Abstract
The OpenMP tasking directives promise to help expose a higher degree of concurrency to the runtime than traditional worksharing constructs, which is especially useful for irregular applications. In combination with process-based parallelization such as MPI, the taskyield construct in OpenMP can become a crucial aspect as it helps to hide communication latencies by allowing a thread to execute other tasks while completion of the communication operation is pending. Unfortunately, the OpenMP standard only provides little guarantees on the characteristics of the taskyield operation. In this paper, we explore different potential implementations of taskyield and present a portable black-box tool for detecting the actual implementation used in existing OpenMP compilers/runtimes. Furthermore, we discuss the impact of the different taskyield implementations on the task design of the communication-heavy Blocked Cholesky Factorization and the difference in performance that can be observed, which we found to be over 20 %.
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Notes
- 1.
The full code is available at https://github.com/devreal/omp-taskyield.
- 2.
All code is available at https://github.com/devreal/cholesky_omptasks.
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Acknowledgements
We gratefully acknowledge funding by the German Research Foundation (DFG) through the German Priority Programme 1648 Software for Exascale Computing (SPPEXA) in the SmartDASH project. Part of this work has been supported by the European Community through the project Mont Blanc 3 (H2020 program, grant agreement \(\hbox {N}^{\text {o}}\) 671697). This work was supported by a fellowship within the FITweltweit program of the German Academic Exchange Service (DAAD).
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Schuchart, J., Tsugane, K., Gracia, J., Sato, M. (2018). The Impact of Taskyield on the Design of Tasks Communicating Through MPI. In: de Supinski, B., Valero-Lara, P., Martorell, X., Mateo Bellido, S., Labarta, J. (eds) Evolving OpenMP for Evolving Architectures. IWOMP 2018. Lecture Notes in Computer Science(), vol 11128. Springer, Cham. https://doi.org/10.1007/978-3-319-98521-3_1
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