Best mcpu option for amcc440 with fpu ?

Best mcpu option for amcc440 with fpu ?

[Patrice Bouchand]

Hello,

   I'm having trouble trying to find the best
compiling
 option for amcc440 with fpu. I'm using a genuine 
fedora core 6 ppc distro (gcc4.1.1). It seems that 
using mcpu=440 gives better results than -mcpu=440fp, 
even with floating point code ? What could be wrong on

my platform to give such a result ?


The test :
mandelbrot.c is available here:
http://magnux.free.fr/gcc/mandelbrot.c

--------------------
-bash-3.00# gcc -O2 -mcpu=440fp ./mandelbrot.c -o
./mandelbrot && time ./mandelbrot 

real    1m15.016s
user    1m14.988s
sys     0m0.024s

-bash-3.00# gcc -O2 -mcpu=440 ./mandelbrot.c -o
./mandelbrot && time ./mandelbrot

real    0m39.606s
user    0m39.552s
sys     0m0.028s

-bash-3.00# gcc -O2 -msoft-float ./mandelbrot.c -o
./mandelbrot && time ./mandelbrot

real    0m39.577s
user    0m39.544s
sys     0m0.032s

-bash-3.00# gcc -O2 ./mandelbrot.c -o ./mandelbrot &&
time ./mandelbrot

real    1m15.059s
user    1m14.996s
sys     0m0.060s



	

	
		
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Re: Best mcpu option for amcc440 with fpu ?

[Segher Boessenkool]

>    I'm having trouble trying to find the best
> compiling
>  option for amcc440 with fpu. I'm using a genuine
> fedora core 6 ppc distro (gcc4.1.1). It seems that
> using mcpu=440 gives better results than -mcpu=440fp,
> even with floating point code ? What could be wrong on
>
> my platform to give such a result ?

Dunno.  You need to hunt down more details first:

-- Run a profiler (oprofile, gprof) to pinpoint one
specific (preferably smallish) piece of code that has
a huge slowdown;
-- Look at the generated assembler code for that routine
to see what's up;
-- Try to figure out why that happened, or report back
here.


Segher

Re: Best mcpu option for amcc440 with fpu ?

[Patrice Bouchand]

   My program was running faster using mcpu=440 but was not giving the
awaited results (I should add a display sooner...). I was linking a
program build with soft-float setting against libraries using hard-float
setting. 

   Sorry for the noise and thanks for your time.

       Patrice 


Le vendredi 23 février 2007 à 14:16 +0100, Segher Boessenkool a écrit :
> >    I'm having trouble trying to find the best
> > compiling
> >  option for amcc440 with fpu. I'm using a genuine
> > fedora core 6 ppc distro (gcc4.1.1). It seems that
> > using mcpu=440 gives better results than -mcpu=440fp,
> > even with floating point code ? What could be wrong on
> >
> > my platform to give such a result ?
> 
> Dunno.  You need to hunt down more details first:
> 
> -- Run a profiler (oprofile, gprof) to pinpoint one
> specific (preferably smallish) piece of code that has
> a huge slowdown;
> -- Look at the generated assembler code for that routine
> to see what's up;
> -- Try to figure out why that happened, or report back
> here.
> 
> 
> Segher
>