Response time analysis for tasks scheduled under EDF within fixed priorities

Hierarchical schedulers are getting increased attention in many research projects because they bring in flexibility, they can take advantage of the best features of different scheduling policies, and allow the composability of applications developed under different scheduling strategies. Most commercial real-time operating systems have an underlying fixed priority schedule, and for this reason it is necessary to be able to analyze hierarchically-scheduled applications in which the underlying scheduler is of that kind. In this paper we extend the classic response time analysis techniques to analyze applications which can have a mixture of tasks scheduled either with fixed priorities, or with an earliest deadline first (EDF) scheduler running on top of an underlying fixed priority scheduler. We show that the complexity of this analysis is similar to that of existing response time analysis for EDF tasks.