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Subject: Re: [OMPI users] How to specify hosts for MPI_Comm_spawn
From: Robert Kubrick (robertkubrick_at_[hidden])
Date: 2008-07-30 10:24:53


Mark, if you can run a server process on the remote machine, you
could send a request from your local MPI app to your server, then use
an Intercomm to link the local process to the new remote process?

On Jul 30, 2008, at 9:55 AM, Mark Borgerding wrote:

> I'm afraid I can't dictate to the customer that they must upgrade.
> The target platform is RHEL 5.2 ( uses openmpi 1.2.6 )
>
> I will try to find some sort of workaround. Any suggestions on how
> to "fake" the functionality of MPI_Comm_spawn are welcome.
>
> To reiterate my needs:
> I am writing a shared object that plugs into an existing framework.
> I do not control how the framework launches its processes (no mpirun).
> I want to start remote processes to crunch the data.
> The shared object marshall the I/O between the framework and the
> remote processes.
>
> -- Mark
>
>
> Ralph Castain wrote:
>> Singleton comm_spawn works fine on the 1.3 release branch - if
>> singleton comm_spawn is critical to your plans, I suggest moving
>> to that version. You can get a pre-release version off of the
>> www.open-mpi.org web site.
>>
>>
>> On Jul 30, 2008, at 6:58 AM, 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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