So, it appears that for a machine of this type (dual quad core cpu's), this approach would be correct for my tests...

[jpummill@n1 bin]$ more my-hosts
n1 slots=8 max_slots=8

and subsequently, launch two jobs in this configuration...
/home/jpummill/openmpi-1.2.2/bin/mpirun --hostfile my-hosts -np 4 --byslot ./cg.C.4

It appears that this does avoid oversubscribing any particular core as I am not exceeding my core count by running just the two jobs requiring 4 cores each.


Jeff Pummill

George Bosilca wrote:
The cleaner way to define such an environment is by using the max-slots and/or slots options in the hostfile. Here is a FAQ entry about how Open MPI deal with these options (


On Oct 26, 2007, at 10:52 AM, Jeff Pummill wrote:

I am doing some testing on a variety of 8-core nodes in which I just want to execute a couple of executables and have them distributed to the available cores without overlapping. Typically, this would be done with a parameter like -machinefile machines, but I have no idea what names to put into the machines file as this is a single node with two quad core cpu's. As I am launching the jobs sans scheduler, I need to specify what cores to run on I would think to keep from overscheduling some cores while others receive nothing to do at all.

Simple suggestions? Maybe Open MPI takes care of this detail for me?


Jeff Pummill
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