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Subject: Re: [OMPI users] Xgrid and choosing agents...
From: Klymak Jody (jklymak_at_[hidden])
Date: 2009-07-11 15:18:10

Hi Vitorio,

Thanks for getting back to me! My hostfile is

xserve01.local max-slots=8
xserve02.local max-slots=8
xserve03.local max-slots=8
xserve04.local max-slots=8

I've now checked, and this seems to work fine just using ssh. i.e. if
I turn off the Xgrid queue manager I can submit jobs manually to the
appropriate nodes using --hosts.

However, I'd really like to use Xgrid as my queue manager as it is
already set up (though I'll happily take hints on how to set up other
queue managers on an OS X cluster).

> So you have 4 nodes each one with 2 processors, each processor 4-
> core - quad-core.
> So you have capacity for 32 process in parallel.

The new Xeon chips designate 2-processes per core, though at a reduced
clock rate. This means that Xgrid believes I have 16 processors/
node. For large jobs I expect that to be useful, but for my more
modest jobs I really only want 8 processes/node.

It appears that the default way xgrid assigns the jobs is to fill all
16 slots on one node before moving to the next. OpenMPI doesn't
appear to look at the hostfile configuration when using Xgrid, so it
makes it hard for me to deprecate this behaviour.

Thanks, Jody

> I think that only using the hostfile is enough is how I use. If you
> to specify a specific host or a different sequence, the mpirun will
> obey the host sequence in your hostfile to start the process, also
> can you put how you configured your host files ? I'm asking this
> because you should have something like:
> # This is an example hostfile. Comments begin with
> # #
> # The following node is a single processor machine:
> # The following node is a dual-processor machine:
> slots=2
> # The following node is a quad-processor machine, and we absolutely
> # want to disallow over-subscribing it:
> slots=4 max-slots=4
> so in your case like mine you should have something like:
> your.hostname.domain slots=8 max-slots=8 # for each node
> I hope this will help you.
> Regards.
> Vitorio.
> Le 09-07-11 à 10:56, Klymak Jody a écrit :
>> Hi all,
>> Sorry in advance if these are naive questions - I'm not experienced
>> in running a grid...
>> I'm using openMPI on 4 duo Quad-core Xeon xserves. The 8 cores
>> mimic 16 cores and show up in xgrid as each agent having 16
>> processors. However, the processing speed goes down as the used
>> processors exceeds 8, so if possible I'd prefer to not have more
>> than 8 processors working on each machine at a time.
>> Unfortunately, if I submit a 16-processor job to xgrid it all goes
>> to "xserve03". Or even worse, it does so if I submit two separate
>> 8-processor jobs. Is there anyway to steer jobs to less-busy agents?
>> I tried making a hostfile and then specifying the host, but I get:
>> /usr/local/openmpi/bin/mpirun -n 8 --hostfile hostfile --host
>> xserve01.local ../build/mitgcmuv
>> Some of the requested hosts are not included in the current
>> allocation for the
>> application:
>> ../build/mitgcmuv
>> The requested hosts were:
>> xserve01.local
>> so I assume --host doesn't work with xgrid?
>> Is a reasonable alternative to simply not use xgrid and rely on ssh?
>> Thanks, Jody
>> --
>> Jody Klymak
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
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