[GE users] controlling openmp jobs

Reuti reuti at staff.uni-marburg.de
Thu May 5 10:10:10 BST 2005


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Hi Shing,

you can't control the creation of forks/threads. You often also see additional 
forks in MPICH jobs which will handle the communication, but not using up any 
CPU time (besides the communication). It's of course correct, that an OpenMP 
job should also be submitted to a PE for proper slot allocation, although you 
don't have to setup anyting there for the job.

Maybe seeing the slots from a different view will explain it to the users: 
getting one slot of a dual CPU machine means "give me half of the CPU power of 
this machine". Whether the user starts a pur serial job or creats an additonal 
fork/thread: he/she will get half of the total CPU time (unless there is 
nothing else running).

HTH - Reuti

Quoting shing at cz3.nus.edu.sg:

> 
> hi,
> 
> I wondering how other people are controlling their openmp jobs. Ideally of
> course, openmp jobs should be submitted in a PE. However there's nothing
> to stop openmp jobs from being submitted to a serial queue since SGE won't
> be able to tell that it is an openmp job, and if the job gets scheduled on
> a 2-cpu machine with 2 slots, it will use both cpus, effectively using up
> 2 slots but SGE only records it as 1 slot. How can we get SGE to force
> openmp jobs to use an appropriate PE? Perhaps the OMP_NUM_THREADS env var
> can be set during submission? ie. if submitted to a serial queue,
> OMP_NUM_THREADS gets set to 1 (without the user being able to override)
> and the job uses 1 slot. Could that be done?  If so, how?
> 
> thanks,
> --shing
> 
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