RAHTM: Routing Algorithm Aware Hierarchical Task Mapping

The mapping of MPI processes to compute nodes on a supercomputer can have a significant impact on communication performance. For high performance computing (HPC) applications with iterative communication, rich offline analysis of such communication can improve performance by optimizing the mapping. Unfortunately, current practices for at-scale HPC consider only the communication graph and network topology in solving this problem. We propose Routing Algorithm aware Hierarchical Task Mapping (RAHTM) which leverages the knowledge of the routing algorithm to improve task mapping. RAHTM achieves high quality mappings by combining (1) a divide-and-conquer strategy to achieve scalability, (2) a limited search of mappings, and (3) a linear programming based routing-aware approach to evaluate possible mappings in the search space. RAHTM achieves 20% reduction in the communication time and 9% reduction in the overall execution time for three communication-heavy benchmarks scaled up to 16,384 processes on a Blue Gene/Q platform.