Adding OpenMP to an existing MPI code: will it be beneficial?

Summary form only given, as follows. ICEPIC (Improved Concurrent Electromagnetic Particle In Cell), developed at the Air Force Research Laboratory, is a 3-D and 2-D parallel Particle-In-Cell (PIC) code that was specifically designed to execute efficiently on parallel high performance computing (HPC) resources using the MPI message passing standard. Its primary application is to simulate collisionless plasma physics in high-power microwave devices. ICEPIC has several novel features that allow efficient use of parallel architectures. It is written in ANSI C and uses the MPI message passing standard to provide portability to a variety of HPC systems. Recently, we have been computing on an IBM SMP with 8-way Power3 nodes using only MPI. OpenMP can increase the efficiency and/or scalability of a code executing on shared-memory architectures, such as the IBM SMP. The addition of OpenMP to ICEPIC required minor code modifications. The efficacy of the OpenMP is demonstrated with test problems.