Dynamic Scheduling of Skippable Periodic Tasks: Issues and Proposals

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.