OpenMP+gfortran performance extremely variable between dlopen's of libgomp

Anand Patil
Tue Jan 15 02:33:00 GMT 2008

Hi all,

As in my last help request, I'm using gfortran 4.2.1 from Ubuntu
Gutsy's apt-get, with the patch from bug 28482 ( ) applied so that I
can dlopen libgomp. I find that the performance of my subroutines
varies greatly if I reload libgomp, but if I rerun the subroutines
several times for the same load of libgomp performance is fairly
constant. Other information that may be relevant:

- The number of threads stays the same (I have OMP_DYNAMIC=False).
- The relative speedup from OpenMP (wall time / CPU time) stays
relatively constant.

I don't even know where to start looking for the source of this
behavior. Any tips?

Anand Patil

More information about the Gcc-help mailing list