Even though the Open Science Pool is a high throughput computing system, sometimes there is a need to run small OpenMPI based jobs. OSG has limited support for this, as long as the core count is small (4 is known to work well, 8 and 16 becomes more difficult due to the limited number of resources).

    To get started, first compile your code using the OpenMPI in the modules system. For example:

    $ module load openmpi
    $ mpicc -o hello hello.c

    You can test the executable locally using mpiexec:

    $ mpiexec -n 4 hello
    Hello world from process 1 of 4
    Hello world from process 3 of 4
    Hello world from process 0 of 4
    Hello world from process 2 of 4

    To run your code as a job on the Open Science Pool, first create a wrapper.sh. Example:

    set -e
    module load openmpi
    mpiexec -n 4 hello

    Then, a job submit file:

    Requirements = OSGVO_OS_STRING == "RHEL 7" && TARGET.Arch == "X86_64" && HAS_MODULES == True 
    request_cpus = 4
    request_memory = 4 GB
    executable = wrapper.sh
    transfer_input_files = hello
    output = job.out.$(Cluster).$(Process)
    error = job.error.$(Cluster).$(Process)
    log = job.log.$(Cluster).$(Process)
    queue 1

    Note how the executable is the wrapper.sh script, and that the real executable hello is transferred using the transfer_input_files mechanism.

    Please make sure that the number of cores specified in the submit file via request_cpus match the -n argument in the wrapper.sh file.


    This page was updated on Jan 25, 2022 at 14:36 from start/resources/openmpi-jobs.md.