Traffic Shaping in Real-Time Distributed Systems: a Low-Complexity Approach
Résumé
In real-time systems, one generally identifies two types of timing requirement- s, hard and soft constraints. In this study, it is assumed that the Hard Real-Time traffic (HRT) is periodic with deadlines that must be guaranteed, while the Soft Real-Time traffic (SRT) is aperiodic with timing constraints that could occasionally be missed without major consequences. In this paper, the problem of scheduling these 2 types of traffic with different performance objectives will be addressed : (1) ensure that the timing requirements of HRT traffic are met, (2) minimize as much as possible the response time of SRT traffic while satisfying (1). For this purpose, we propose an easily implementable and low-complexity traffic shaping policy which preserves feasibility and improves response times for SRT traffic. The underlying idea is that it is possible to diminish the response time of SRT traffic if the busy periods induced by the HRT traffic are "harmoniously" distributed over time, creating time intervals during which the resource (i.e. the processor or the medium) can be used by SRT traffic with minimum delay. A computer-implementable algorithm that has to be executed independently on each node of the bus is also provided, as well as several extensions of the original model.