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On the Importance of Parallel Application Placement in NUMA Multiprocessors

Timothy Brecht
Department of Computer Science
University of Toronto
Toronto, Ontario, CANADA


The thesis of this paper is that scheduling decisions in large-scale, shared-memory, NUMA (Non-Uniform Memory Access) multiprocessors must consider not only how many processors, but also which processors to allocate to each application. We call the problem of assigning parallel processes of an application to processors application placement.

We explore the importance of placement decisions by measuring the execution time of several parallel applications using different placements on a shared-memory NUMA multiprocessor. The results of these experiments lead us to conclude that, as expected, in small-scale mildly NUMA multiprocessors, placement decisions have only a minor affect on the execution time of parallel applications. However, the results also show that placement decisions in large-scale multiprocessors are critical and localization that considers the architectural clusters inherent in these systems is essential. Our experiments also show that the importance of placement decisions increases substantially with the size and NUMAness of the system and that the placement of individual processes of an application within the subset of chosen processors also significantly impacts performance.

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