Improving load balance with flexibly assignable tasks

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In many applications of parallel computing, distribution ofthe data unambiguously implies distribution of work among processors. Butthere are exceptions where some tasks can be assigned to one of severalprocessors without altering the total volume of communication. In thispaper, we study the problem of exploiting this flexibility in assignmentof tasks to improve load balance. We first model the problem in terms ofnetwork flow and use combinatorial techniques for its solution. Ourparametric search algorithms use maximum flow algorithms for probing on acandidate optimal solution value. We describe two algorithms to solve theassignment problem with \logW_T and vbar P vbar probe calls, w ... continued below

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Pinar, Ali & Hendrickson, Bruce September 9, 2003.

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In many applications of parallel computing, distribution ofthe data unambiguously implies distribution of work among processors. Butthere are exceptions where some tasks can be assigned to one of severalprocessors without altering the total volume of communication. In thispaper, we study the problem of exploiting this flexibility in assignmentof tasks to improve load balance. We first model the problem in terms ofnetwork flow and use combinatorial techniques for its solution. Ourparametric search algorithms use maximum flow algorithms for probing on acandidate optimal solution value. We describe two algorithms to solve theassignment problem with \logW_T and vbar P vbar probe calls, w here W_Tand vbar P vbar, respectively, denote the total workload and number ofproce ssors. We also define augmenting paths and cuts for this problem,and show that anyalgorithm based on augmenting paths can be used to findan optimal solution for the task assignment problem. We then consideracontinuous version of the problem, and formulate it as a linearlyconstrained optimization problem, i.e., \min\|Ax\|_\infty,\; {\rms.t.}\;Bx=d. To avoid solving an intractable \infty-norm optimization problem,we show that in this case minimizing the 2-norm is sufficient to minimizethe \infty-norm, which reduces the problem to the well-studiedlinearly-constrained least squares problem. The continuous version of theproblem has the advantage of being easily amenable to parallelization.Our experiments with molecular dynamics and overlapped domaindecomposition applications proved the effectiveness of our methods withsignificant improvements in load balance. We also discuss how ourtechniques can be enhanced for heterogeneous systems.

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  • Journal Name: IEEE Transactions on Parallel and DistributedSystems; Journal Volume: 16; Journal Issue: 10; Related Information: Journal Publication Date: 10/2005

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  • Report No.: LBNL--53758
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 860216
  • Archival Resource Key: ark:/67531/metadc782374

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  • September 9, 2003

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  • Dec. 3, 2015, 9:30 a.m.

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  • April 1, 2016, 7:38 p.m.

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Pinar, Ali & Hendrickson, Bruce. Improving load balance with flexibly assignable tasks, article, September 9, 2003; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc782374/: accessed August 16, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.