[GE users] controlling openmp jobs

shing at cz3.nus.edu.sg shing at cz3.nus.edu.sg
Fri May 6 08:28:02 BST 2005


hi ron,

I have linux26 (on x86 and amd64), tru64, hpux (on ia64). How do I use
cpusets? Could you point me to some docs on it?

What do you think of the OMP_NUM_THREADS idea? That should work on all
platforms.

thanks,
--shing

On Thu, 5 May 2005, Ron Chen wrote:

> Shing, what OS is it? Some operating systems allow
> binding processes to CPUSets. So an OpenMP job binded
> to a processer can only use that CPU, which is eactly
> what you want!
>
> SGE supports CPUsets on Solaris, IRIX, and tru64, and
> IA64 Linux. With some minor work, we can get CPUSet
> support on all Linux 2.6 platforms.
>
>  -Ron
>
> --- Reuti <reuti at staff.uni-marburg.de> wrote:
> > 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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