Towards a Hybrid MPI Correctness Benchmark Suite

Abstract

High-performance computing codes often combine the Message-Passing Interface (MPI) with a shared-memory programming model, e.g., OpenMP, for efficient computations. These so-called hybrid models may issue MPI calls concurrently from different threads at the highest level of MPI thread support. The correct use of either MPI or OpenMP can be complex and error-prone. The hybrid model increases this complexity even further. While correctness analysis tools exist for both programming paradigms, for hybrid models, a new set of potential errors exist, whose detection requires combining knowledge of MPI and OpenMP primitives. Unfortunately, correctness tools do not fully support the hybrid model yet, and their current capabilities are also hard to assess. In previous work, to enable structured comparisons of correctness tools and improve their coverage, we proposed the MPI-CorrBench test suite for MPI. Likewise, others proposed the DataRaceBench test suite for OpenMP. However, for the particular error classes of the hybrid model, no such test suite exists. Hence, we propose a hybrid MPI-OpenMP test suite to (1) facilitate the correctness tool development in this area and, subsequently, (2) further encourage the use of the hybrid model at the highest level of MPI thread support. To that end, we discuss issues with this hybrid model and the knowledge correctness tools need to combine w.r.t. MPI and OpenMP to detect these. In our evaluation of two state-of-the-art correctness tools, we see that for most cases of concurrent and conflicting MPI operations, these tools can cope with the added complexity of OpenMP. However, more intricate errors, where user code interferes with MPI, e.g., a data race on a buffer, still evade tool analysis.