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Subject: Re: [OMPI users] How to specify hosts for MPI_Comm_spawn
From: Mark Borgerding (markb_at_[hidden])
Date: 2008-07-30 09:12:44

Just to clarify: the test code I wrote does *not* use MPI_Comm_spawn in
the mpirun case. The problem may or may not exist under miprun.

Ralph Castain wrote:
> 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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