[torqueusers] MPI jobs not tied to nodes/ppn configuration

Si Hammond simon.hammond at gmail.com
Thu Oct 15 14:48:27 MDT 2009

Hi Jerry,

> This is dependent on how the scheduler is setup  ( if you allow  
> multiple
> jobs on a single node etc ).
> But I believe you can use:
> qsub -l ncpus=X ...  where X is the total number of cpus you need.

Could you elaborate on what configuration you need for the ncpus  
because I seem to get it queuing as 1 node x 8 tasks which won't ever  
run because we have dual core nodes ( there won't ever be 8 tasks on  
one node ).

The users keep the -l nodes=X:ppn=Y for this reason.

Thanks :)

Simon Hammond
High Performance Systems Group
University of Warwick, UK

> Jerry
> rozelak at volny.cz wrote:
>> Hallo,
>> I have access to heterogeneous clusters with many multi-core/ 
>> processor
>> nodes, where PBSPro is installed. When I want to start MPI job, I  
>> need
>> to specify how many nodes, and how many CPUs per node I want. E.g.,
>> when I require 32 MPI processes, I need to run it as:
>> qsub -l nodes=16:ppn=2 ...
>> The problem is, that PBS will wait until there are at lest 16 nodes,
>> each with 2 cores free, even if there are more that 32 cores free  
>> (e.g.
>> 15 nodes with 2 free cores each + 2 and more nodes with one free  
>> core,
>> giving 32+ free cores available). This can be found for any nodes/ppn
>> combination, e.g.:
>> qsub -l nodes=32:ppn=1 ...
>> will not be started on 31 nodes with 4+ free cores (having 124 cores
>> free!). What I need is just to say -- I need XY cores/processors for
>> my job in a cluster, and I do not care how many nodes it will be  
>> started
>> on, while each node may allocate different number of cores.
>> So, the question is: is 'torque' able to handle such cases? And how?
>> If so, I will talk about it with our clusters admins, as I remember
>> that they considered the migration from PBS and they are opened to  
>> our(users)
>> wishes.
>> Thank you very much for your answer,
>> Dan T.
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Si Hammond

Performance Modelling, Analysis and Optimisation Laboratory
High Performance Systems Group
Department of Computer Science
University of Warwick, CV4 7AL, UK

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