[Ffmpeg-devel] [PATCH] fix mpegaudiodec on ARM and benchmark

[Michael Niedermayer]

Hi

On Thu, Aug 24, 2006 at 12:08:22AM +0200, Aurelien Jacobs wrote:
[...]
> > >              asm("smull %0, %1, %2, %3     \n\t"\
> > > -                "mov   %0, %0,     lsr #%4\n\t"\
> > > -                "add   %1, %0, %1, lsl #%5\n\t"\
> > > -            : "=r"(lo), "=r"(hi)\
> > > +                "mov   %0, %0,     lsr %4\n\t"\
> > > +                "add   %1, %0, %1, lsl %5\n\t"\
> > > +            : "=&r"(lo), "=&r"(hi)\
> > >              : "r"(b), "r"(a), "i"(FRAC_BITS), "i"(32-FRAC_BITS));\
> > >           hi; })
> > >  #   define MUL64(a,b) ((int64_t)(a) * (int64_t)(b))
> > > -#   define MULH(a, b) ({ int lo, hi; asm ("smull %0, %1, %2, %3" : "=r"(lo), "=r"(hi) : "r"(b),"r"(a)); hi; })
> > > +#   define MULH(a, b) ({ int lo, hi; asm ("smull %0, %1, %2, %3" : "=&r"(lo), "=&r"(hi) : "r"(b),"r"(a)); hi; })
> > 
> > i think not all 4 of the & are needed, but iam not sure ...
> 
> If I remove any one of them, I get a load of messages like this one:
> {standard input}: Assembler messages:
> {standard input}:630: rdhi, rdlo and rm must all be different
> Note that I'm cross-compiling with gcc-4.1 if that's relevant.

hmm ok, then they probably are needed, feel free to commit the patch ...

[...]
> Setting -march=armv5te (which is exactly what my Xscale is) is quite
> slower, I don't understand why:
> BENCHMARKs: VC:   0.000s VO:   0.000s A: 206.553s Sys:   0.438s =  206.991s
> BENCHMARK%: VC:  0.0000% VO:  0.0000% A: 99.7882% Sys:  0.2118% = 100.0000%

maybe bugreport to gcc devels?


> 
> 
> Now I also benchmarked libmad. It's still "slightly" faster !
> BENCHMARKs: VC:   0.000s VO:   0.000s A:  54.212s Sys:   0.407s =   54.618s
> BENCHMARK%: VC:  0.0000% VO:  0.0000% A: 99.2554% Sys:  0.7446% = 100.0000%
> 
> Then I benchmarked ffmp3 r6050 (patched) with --disable-libavcodec_mpegaudio_hp
> BENCHMARKs: VC:   0.000s VO:   0.000s A:  78.751s Sys:   0.419s =   79.171s
> BENCHMARK%: VC:  0.0000% VO:  0.0000% A: 99.4702% Sys:  0.5298% = 100.0000%
> Pretty impressive ! Not so far from libmad !

next thing you could try are the different bitstream readers, the default is
probably not good on arm as it does unaligned reads
see the #defines at the top of libavcodec/bitstream.h
note, if anything fails compilation or such please report it ...

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

In the past you could go to a library and read, borrow or copy any book
Today you'd get arrested for mere telling someone where the library is