Exploitation of Dynamic Communication Patterns through Static Analysis

Collective operations can have a large impact on the performance of parallel applications. However, the ideal implementation of a particular collective communication often depends on both the application and the targeted machine structure. Our approach combines dynamic and static analysis techniques to identify common collective communication patterns expressed as point-to-point calls and transforms them into equivalent MPI collectives. We first detect potential collective communication patterns in runtime traces and associate them with the corresponding source code regions. If our static analysis verifies that the introduction of collectives is safe for any program flow, we then replace the original communication primitives with their collective counterpart. In this paper we introduce the necessary algorithms to determine the safety of these transformations and we demonstrate several use cases, including automatic use of new extensions to the MPI standard such as nonblocking collective operations. The use of dynamic analysis significantly reduces compile times, resulting in a speed-up of about 50 for source transformations of HPL due to more directed analysis capabilities and also dramatically decreases complexity of the underlying static analysis.