Finite ready queues as a mean for overload reduction in weakly-hard real-time systems
Leonie Ahrendts, Sophie Quinton, Rolf Ernst · 2017
Finite ready queues, implemented by buffers, are a system reality in embedded real-time computing systems and networks. The dimensioning of queues is subject to constraints in industrial practice, and often the queue capacity is sufficient for typical system behavior but is not sufficient in peak overload conditions. This may lead to overflow and consequently to the discarding of jobs. In this paper, we explore whether finite queue capacity can also be used as a mean of design in order to reduce workload peaks and thus shorten a transient overload phase. We present an analysis method which is to the best of our knowledge the first one able to give (a) worst-case response times guarantees as well as (b) weakly-hard guarantees for tasks which are executed on a computing system with finite queues. Experimental results show that finite queue capacity may only a have weak overload limiting effect. This unexpected outcome can be explained by the system behavior in the worst-case corner cases. The analysis shows nevertheless that a trade-off between weakly-hard guarantees and queue sizes is possible.