PARCOACH: Combining static and dynamic validation of MPI collective communications

摘要

Nowadays most scientific applications are parallelized based on MPI communications. Collective MPI communications have to be executed in the same order by all processes in their communicator and the same number of times, otherwise they do not conform to the standard and a deadlock or other undefined behaviour can occur. As soon as the control flow involving these collective operations becomes more complex, in particular including conditionals on process ranks, ensuring the correction of such code is error-prone. We propose in this paper a static analysis to detect when such a situation occurs, combined with a code transformation that prevents deadlocking. We focus on blocking MPI collective operations in single program multiple data applications, assuming MPI calls are not nested in multithreaded regions. We show on several benchmarks the small impact on performance and the ease of integration of our techniques in the development process.