On Wed, Feb 26, 2003 at 06:51:55PM -0800, Rhett Monteg Hollander wrote:
> Nuno Teixeira wrote:
> >
> > Hi,
> >
> > Just a little question:
> >
> > Does -march=k6-2 implies -m3dnow? Or -march=pentiumpro implies -mmmx?
> Pentium Pro doesn't support MMX; -march=pentiumpro (aka -march=i686) enables
> compiling with main i686 instruction set, no MMX\SSE or whatever.
>
> >
> > I always thought that when I use -march it will enable other
> > porcessor specific optimizations like mmx and 3dnow (if available).
> No way. Besides, only a dozen of open-source UNIX applications can really
> profit from MMX, so it's absurd to use -mmmx for day-by-day use. To be correct,
> MMX is only useful for real-time video\audio processing.
>
> A little example: consider some 16-bit pixel set that you need to increase
> brightness, i.e. to add some value to every pixel. You can load a word into
> integer register, process, and store. You can also load a quadword of four
> 16-bit values into MMX register which is mapped onto FPU register, process them
> at once, and store. Indeed to be faster.
>
> Enabling MMX usually results in about 50% performance increase for true CISC
> processors like P-MMX, and about 20% for PII and up.
>
> ---
> Regards,
> Rhett
>
Hi,
I understand it. Anyway, there is known problems by using -mmmx or
-m3dnow on builworld/buildkernel? Well, I used allways march=pentiumpro
on stable and now pentium2 on current without any problem.
I use some applications like grip, lame, mplayer, etc. Maybe I get some
extra performance running this apps.
Thanks,
Nuno Teixeira
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