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Subject: Re: [OMPI users] jobs with more that 2, 500 processes will not even start
From: Ralph Castain (rhc_at_[hidden])
Date: 2010-12-14 16:10:59


It applies to both. In the rsh/ssh launcher, there is a limit on how many concurrent ssh/rsh sessions we have open at any one time. This is required due to OS limitations. As each daemon completes its launch, it "daemonizes" and closes the ssh/rsh session, thus enabling another daemon to be launched.

We have launched very large clusters with ssh/rsh without problem.

My best guess here is that Lydia has the -do-not-daemonize flag (or mca param) set somewhere, perhaps for debug purposes so that stdout/stderr will be forwarded by ssh/rsh. Unfortunately, that means the session doesn't get closed, and blocks the launch from completing. We are supposed to detect that situation and output an error message before aborting.

However, without more info from her, there is nothing more I can do.

On Dec 14, 2010, at 1:53 PM, Gilbert Grosdidier wrote:

> Bonjour Ralph,
>
> I wonder : is this plm_rsh_num_concurrent parameter standing ONLY for rsh use,
> or for ssh OR rsh, depending on plm_rsh_agent, please ?
>
> Thanks, Best, G.
>
>
> Le 14/12/2010 18:30, Ralph Castain a écrit :
>> That's a big cluster to be starting with rsh! :-)
>>
>> When you say it won't start, do you mean that it hangs? Or does it fail with some error message? How many nodes are involved (this is the important number, not the number of cores)?
>>
>> Also, what version are you using?
>>
>>
>> On Dec 14, 2010, at 9:10 AM, Lydia Heck wrote:
>>
>>> About 9 months ago we had a new installation with a system of 1800 cores and at the time we found that jobs with more than 1028 cores would not start. At the time a colleague found that setting
>>>
>>> OMPI_MCA_plm_rsh_num_concurrent=256
>>>
>>> help with the problem.
>>>
>>> We have now increased our processor count to more than 2700 cores and a job with 2,500 jobs does not start.
>>>
>>> Is there any advice?
>>>
>>> Best wishes,
>>>
>>> Lydia Heck
>>> ------------------------------------------
>>> Dr E L Heck
>>> Senior Computer Manager
>>>
>>> University of Durham Institute for Computational Cosmology
>>> Ogden Centre
>>> Department of Physics South Road
>>>
>>> DURHAM, DH1 3LE United Kingdom
>>>
>>> e-mail: lydia.heck_at_[hidden]
>>>
>>> Tel.: + 44 191 - 334 3628
>>> Fax.: + 44 191 - 334 3645
>>> ___________________________________________
>>> _______________________________________________
>>> users mailing list
>>> users_at_[hidden]
>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
> --
> Cordialement, Gilbert.
>
> --
> *---------------------------------------------------------------------*
> Gilbert Grosdidier Gilbert.Grosdidier_at_[hidden]
> LAL / IN2P3 / CNRS Phone : +33 1 6446 8909
> Faculté des Sciences, Bat. 200 Fax : +33 1 6446 8546
> B.P. 34, F-91898 Orsay Cedex (FRANCE)
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