje]

Hi,

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.

Ronald
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