A Runtime System Architecture for Ubiquitous Support of OpenMP

In this work we present the runtime architecture of the OMPi OpenMP compiler. OMPi is a source-to-source C translator featuring a portable, modular and extensible runtime system. It allows for OpenMP threads to map to different execution entities which range from kernel/user-level threads to processes, providing transparent support of OpenMP applications on both SMP machines and clusters of SMPs. When operating within an SMP machine, arbitrary threading libraries can be employed; currently a multitude of such libraries is available, including one which is based on portable user-level threading, for high-performance nested parallelism support. When operating on a cluster, processes are used as the execution entities and different software DSM cores can be utilized under a unified interface; the runtime system uses a hybrid approach whereby its internal bookkeeping is done through explicit message passing, while user-program shared variables are handled by the DSM core.