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From: Miguel Figueiredo Mascarenhas Sousa Filipe (miguel.filipe_at_[hidden])
Date: 2007-10-03 09:52:05

Hi there,

I have a 2-cpu system (linux/x86-64), running openmpi-1.1. I do not
specify a hostfile.
Lately I'm having performance problems when running my mpi-app this way:

mpiexec -n 2 ./mpi-app config.ini

Both mpi-app processes are running on cpu0, leaving cpu1 idle.

After reading the mpirun manpage, it seems that openmpi bind tasks to
cpus in a round-robin way, meaning that this should not happen.
But given my problem, I assume that it's not detecting this is a 2-way
smp system, (assuming a UP system) and binding both tasks to cpu0..

Is this correct?

The openmpi-default-hostfile says I should not specify localhost in
there.. and let the job dispatcher/rca "detect" the single-node setup.

Where should I define/configure system wide, that this is a
single-node, 2-slot system?
I would like to avoid making the system users be obliged to pass a
hostfile to mpirun/mpiexec. I simply want mpiexec -n N ./mpi-task to
do the propper job of _really_ spreading the processes evenly between
all the system's CPUs.

Best regards, waiting for your answer.

ps.: should I upgrade to latest openMPI to have my problem
"automagically" solved?

Miguel Sousa Filipe