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An Optimal Algorithm for Scheduling Soft Aperiodic Tasks in Dynamic-Priority Preemptive Systems
June 1997 (vol. 23 no. 6)
pp. 388-400

Abstract—This paper addresses the problem of jointly scheduling tasks with both hard and soft real-time constraints. We present a new analysis applicable to systems scheduled using a priority preemptive dispatcher, with priorities assigned dynamically according to the EDF policy. Further, we present a new efficient on-line algorithm (the acceptor algorithm) for servicing aperiodic work load. The acceptor transforms a soft aperiodic task into a hard one by assigning a deadline. Once transformed, aperiodic tasks are handled in exactly the same way as periodic tasks with hard deadlines. The proposed algorithm is shown to be optimal in terms of providing the shortest aperiodic response time among fixed- and dynamic-priority schedulers. It always guarantees the proper execution of periodic hard tasks. The approach is composed of two parts: an off-line analysis and a run-time scheduler. The off-line algorithm runs in pseudopolynomial time O(mn), where n is the number of hard periodic tasks and m is the hyperperiod/min deadline.

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Index Terms:
Dynamic scheduling theory, hard real-time, feasibility analysis, slack scheduling, soft aperiodic tasks, dynamic.
Ismael Ripoll, Alfons Crespo, Ana García-Fornes, "An Optimal Algorithm for Scheduling Soft Aperiodic Tasks in Dynamic-Priority Preemptive Systems," IEEE Transactions on Software Engineering, vol. 23, no. 6, pp. 388-400, June 1997, doi:10.1109/32.601081
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