I have installed OpenMPI on a cluster consisting of ~30 nodes with 16 Xeon cores each. NFS is set up and working. For testing I have installed locally with
./configure --prefix=/home_dir/openmpi-1.4.3_installation/; make all install
everything smooth so far.
When I run a parallel program with
/home_dir/openmpi-1.4.3_installation/bin/mpirun -n 2 ./my_parprog
everything scales perfectly up to -n 16. When I go to -n 32, the execution time is the same as with -n 16.
/home_dir/openmpi-1.4.3_installation/bin/mpirun -n 32 hostname
returns 32 times the same node.
The program is fine (runs since years on several machines) and another mpi installation scales well, so the cluster should be ok as well.
What did I do wrong???
Thanks for any hint!
Dr. Steffen Brinkmann
High Performance Computing Center Stuttgart (HLRS)
D - 70569 Stuttgart
Phone: ++49(0)711 / 685-64548
Fax: ++49(0)711 / 685-65832