Non-clairvoyant batch sets scheduling: fairness is fair enough

  • Authors:
  • Julien Robert;Nicolas Schabanel

  • Affiliations:
  • École Normale Supérieure de Lyon, Lyon Cedex 07, France;CNRS, Centro de Modelamiento Matemático, Santiago de Chile

  • Venue:
  • ESA'07 Proceedings of the 15th annual European conference on Algorithms
  • Year:
  • 2007

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Abstract

In real systems, such as operating systems, the scheduler is often unaware of the remaining work in each job or of the ability of the job to take advantage of more resources. In this paper, we adopt the setting for non-clairvoyance of [3,2]. Based on the particular case of malleable jobs, it is generally assumed in the literature that "Equi never starves a job since it allocates to every job the same amount of processing power". We provide an analysis of the competitiveness of Equi for the makespan objective which shows that under this more general setting this statement is at the same time true and false: false, because, some jobs may be stretched by a factor as large as, but no more than, lnn/ln ln n with respect to the optimal, where n is the size of the largest set; true, because no algorithm can achieve a better competitive ratio up to a constant factor. In this paper, we extend the results in [2,11] to the batch scheduling of sets of jobs that go through arbitrary phases: user request all together at time 0, for the execution of a set of jobs and is served when the last job completes. We prove that the algorithm EquioEqui is (2 + √3 + o(1)) lnn/ln ln n-competitive, where n is the maximum size of a set, which is optimal up to a constant factor. We provide experimental evidences that this algorithm may have the same asymptotic competitive ratio Θ(lnn/ln ln n) (independent of the number of requests) for the flowtime objective when requests have release dates, if it is given sufficiently large extra processing power with respect to the optimum.