OpenMP

Overview

OpenMP is one of the emerging standards in shared memory programming. It has a simple API composed of a small set of runtime library routines, compiler directives and environment variables to achieve multi-threaded shared memory parallelism in C/C++ and Fortran codes. OpenMP is a standard that is maintained by the OpenMP Architecture Review Board which consists of a number hardware and software vendors. It's simple interface quickly allows codes to be parallelised gaining decent scalability on small numbers of processors.

Restrictions on Use

Not all the OpenMP 2 features are in the compilers available on our system, for instance the workshare directive is not available on Newton.

Set Up Procedure

Library calls and/or compiler directives are been inserted into the code and are then activated by inclusion of the -mp flag on the Origins and the -openmp on the Altix.

Running the Code

Codes should then be run as serial codes with the environment variable OMP_NUM_THREADS controlling the number of processors to be used.

Further Information

Further information is available at:

• The OpenMP website.
• Our OpenMP Course.
• There is some good reference information at Lawrence Livermore National Laboratory website.