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.

• Heimdal - Kerberos commands
• OpenAFS - AFS commands
• SLURM - batch jobs and interactive jobs
• Software development - Programming environments and compilers

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.

• OpenMP Intro lab:
  • Instructions
  • Simple hello world program in C and in Fortran
  • Calculate π in C and in Fortran
  • Solutions will be made available later during the lab
• OpenMP Advanced Lab:
  • Instructions
  • In C: shwater2d.c, vtk_export.c and Makefile
  • In Fortran: shwater2d.f90, vtk_export.f90 and Makefile
  • Solutions will be made available later during the lab