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From: Brock Palen (brockp_at_[hidden])
Date: 2006-11-22 00:09:07


Feel free to correct me if im wrong.

OMPI assumes you have a fast network and checks for them. If they
are not found it falls back to tcp.

So if you leave out the --mca etc etc.... It should use the mx if
its available. Im not sure how MX responds if one of the hosts does
not have a working card (not activated) because the mpi job will
still run. Just not using MX to that host. All other hosts will us MX.

If openmpi sees that a node has more than one cpu (SMP) It will use
the sm (shared mem) method to communicate over the mx. and if a
proc sends to its self, the self method is used. So its like a
priority order.

I know there is a way (its in the archives) to see the priority on
how OMPI choses what method to use. and uses the highest priority
that will allow the communication to complete.

I know there is also some magic being working on/implemented. That
will stripe over multiple networks for large messages when more
bandwidth is needed. I dont know if OMPI will have this ability or
not. Someone else can chime in on that.

Brock Palen
Center for Advanced Computing
brockp_at_[hidden]
(734)936-1985

On Nov 21, 2006, at 11:28 PM, Iannetti, Anthony C. ((GRC-RTB0)) wrote:

> Dear OpenMPI List:
>
>
>
> From looking at a recent thread, I see an mpirun command with
> shared memory and mx:
>
>
>
> mpirun –mca btl mx,sm,self –np 2 pi3f90.x
>
>
>
> This works. I may have forgot to mention it, but I am using
> 1.1.2. I see there is an –mca mtl in version 1.2b1 . I do not
> think this exists in 1.1.2.
>
> Still, I would like to know what –mca is given automatically.
>
>
>
> Thanks,
>
> Tony
>
>
>
>
>
>
>
> Anthony C. Iannetti, P.E.
>
> NASA Glenn Research Center
>
> Propulsion Systems Division, Combustion Branch
>
> 21000 Brookpark Road, MS 5-10
>
> Cleveland, OH 44135
>
> phone: (216)433-5586
>
> email: Anthony.C.Iannetti_at_[hidden]
>
>
>
> Please note: All opinions expressed in this message are my own and
> NOT of NASA. Only the NASA Administrator can speak on behalf of NASA.
>
>
>
> From: Iannetti, Anthony C. (GRC-RTB0)
> Sent: Tuesday, November 21, 2006 8:39 PM
> To: 'users_at_[hidden]'
> Subject: MX performance problem on two processor nodes
>
>
>
> Dear OpenMPI List:
>
>
>
> I am running the Myrinet MX btl with OpenMPI on MacOSX
> 10.4. I am running into a problem. When I run on one processor
> per node, OpenMPI runs just fine. When I run on two processors
> per node (slots=2), it seems to take forever (something is hanging).
>
>
>
> Here is the command:
>
> mpirun –mca btl mx,self –np 2 pi3f90.x
>
>
>
> However, if I give the command:
>
> mpirun –np 2 pi3f90.x
>
>
>
> The process runs normally. But, I do not know if it is using the
> Myrinet network. Is there a way to diagnose this problem. mpirun –
> v and –d do not seem to indicate which mca is actually being used.
>
>
>
> Thanks,
>
> Tony
>
>
>
> Anthony C. Iannetti, P.E.
>
> NASA Glenn Research Center
>
> Propulsion Systems Division, Combustion Branch
>
> 21000 Brookpark Road, MS 5-10
>
> Cleveland, OH 44135
>
> phone: (216)433-5586
>
> email: Anthony.C.Iannetti_at_[hidden]
>
>
>
> Please note: All opinions expressed in this message are my own and
> NOT of NASA. Only the NASA Administrator can speak on behalf of NASA.
>
>
>
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