alan at redhat.com
Mon Jan 14 20:38:01 UTC 2008
On Mon, Jan 14, 2008 at 02:14:02PM -0600, Callum Lerwick wrote:
> using OpenJPEG's MJ2 tools, I encode the speedway example using
> "frames_to_mj2 -i Speedway.yuv -o Speedway.mj2 -I 1", then decode it.
Which is about the most extreme case you will find.
> So it is 0.54% *slower* when compiled for i586, which is unexpected and
> strange, but such is gcc. I wouldn't expect much of a speed difference
> compiling for i586, there was no major additions to the instruction set,
> and we're already scheduling for modern processors.
586 has completely different scheduling pipelines wiht complex rules
> Not quite "three times" faster, but 3.26% faster with i686. A major
> addition to the i686 architecture was cmov, and gcc is actually very
Current CPUs cmov is generally a lose.
> both i386 and i686 versions. glibc and openssl already do this. Off the
> top of my head, this would include Mesa, I know for a fact the majority
Mesa already internally uses things like 3DNow. The Mesa folks would
I'm sure welcome more optimised paths and cpu tuned variants.
> all the help it can get. Not that the MPEG4 codecs are in Fedora
MPEG4 is dominated by memory bandwidth so cache size is critical and
FSB, not compiler options.
Memory actually dominates most things today - and -Os is often the macro
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