Hi,
Miguel Figueiredo Mascarenhas Sousa Filipe wrote:
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?
By default I do not think Open MPI does any process affinity (although I
could be wrong). See this FAQ for information on process affinity:
http://www.open-mpi.org/faq/?category=tuning#paffinity-defs
http://www.open-mpi.org/faq/?category=tuning#using-paffinity
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.
You could put localhost and specify the number of slots in the default
hostfile, or just pass a hostfile containing local host to mpirun.
By default Open MPI will run on the localhost assuming 1 slot if it does
not detect a resource manager or isn't passed a hostfile.
ps.: should I upgrade to latest openMPI to have my problem
"automagically" solved?
I would definitely update to a newer version. The 1.1 series has many
problems.
Hope this helps,
Tim
