Lightweight Task Offloading Exploiting MPI Wait Times for Parallel Adaptive Mesh Refinement

Samfass, Philipp; Weinzierl, Tobias; Charrier, Dominic E.; Bader, Michael

doi:10.1002/cpe.5916

Lightweight Task Offloading Exploiting MPI Wait Times for Parallel Adaptive Mesh Refinement

Samfass, Philipp; Weinzierl, Tobias; Charrier, Dominic E.; Bader, Michael

Authors

Philipp Samfass

Professor Tobias Weinzierl tobias.weinzierl@durham.ac.uk
Professor

Dominic E. Charrier

Michael Bader

Abstract

Balancing the workload of sophisticated simulations is inherently difficult, since we have to balance both computational workload and memory footprint over meshes that can change any time or yield unpredictable cost per mesh entity, while modern supercomputers and their interconnects start to exhibit fluctuating performance. We propose a novel lightweight balancing technique for MPI+X to accompany traditional, prediction‐based load balancing. It is a reactive diffusion approach that uses online measurements of MPI idle time to migrate tasks temporarily from overloaded to underemployed ranks. Tasks are deployed to ranks which otherwise would wait, processed with high priority, and made available to the overloaded ranks again. This migration is nonpersistent. Our approach hijacks idle time to do meaningful work and is totally nonblocking, asynchronous and distributed without a global data view. Tests with a seismic simulation code developed in the ExaHyPE engine uncover the method's potential. We found speed‐ups of up to 2‐3 for ill‐balanced scenarios without logical modifications of the code base and show that the strategy is capable to react quickly to temporarily changing workload or node performance.

Citation

Samfass, P., Weinzierl, T., Charrier, D. E., & Bader, M. (2020). Lightweight Task Offloading Exploiting MPI Wait Times for Parallel Adaptive Mesh Refinement. Concurrency and Computation: Practice and Experience, 32(24), Article e5916. https://doi.org/10.1002/cpe.5916

Journal Article Type	Article
Acceptance Date	May 18, 2020
Online Publication Date	Jul 9, 2020
Publication Date	Dec 25, 2020
Deposit Date	May 18, 2020
Publicly Available Date	Jul 17, 2020
Journal	Concurrency and Computation: Practice and Experience
Print ISSN	1532-0626
Publisher	Wiley
Peer Reviewed	Peer Reviewed
Volume	32
Issue	24
Article Number	e5916
DOI	https://doi.org/10.1002/cpe.5916
Related Public URLs	https://arxiv.org/abs/1909.06096

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http://creativecommons.org/licenses/by/4.0/

Copyright Statement
Advance online version © 2020 The Authors. Concurrency and Computation: Practice and Experience published by John Wiley & Sons, Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.