Improved response-time bounds in fixed priority scheduling with arbitrary deadlines

Abstract

We consider fixed priority sporadic tasks with arbitrary deadlines to be executed upon a uni-processor platform. Efficient schedulability tests for this task model are required for both online task admission in dynamic systems and interactive design of complex embedded real-time systems. The paper derives novel continuous upper bounds on the worst-case response times which runs in linear complexity. These bounds are not comparable to the tightest existing continuous upper bound of Bini et al. (in: Proceedings of the IEEE international conference on real-time systems symposium (RTSS’15), San Antonio, 2015) and strictly tighter under some parameters configurations. Moreover, the proposed approach allows to combine various existing methods to produce the tightest known continuous response time bounds. These results are extended to be applicable to a wide range of processor and network scheduling problems, including: release jitters, blocking times and cache related preemption delay (CRPD). Response time upper bounds are also given for tasks that are scheduled pre-emptively, co-operatively with intervals where pre-emption is deferred, and non-preemptively. Lastly, the quality of the method is analyzed and various recommendations are provided by means of numerical experiments.