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Subject: Re: [OMPI devel] Can I have the same node specified multiple times in a host file?
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-09-04 16:37:48


You need to use the sequential mapper instead of the default round-
robin one. Set -mca rmaps seq on your cmd line. We will then assign
ranks to nodes in sequential order based on the hostfile entries.

On Sep 4, 2009, at 11:25 AM, Karl, Robert (RKARL) wrote:

> I am attempting force certain processes to run on specific nodes due
> to the
> I/O cards that are attached to the specific CPU motherboards (not
> all boards
> have the same I/O cards). I am using the -bynode and --hostname
> options to
> specify the nodes that I want the processes to run on. There are 4
> processors (nodes) per motherboard. I would like to be able to
> change the
> motherboard each processor executes on simply by editing the host
> file to
> change the ordering of the nodes in the host file.
>
> For example:
> I want process 0, 1 and 4 to run on node0 and process 2 and 3 to run
> on
> node1.
>
> shell$ cat my-hosts
> node0 slots=4
> node0 slots=4
> node1 slots=4
> node1 slots=4
> node0 slots=4
>
> shell$ mpirun --hostfile my-hosts -np 5 --bynode
>
> What I end up with is process 1& 3 running on node0 and process
> 0,2,4 running
> on
> node1. I suspect that MPI does not like having the same node
> multiple times
> in the host file. It appears that only the last 2 entries of the
> host file
> are being used and then the processes are being assigned in a round
> robin
> fashion by node. Is what I'm doing legal? Any suggestions to
> achieve the
> intended results (which is to be able to force an arbitary process
> to run on
> an arbitary node)?
>
> Thanks,
>
> Bob
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