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Negative results for scheduling independent hard real-time tasks with self-suspensions

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3 Author(s)
F. Ridouard ; LISI-ENSMA, Futuroscope, France ; P. Richard ; F. Cottet

In most real-time systems, tasks use remote operations that are executed upon dedicated processors. External operations introduce self-suspension delays in the behavior of tasks. This paper presents several negative results concerning scheduling independent hard real-time tasks with self-suspensions. Our main objective is to show that well-known scheduling policies such as fixed-priority or earliest deadline first are not efficient to schedule such task systems. We prove the scheduling problem to be NP-hard in the strong sense, even for synchronous task systems with implicit deadlines. We also show that scheduling anomalies can occur at run-time: reducing the execution requirement or the suspension delay of a task can lead the task system to be infeasible under EDF. Lastly, we present negative results on the worst-case performances of well-known scheduling algorithms (EDFy RM, DM, LLF, SRPTF) to maximize tasks completed by their deadlines.

Published in:

Real-Time Systems Symposium, 2004. Proceedings. 25th IEEE International

Date of Conference:

5-8 Dec. 2004