Runtime Correctness Analysis of MPI-3 Nonblocking Collectives

The Message Passing Interface (MPI) includes nonblocking collective operations that support additional overlap between computation and communication. These new operations enable complex data movement between large numbers of processes. However, their asynchronous behavior hides and complicates the detection of defects in their use. We highlight a lack of correctness tool support for these operations and extend the MUST runtime MPI correctness tool to alleviate this complexity. We introduce a classification to summarize the types of correctness analyses that are applicable to MPI's nonblocking collectives. We identify complex wait-for dependencies in deadlock situations and incorrect use of communication buffers as the most challenging types of usage errors. We devise, demonstrate, and evaluate the applicability of correctness analyses for these errors. A scalable analysis mechanism allows our runtime approach to scale with the application. Benchmark measurements highlight the scalability and applicability of our approach at up to 4,096 application processes and with low overhead.