[torqueusers] Computational load on master node?

Garrick Staples garrick at usc.edu
Tue Oct 18 13:20:59 MDT 2005


On Tue, Oct 18, 2005 at 02:34:50PM -0400, Tom Combs alleged:
> Hi,
> 
> I'm in the process of learning about clusters with the intent of 
> building a cluster using LAM/MPI and torque. Assuming that the master 
> node is not listed in the node list, does it carry any of the 
> computational load of jobs that are run through the queue? It is not 

Not generally.  Of course, you could always go out of your way to do it.


> clear to me if the single threaded regions of a job are run on the 
> master node or not. I suspect that one of the computational nodes 
> assigned to a parallel job is assigned as the primary node where all 
> single thread work is done and the other nodes assigned to the job are 
> used for the parallel regions. Can someone clarify this for me?

Your PBS scheduler will assign some nodes to your job.  The first node
in the list is "execution host" or (from TORQUE's perspective) "mother
superior".  TORQUE will run the job script on the exec host.

What your script does is up to you.  It is responsibility of your job to
look at the supplied hostlist for the job as defined in $PBS_NODEFILE
and launch processes on those nodes.

 
> Also, does Torque and LAM/MPI utilize a node comprised of dual 
> processor, dual core Opterons efficiently? Does one configure Torque to 
> see these nodes as containing 4 processors? Does a piece of MPI code 
> actually use both processors in a node or does it assign two separate 
> jobs to the node?

Yes, TORQUE handles multi-proc nodes just fine.

You'll put the number of processors in the server_priv/nodes file for
each node.  In the case of dual-proc, dual-core machines, you'll want to
add "np=4".

-- 
Garrick Staples, Linux/HPCC Administrator
University of Southern California
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