[torqueusers] forcing use of one processor per node?

Steve Young chemadm at hamilton.edu
Wed Apr 16 09:46:13 MDT 2008


Hi John,
	Do you request the amount of memory in your batch scripts? I've  
found that by doing so you shouldn't have to worry about this  
scenario since if the memory isn't available for the second cpu then  
it won't utilize the other half of the node. But if a job comes along  
that can use the rest of the memory and the second cpu you can still  
utilize it.

	The other thing I wonder is, is this an MPI job? I've found MPI can  
be tricky and even though everything appears to work you really have  
to pay attention to what nodes the job really runs on. Torque may  
allocate the job to certain nodes but if MPI doesn't get this  
information from Torque it will pick it's own nodes to run on. I was  
able to solve that with OSC's version of mpiexec which talks directly  
to torque for node allocation.

I just tried a quick test here and I have similar results. I have  
4cpu nodes with 2gb of ram each node. I specify a 4cpu job like you  
did and it stayed on the same node. But when I requested 4gb of ram  
the job went to 4 different nodes.

Anyhow, I'm not sure that answers your question but hopefully gives  
you some more idea's to look at.

-Steve


On Apr 16, 2008, at 11:10 AM, John Young wrote:

> I have a small cluster of dual processor machines.  Normally,
> I would like to keep each processor busy, but sometimes (due
> usually to memory constraints) I would like to force a job
> that I want to run, say, on 4 processors to run on 4 separate
> nodes each using only one processor, rather than on two nodes
> using both processors.
>
> I have tried using things like
>
> #PBS -l nodes=4:ppn=1
>
> and even
>
> #PBS -W x=NACCESSPOLICY:SINGLETASK
>
> but it does not seem to matter.  I always end up using both
> processors on two nodes.  'qstat -a' says that the job is
> using 4 nodes, but it doesn't really...  :-(
>
> Any ideas?
>
> 						JY
> ------------------------------------------------------------
> John E. Young				NASA LaRC B1148/R226
> Analytical Services and Materials, Inc.       (757) 864-8659
> 'All ideas and opinions expressed in this communication are
> those of the author alone and do not necessarily reflect the
> ideas and opinions of anyone else.'
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