[Q] optimization at Fedora 13

[Q] optimization at Fedora 13

Hi, I am using gfortran for molecular dynamics code and recently installed 11.1 at Fedora 13.

# ifort --version
ifort (IFORT) 11.1 20100414
Copyright (C) 1985-2010 Intel Corporation. All rights reserved.

1. When I installed, it didn't recognize the OS. May intel fortran not suport Fedora 13 fully yet?

2. Anyway, I completed install and compiler seems working - even though sometims there is a problem with "-fast (actually -ipo)",
complaining ld cannot find libraries.

3. I found that the compiler may yield slower result than gfortran. I am using
> gfortran -march=native -ffast-math -funroll-loops -O3
> ifort -O3 -m64 -ipo -no-prec-div
Computer has Intel Xeon CPU W3680 @ 3.33GHz.

Even though performance is very dependent on the code/optimization, the result is quite weird to me. Mostly my code shows 30% better performance with ifort, compared to gfortran. Therefore, I would like to know if there is something I can do for better performance/optimization. Or Fedora13 is not ready for ifort? Any comment will be appreciated.


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For more complete information about compiler optimizations, see our Optimization Notice.

1) Correct, Fedora 13 is not officially supported. It probably will work, however. Read the Release_NotesF.pdf for the list of officially supported linux distributions.

2) if you use -ipo or -fast, you must use xild as your linker, not ld. the object file formats are different for -ipo. In any event, avoid using -fast as it varies by compiler version.

3) -m64 is not necessary or advised. Make sure to 'source /opt/intel/Compiler/11.1/072/bin/ifortvars.sh intel64' to select the Intel 64 compiler and not the 32bit compiler.

You didn't select vectorization with your command line. Try this:

ifort -xhost -O3 -ipo -no-prec-div ....etc...


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