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Early Experiences Co-Scheduling Work and Communication Tasks for Hybrid MPI+X Applications

Proceedings of ExaMPI 2014: Exascale MPI 2014 - held in conjunction with SC 2014: The International Conference for High Performance Computing, Networking, Storage and Analysis

Stark, Dylan S.; Barrett, Richard F.; Grant, Ryan E.; Olivier, Stephen L.; Laros, James H.; Vaughan, Courtenay T.

Advances in node-level architecture and interconnect technology needed to reach extreme scale necessitate a reevaluation of long-standing models of computation, in particular bulk synchronous processing. The end of Dennard-scaling and subsequent increases in CPU core counts each successive generation of general purpose processor has made the ability to leverage parallelism for communication an increasingly critical aspect for future extreme-scale application performance. But the use of massive multithreading in combination with MPI is an open research area, with many proposed approaches requiring code changes that can be unfeasible for important large legacy applications already written in MPI. This paper covers the design and initial evaluation of an extension of a massive multithreading runtime system supporting dynamic parallelism to interface with MPI to handle fine-grain parallel communication and communication-computation overlap. Our initial evaluation of the approach uses the ubiquitous stencil computation, in three dimensions, with the halo exchange as the driving example that has a demonstrated tie to real code bases. The preliminary results suggest that even for a very well-studied and balanced workload and message exchange pattern, co-scheduling work and communication tasks is effective at significant levels of decomposition using up to 131,072 cores. Furthermore, we demonstrate useful communication-computation overlap when handling blocking send and receive calls, and show evidence suggesting that we can decrease the burstiness of network traffic, with a corresponding decrease in the rate of stalls (congestion) seen on the host link and network.

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TYPE Conference Poster YEAR 2014
DOIOSTIScopus

Reducing the bulk of the bulk synchronous parallel model

Parallel Processing Letters

Barrett, Richard F.; Vaughan, Courtenay T.; Hammond, Simon D.

For over two decades the dominant means for enabling portable performance of computational science and engineering applications on parallel processing architectures has been the bulk-synchronous parallel programming (BSP) model. Code developers, motivated by performance considerations to minimize the number of messages transmitted, have typically pursued a strategy of aggregating message data into fewer, larger messages. Emerging and future high-performance architectures, especially those seen as targeting Exascale capabilities, provide motivation and capabilities for revisiting this approach. In this paper we explore alternative configurations within the context of a large-scale complex multi-physics application and a proxy that represents its behavior, presenting results that demonstrate some important advantages as the number of processors increases in scale.

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TYPE Journal Article YEAR 2013
OSTIDOI

Assessing the predictive capabilities of mini-applications

Proceedings - 2012 SC Companion: High Performance Computing, Networking Storage and Analysis, SCC 2012

Barrett, Richard F.; Crozier, Paul C.; Doerfler, Douglas W.; Hammond, Simon D.; Heroux, Michael A.; Lin, Paul L.; Trucano, Timothy G.; Vaughan, Courtenay T.; Williams, Alan B.

The push to exascale computing is informed by the assumption that the architecture, regardless of the specific design, will be fundamentally different from petascale computers. The Mantevo project has been established to produce a set of proxies, or 'miniapps,' which enable rapid exploration of key performance issues that impact a broad set of scientific applications programs of interest to ASC and the broader HPC community. Understanding the conditions under which a miniapp can be confidently used as predictive of an applications' behavior must be clearly elucidated. Toward this end, we have developed a methodology for assessing the predictive capabilities of application proxies. Adhering to the spirit of experimental validation, our approach provides a framework for examining data from the application with that provided by their proxies. In this poster we present this methodology, and apply it to three miniapps developed by the Mantevo project. © 2012 IEEE.

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TYPE Conference YEAR 2012
OSTIScopus
Results 51–75 of 132
Results 51–75 of 132