JOURNAL OF SOFTWARE (JSW)
ISSN : 1796-217X
Volume : 2    Issue : 5    Date : November 2007

Dynamic Scheduling of Skippable Periodic Tasks: Issues and Proposals
Maryline Silly-Chetto and Audrey Marchand
Page(s): 44-51
Full Text:
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Abstract
This paper deals with dynamic scheduling in realtime systems that have Quality of Service
requirements. We assume that tasks are periodic and may miss their deadlines, occasionally, as
defined by the so-called Skip-Over model. In this paper, we present a dynamic scheduling
algorithm, called RLP (Red as Late as possible, a variant of Earliest Deadline to make slack
stealing and to get better performance in terms of ratio of periodic task instances which complete
before their deadline). Simulation results show that RLP outperforms the two conventional skip-over
algorithms, namely RTO and BWP, introduced about ten years ago. Then, we investigate a second
criteria called fairness, aiming to balance individual success ratios of tasks. We present variants of
RLP to improve fairness and report comparative simulation results. Finally, we present the
integration of these QoS scheduling services into CLEOPATRE1, a free open-source library which
offers selectable real-time facilities on shelves.

Index Terms
Real-time scheduling, Earliest Deadline, Fairness, Component-based architectures, Operating
systems, Real-time Linux.