Abstract
Optimizing scientific applications on today's accelerator-based high performance computing systems can be challenging, especially when multiple GPUs and CPUs with heterogeneous memories and persistent non-volatile memories are present. An example is Summit, an accelerator-based system at the Oak Ridge Leadership Computing Facility (OLCF) that is rated as the world's fastest supercomputer to-date. New strategies are thus needed to expose the parallelism in legacy applications, while being amenable to efficient mapping to the underlying architecture. In this paper we discuss our experiences and strategies to port a scientific application, DCA++, to Summit. DCA++ is a high-performance research application that solves quantum many-body problems with a cutting edge quantum cluster algorithm, the dynamical cluster approximation. Our strategies aim to synergize the strengths of the different programming models in the code. These include: A) streamlining the interactions between the CPU threads and the GPUs, b) implementing computing kernels on the GPUs and decreasing CPU-GPU memory transfers, c) allowing asynchronous GPU communications, and d) increasing compute intensity by combining linear algebraic operations. Full-scale production runs using all 4600 Summit nodes attained a peak performance of 73.5 PFLOPS with a mixed precision implementation. We observed a perfect strong and weak scaling for the quantum Monte Carlo solver in DCA++, while encountering about 2x input/output (I/O) and MPI communication overhead on the time-To-solution for the full machine run. Our hardware agnostic optimizations are designed to alleviate the communication and I/O challenges observed, while improving the compute intensity and obtaining optimal performance on a complex, hybrid architecture like Summit.
Original language | English |
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Title of host publication | Proceedings - 2019 28th International Conference on Parallel Architectures and Compilation Techniques, PACT 2019 |
Publisher | Institute of Electrical and Electronics Engineers Inc. |
Pages | 432-443 |
Number of pages | 12 |
ISBN (Electronic) | 9781728136134 |
DOIs | |
State | Published - Sep 2019 |
Event | 28th International Conference on Parallel Architectures and Compilation Techniques, PACT 2019 - Seattle, United States Duration: Sep 21 2019 → Sep 25 2019 |
Publication series
Name | Parallel Architectures and Compilation Techniques - Conference Proceedings, PACT |
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Volume | 2019-September |
ISSN (Print) | 1089-795X |
Conference
Conference | 28th International Conference on Parallel Architectures and Compilation Techniques, PACT 2019 |
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Country/Territory | United States |
City | Seattle |
Period | 09/21/19 → 09/25/19 |
Funding
This manuscript has been co-authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). ¶All three authors have equal contribution to the manuscript. † Ying Wai Li contributed to this work mostly during her previous appointment at Oak Ridge National Laboratory, Oak Ridge 37831, U.S. Authors would like to thank Oscar Hernandez (ORNL), Jeff Larkin (NVIDIA), Don Maxwell (ORNL), Ronny Bren-del (Score-P), John Mellor-Crummey (HPCToolkit) for their insights during the optimization phase of DCA++. This work was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences, Division of Materials Sciences and Engineering. This research used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725.
Keywords
- CUDA
- CUDA aware MPI
- DCA
- QMC
- Quantum Monte Carlo
- Spectrum MPI
- Summit@OLCF