An OpenMP Parallelisation of Real-time Processing of CERN LHC Beam Position Monitor Data

SUSSIX is a FORTRAN program for the post processing of turn-by-turn Beam Position Monitor (BPM) data, which computes the frequency, amplitude, and phase of tunes and resonant lines to a high degree of precision. For analysis of LHC BPM data a specific version run through a C steering code has been implemented in the CERN Control Centre to run on a server under the Linux operating system but became a real time computational bottleneck preventing truly online study of the BPM data. Timing studies showed that the independent processing of each BPMs data was a candidate for parallelization and the Open Multiprocessing (OpenMP) package with its simple insertion of compiler directives was tried. It proved to be easy to learn and use, problem free and efficient in this case reaching a factor of ten reductions in real-time over twelve cores on a dedicated server. This paper reviews the problem, shows the critical code fragments with their OpenMP directives and the results obtained.