Dover: An Optimal On-Line Scheduling Algorithm for Overloaded Uniprocessor Real-Time Systems

  • Authors:
  • Gilad Koren;Dennis Shasha

  • Affiliations:
  • -;-

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 1995

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Abstract

Consider a real-time system in which every task has a value that it obtains only if it completes by its deadline. The problem is to design an on-line scheduling algorithm (i.e., the scheduler has no knowledge of a task until it is released) that maximizes the guaranteed value obtained by the system. When such a system is underloaded (i.e., there exists a schedule for which all tasks meet their deadlines), Dertouzos [Proceedings IFIF Congress, 1974, pp.\ 807--813] showed that the earliest deadline first algorithm will achieve 100% of the possible value. Locke [Ph. D. thesis, Computer Science Dept., Carnegie-Mellon Univ., Pittsburgh, PA] showed that earliest deadline first performs very badly, however, when the system is overloaded, and he proposed heuristics to deal with overload. This paper presents an optimal on-line scheduling algorithm for overloaded uniprocessor systems. It is optimal in the sense that it gives the best competitive ratio possible relative to an off-line scheduler.