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Subject: Re: [OMPI users] How to specify hosts for MPI_Comm_spawn
From: Ralph Castain (rhc_at_[hidden])
Date: 2008-07-30 08:58:23

As your own tests have shown, it works fine if you just "mpirun -n 1 ./
spawner". It is only singleton comm_spawn that appears to be having a
problem in the latest 1.2 release. So I don't think comm_spawn is
"useless". ;-)

I'm checking this morning to ensure that singletons properly spawns on
other nodes in the 1.3 release. I sincerely doubt we will backport a
fix to 1.2.

On Jul 30, 2008, at 6:49 AM, Mark Borgerding wrote:

> I keep checking my email in hopes that someone will come up with
> something that Matt or I might've missed.
> I'm just having a hard time accepting that something so fundamental
> would be so broken.
> The MPI_Comm_spawn command is essentially useless without the
> ability to spawn processes on other nodes.
> If this is true, then my personal scorecard reads:
> # Days spent using openmpi: 4 (off and on)
> # identified bugs in openmpi :2
> # useful programs built: 0
> Please prove me wrong. I'm eager to be shown my ignorance -- to
> find out where I've been stupid and what documentation I should've
> read.
> Matt Hughes wrote:
>> I've found that I always have to use mpirun to start my spawner
>> process, due to the exact problem you are having: the need to give
>> OMPI a hosts file! It seems the singleton functionality is lacking
>> somehow... it won't allow you to spawn on arbitrary hosts. I have
>> not
>> tested if this is fixed in the 1.3 series.
>> Try
>> mpiexec -np 1 -H op2-1,op2-2 spawner op2-2
>> mpiexec should start the first process on op2-1, and the spawn call
>> should start the second on op2-2. If you don't use the Info object
>> to
>> set the hostname specifically, then on 1.2.x it will automatically
>> start on op2-2. With 1.3, the spawn call will start processes
>> starting with the first item in the host list.
>> mch
> [snip]
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