Characterizing variable task releases and processor capacities

For the schedulability analysis of hard real-time systems it is important to use task and resource models that appropriately capture the particular characteristics of the underlying system. In this paper we suggest new task and processor models, the Variable Task Model and Variable Processor Model, respectivly. The new task model is most appropriate for tasks with bursty release characteristics, and the processor model allows to take into account dead time and variable processing speed. These models are inspired by results from the networking domain [5], but our presentation emphasizes the dual nature of arrival and service curves. Some new properties of service curves are proven. As an application, it is shown how worst case bounds on task response time can be calculated. A general schedulability test is derived and shown to be equivalent to the tests of Harter [4] and Lehoczky et al. [7] for the case of periodic tasks and constant execution progress