Subject: mcpu options for AMCC440 with fpu

From: Patrice Bouchand <[email-masked]>
Date: Mon, 19 Feb 2007 09:45:04 +0100 (CET)

Hello,

   I was searching for the best mcpu option for amcc440, compiling and running a small program you can find here: 
http://magnux.free.fr/gcc/mandelbrot.c. My distro is a ppc fedora core 6, and results are obviously the same using DENX4.0.

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

real    1m15.059s
user    1m14.996s
sys     0m0.060s
-bash-3.00# gcc -O2 -mcpu=440 ./mandelbrot.c -o ./mandelbrot && time ./mandelbrot && rm -f ./mandelbrot

real    0m39.606s
user    0m39.552s
sys     0m0.028s
-bash-3.00# gcc -O2 -mcpu=440fp ./mandelbrot.c -o ./mandelbrot && time ./mandelbrot && rm -f ./mandelbrot

real    1m15.016s
user    1m14.988s
sys     0m0.024s
-bash-3.00# gcc -O2 -msoft-float ./mandelbrot.c -o ./mandelbrot && time ./mandelbrot && rm -f ./mandelbrot

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

* I do not explain why not using FPU gives better results ?

* I did also a test with bzip2.c ( http://pag.csail.mit.edu/~smcc/projects/single-file-programs/bzip2.c ).

----------------------
-bash-3.00# gcc -O2 ./bzip2.c -o ./bzip2 && time ./bzip2 ./oggenc.c && ./bzip2 -d ./oggenc.c.bz2 && rm ./bzip2

real    0m18.478s
user    0m18.216s
sys     0m0.152s
-bash-3.00# gcc -O2 -mcpu=440 ./bzip2.c -o ./bzip2 && time ./bzip2 ./oggenc.c && ./bzip2 -d ./oggenc.c.bz2 && rm ./bzip2

real    0m18.786s
user    0m18.544s
sys     0m0.128s
-bash-3.00# gcc -O2 -mcpu=440fp ./bzip2.c -o ./bzip2 && time ./bzip2 ./oggenc.c && ./bzip2 -d ./oggenc.c.bz2 && rm ./bzip2

real    0m18.811s
user    0m18.548s
sys     0m0.144s
-bash-3.00# gcc -O2 -mcpu=G3 ./bzip2.c -o ./bzip2 && time ./bzip2 ./oggenc.c && ./bzip2 -d ./oggenc.c.bz2 && rm ./bzip2

real    0m18.871s
user    0m18.644s
sys     0m0.104s
----------------------

* mcpu option seems to not have any effect ?

*  My third test was to compile and run mplayer.
- With default options (no mcpu specified), my test mpeg was smooth.
- With mcpu=440fp, my test mpeg was not smooth.

 Can anybody bring me some lights about the right gcc mcpu option for amcc440 ?

Best regards,

       Patrice Bouchand

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