Abstract
The MPI multithreading model has been historically difficult to optimize; the interface that it provides for threads was designed as a process-level interface. This model has led to implementations that treat function calls as critical regions and protect them with locks to avoid race conditions. We hypothesize that an interface designed specifically for threads can provide superior performance than current approaches and even outperform single-threaded MPI.
In this paper, we describe a design for partitioned communication in MPI that we call finepoints. First, we assess the existing communication models for MPI two-sided communication and then introduce finepoints as a hybrid of MPI models that has the best features of each existing MPI communication model. In addition, “partitioned communication” created with finepoints leverages new network hardware features that cannot be exploited with current MPI point-to-point semantics, making this new approach both innovative and useful both now and in the future.
To demonstrate the validity of our hypothesis, we implement a finepoints library and show improvements against a state-of-the-art multithreaded optimized Open MPI implementation on a Cray XC40 with an Aries network. Our experiments demonstrate up to a 12\(\times \) reduction in wait time for completion of send operations. This new model is shown working on a nuclear reactor physics neutron-transport proxy-application, providing up to 26.1% improvement in communication time and up to 4.8% improvement in runtime over the best performing MPI communication mode, single-threaded MPI.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This research was supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of the U.S. Department of Energy Office of Science and the National Nuclear Security Administration.
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Grant, R.E., Dosanjh, M.G.F., Levenhagen, M.J., Brightwell, R., Skjellum, A. (2019). Finepoints: Partitioned Multithreaded MPI Communication. In: Weiland, M., Juckeland, G., Trinitis, C., Sadayappan, P. (eds) High Performance Computing. ISC High Performance 2019. Lecture Notes in Computer Science(), vol 11501. Springer, Cham. https://doi.org/10.1007/978-3-030-20656-7_17
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