Process Mapping for MPI Collective Communications

It is an important problem to map virtual parallel processes to physical processors (or cores) in an optimized way to get scalable performance due to non-uniform communication cost in modern parallel computers. Existing work uses profile-guided approaches to optimize mapping schemes to minimize the cost of point-to-point communications automatically. However, these approaches cannot deal with collective communications and may get sub-optimal mappings for applications with collective communications. In this paper, we propose an approach called OPP (Optimized Process Placement) to handle collective communications which transforms collective communications into a series of point-to-point communication operations according to the implementation of collective communications in communication libraries. Then we can use existing approaches to find optimized mapping schemes which are optimized for both point-to-point and collective communications. We evaluated the performance of our approach with micro-benchmarks which include all MPI collective communications, NAS Parallel Benchmark suite and three other applications. Experimental results show that the optimized process placement generated by our approach can achieve significant speedup.