The End Of The Line For Static Cyclic Scheduling?

One common way of constructing hard real-time systems is to use a number of periodic and sporadic tasks assigned static priorities and dispatched at run-time according to the preemptive priority scheduling algorithm. Most analysis for such systems attempts to find the worst-case response time for each task by assuming that the worst-case scheduling point is when all tasks in the system are released simultaneously. Often, however, a given set of hard real-time tasks will have offset constraints: a number of tasks sharing the same periodic behaviour will be constrained to execute at fixed offsets in time relative to each other. In this situation the assumption of a simultaneous release of all tasks can lead to pessimistic scheduling results. In this paper we derive good response time bounds for tasks with offset information, giving an optimal priority ordering algorithm.