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openmp-lab-exercises

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    advanced_lab
    intro_lab
    LICENSE.md
    OpenMP3.0-FortranCard.pdf
    OpenMP3.0-SummarySpec.pdf
    README.md
    README.md

    Instructions and hints on how to run for the OpenMP lab

    Where to run

    The exercises will be run on PDC's CRAY XC-40 system Beskow:

    beskow.pdc.kth.se

    How to login

    To access PDC's cluster you should use your laptop and the Eduroam or KTH Open wireless networks.

    Instructions on how to connect from various operating systems.

    More about the environment on Beskow

    The Cray automatically loads several modules at login.

    Compiling MPI programs on Beskow

    By default the cray compiler is loaded into your environment. In order to use another compiler you have to swap compiler modules:

    module swap PrgEnv-cray PrgEnv-gnu

    or

    module swap PrgEnv-cray PrgEnv-intel

    On Beskow one should always use the compiler wrappers cc, CC or ftn (for C, C++ and Fortran codes, respectively), which will automatically link to MPI libraries and linear algebra libraries like BLAS, LAPACK, etc.

    Examples:

    # Intel
ftn -openmp source.f90
cc -openmp source.c
CC -openmp source.cpp
# Cray
ftn -openmp source.f90
cc -openmp source.c
CC -openmp source.cpp
# GNU
ftn -fopenmp source.f90
cc -fopenmp source.c
CC -fopenmp source.cpp

    Running OpenMP programs on Beskow

    After having compiled your code with the correct compilers flags for OpenMP, it is necessary to book a node for interactive use:

    salloc -A <allocation-name> -N 1 -t 1:0:0

    You might also need to specify a reservation by adding the flag --reservation=<name-of-reservation>.

    An environment variable specifying the number of threads should also be set:

    export OMP_NUM_THREADS=32

    Then the srun command is used to launch an OpenMP application:

    srun -n 1 ./example.x

    In this example we will start one task with 32 threads (there are 32 cores per node on the Beskow nodes).

    It is important to use the srun command since otherwise the job will run on the Beskow login node.

    OpenMP Exercises

    The aim of these exercises is to give an introduction to OpenMP programming. All examples are available in both C and Fortran90.