[FFmpeg-devel] [RFC] optimize ff_emulated_edge_mc

[Michael Niedermayer]

On Wed, Dec 29, 2010 at 10:03:04PM -0500, Ronald S. Bultje wrote:
> Hi,
> 
> On Wed, Dec 29, 2010 at 8:06 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
> > emu_edge_mc looks optimizable and shows up in my profilings. A simple
> > loop->memcpy makes things a lot faster already (see attached):
> [..]
> > after
> [..]
> > 6165 dezicycles in ff_emulated_edge_mc, 1048040 runs, 536 skips
> > 6115 dezicycles in ff_emulated_edge_mc, 1048044 runs, 532 skips
> > 6087 dezicycles in ff_emulated_edge_mc, 1048158 runs, 418 skips
> >
> > before
> [..]
> > 9104 dezicycles in ff_emulated_edge_mc, 1047805 runs, 771 skips
> > 9131 dezicycles in ff_emulated_edge_mc, 1047866 runs, 710 skips
> > 9097 dezicycles in ff_emulated_edge_mc, 1047874 runs, 702 skips
> [..]
> 
> Another few more changes attached, doing memcpy() on top/bottom edge
> brings it to 540 cycles:
> 
> 5414 dezicycles in ff_emulated_edge_mc, 1048331 runs, 245 skips
> 
> and then reordering the left/right edge loop a little brings it to 520:
> 
> 5186 dezicycles in ff_emulated_edge_mc, 1048288 runs, 288 skips
> 
> I'm too lazy to run this multiple times.
> 
> For the left/right edge fills, I tried using memset(), but that slows
> it down considerably, it appears it doesn't inline it. Jason said he
> saw the same on some compilers withthe memcpy() trick. Which makes me
> think, maybe we can emulate the inline memset() trick with some more
> elaborate C code? What I'm thinking is basically edge_val *=
> 0x01010101U; while (to_write >= 4) write(edge_val); if (to_write&2)
> write(edge_val); if (to_write & 1) write(edge_val); or so. Also, since
> most time is spent in copying the blocks quite literally, the main
> copy block could certainly use some optimizations, especially since
> width is generally something like 16...
> 
> Ronald

>  dsputil.c |   22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 6b5be1a69247178dd53af1f622a49750d231045d  emu_edge_mc.patch

feel free to commit whatever makes ff_emulated_edge_mc() faster

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
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even the very wise cannot see all ends. -- Gandalf
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