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I'm doing a Cactus run which I've compiled with OpenMp support on my linux machine, and looking at the performance in the routine in which I explicitly added a "parallel do" directive. When I change the environment variable OMP_NUM_THREADS to anything larger than 1, it actually takes LONGER than the 1-thread run. I have *24* processors on my machine. It runs fine on my mac, but not my linux machine.
Does anyone have a suggestion?
I notice my version of gcc doesn't have --enable-openmp (see below)... but then the worst it should do is not have any effect when OMP_NUM_THREADS is set to anything.
Thanks! Scott
mpicc -v
Using built-in specs. Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.5-8' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --with-arch-32=i586 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.4.5 (Debian 4.4.5-8)
libgomp is version 4.4.5-8 ... but there is no lib64gomp. Odd. I'm using Debian squeeze which supposedly contains lib64gomp.
- -- Scott H. Hawley, Ph.D. Asst. Prof. of Physics Chemistry & Physics Dept Office: Hitch 100D Belmont University Tel: +1-615-460-6206 Nashville, TN 37212 USA Fax: +1-615-460-5458 PGP Key at http://sks-keyservers.net