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Subject: Re: [OMPI users] running external program on same processor (Fortran)
From: Terry Frankcombe (terry_at_[hidden])
Date: 2010-03-03 20:50:39


On Wed, 2010-03-03 at 12:57 -0500, Prentice Bisbal wrote:
> Reuti wrote:
> > Are you speaking of the same?
>
> Good point, Reuti. I was thinking of a cluster scheduler like SGE or
> Torque.

Yeah, I meant the scheduler in the CPU time slice sense.

http://en.wikipedia.org/wiki/Scheduling_(computing)
vs.
http://en.wikipedia.org/wiki/Job_scheduler

> > Am 03.03.2010 um 17:32 schrieb Prentice Bisbal:
> >
> >> Terry Frankcombe wrote:
> >>> Surely this is the problem of the scheduler that your system uses,
> >
> > This I would also state.
> >
> >
> >>> rather than MPI?
> >
> > Scheduler in the Linux kernel?
> >
> >
> >> That's not true. The scheduler only assigns the initial processes to
> >> nodes
> >
> > Scheduler in MPI?
> >
> >
> >> and starts them. It can kill the processes it starts if they use
> >> too much memory or run too long, but doesn't prevent them from spawning
> >> more processes, and once spawned,
> >
> > When the processes are bound to one and the same core, these addititonal
> > processes won't intefere with other jobs' processes on the same node
> > which run on the other cores.
> >
> > -- Reuti
> >
> >
> >> unless they are spawned through the
> >> scheduler, it has no control over them.
> >>>
> >>>
> >>> On Wed, 2010-03-03 at 00:48 +0000, abc def wrote:
> >>>> Hello,
> >>>>
> >>>> I wonder if someone can help.
> >>>>
> >>>> The situation is that I have an MPI-parallel fortran program. I run it
> >>>> and it's distributed on N cores, and each of these processes must call
> >>>> an external program.
> >>>>
> >>>> This external program is also an MPI program, however I want to run it
> >>>> in serial, on the core that is calling it, as if it were part of the
> >>>> fortran program. The fortran program waits until the external program
> >>>> has completed, and then continues.
> >>>>
> >>>> The problem is that this external program seems to run on any core,
> >>>> and not necessarily the (now idle) core that called it. This slows
> >>>> things down a lot as you get one core doing multiple tasks.
> >>>>
> >>>> Can anyone tell me how I can call the program and ensure it runs only
> >>>> on the core that's calling it? Note that there are several cores per
> >>>> node. I can ID the node by running the hostname command (I don't know
> >>>> a way to do this for individual cores).
> >>>>
> >>>> Thanks!
> >>>>
> >>>> ====
> >>>>
> >>>> Extra information that might be helpful:
> >>>>
> >>>> If I simply run the external program from the command line (ie, type
> >>>> "/path/myprogram.ex <enter>"), it runs fine. If I run it within the
> >>>> fortran program by calling it via
> >>>>
> >>>> CALL SYSTEM("/path/myprogram.ex")
> >>>>
> >>>> it doesn't run at all (doesn't even start) and everything crashes. I
> >>>> don't know why this is.
> >>>>
> >>>> If I call it using mpiexec:
> >>>>
> >>>> CALL SYSTEM("mpiexec -n 1 /path/myprogram.ex")
> >>>>
> >>>> then it does work, but I get the problem that it can go on any core.
> >>>>
> >>>> ______________________________________________________________________
> >>>> Do you want a Hotmail account? Sign-up now - Free
> >>>> _______________________________________________
> >>>> users mailing list
> >>>> users_at_[hidden]
> >>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
> >>>
> >>> _______________________________________________
> >>> users mailing list
> >>> users_at_[hidden]
> >>> http://www.open-mpi.org/mailman/listinfo.cgi/users
> >>>
> >>
> >> --
> >> Prentice Bisbal
> >> Linux Software Support Specialist/System Administrator
> >> School of Natural Sciences
> >> Institute for Advanced Study
> >> Princeton, NJ
> >> _______________________________________________
> >> users mailing list
> >> users_at_[hidden]
> >> http://www.open-mpi.org/mailman/listinfo.cgi/users
> >
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
> >
>