OpenMPI won't work properly with Lammps (Multitask fails)


I have lammps, and OpenMPI 1.8.1 installed on my 8 core machine (CentOS 6.5, AMD). When I run one job OpenMPI works fine, but wehn I run more than one job everything slows down greatly.

For example, I run a job on all 8 cores and it works because according to System Monitor all cores are %100 in use. But, if I run one job on 4 cores and another job on another 4 cores, when I look at the System Monitor it says that just 4 cores are %100 in use, and everything is super slow.

BTW, the same thing happens with my other machine that has 24 cores (CentOS 6.5, AMD)

Has anybody experienced an issue like that?

This is an openmpi issue. Very likely due to processor affinity. Please reread the openmpi docs, study the openmpi webpage and post to there mailinglist if you continue to have problems.