Hello,

John Hearns via users <users@lists.open-mpi.org> writes:

> Stupid answer from me. If latency/bandwidth numbers are bad then check
> that you are really running over the interface that you think you
> should be. You could be falling back to running over Ethernet.

I'm quite out of my depth here, so all answers are helpful, as I might have
skipped something very obvious.

In order to try and avoid the possibility of falling back to running
over Ethernet, I submitted the job with:

mpirun -n 2 --mca btl ^tcp osu_latency

which gives me the following error:

,----
| At least one pair of MPI processes are unable to reach each other for
| MPI communications.  This means that no Open MPI device has indicated
| that it can be used to communicate between these processes.  This is
| an error; Open MPI requires that all MPI processes be able to reach
| each other.  This error can sometimes be the result of forgetting to
| specify the "self" BTL.
| 
|   Process 1 ([[37380,1],1]) is on host: s01r1b20
|   Process 2 ([[37380,1],0]) is on host: s01r1b19
|   BTLs attempted: self
| 
| Your MPI job is now going to abort; sorry.
`----

This is certainly not happening when I use the "native" OpenMPI,
etc. provided in the cluster. I have not knowingly specified anywhere
not to support "self", so I have no clue what might be going on, as I
assumed that "self" was always built for OpenMPI.

Any hints on what (and where) I should look for?

Many thanks,
-- 
Ángel de Vicente

Tel.: +34 922 605 747
Web.: http://research.iac.es/proyecto/polmag/
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