Runtime Support for Multigrain and Multiparadigm Parallelism

This paper presents a general methodology for implementing on clusters the runtime support for a two-level dependence-driven thread model, initially targeted to shared-memory multiprocessors. The general ideal is to exploit existing programming solutions for these architectures, like Software DSM (SWDSM) and Message Passing Interface. The management of the internal runtime system structures and of the dependence-driven multilevel parallelism is performed with explicit messages, exploiting however the shared-memory hardware of the available SMP nodes whenever this is possible. The underlying programming models and hybrid programming solutions are not excluded, using threads for the intra-node parallelism. The utilization of shared virtual memory for thread stacks and a translator for allocating Fortran77 common blocks in shared memory enable the execution of unmodified OpenMP codes on clusters of SMPs. Initial performance results demonstrate the efficient support for fork-join and multilevel parallelism on top of SWDSM and MPI and confirm the benefits of explicit, though transparent, message passing.