Surely this is the problem of the scheduler that your system uses,
rather than MPI?
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.
>
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