University of Houston

We present an analytical-based approach to estimating the worst-case response time (WCRT) for a set of real-time tasks having fixed or dynamic-priorities. The analysis is an extension of the well-known worst-case response time analysis. However, the motivation for this work comes primarily from the study of the abort-and-restart (ANR) scheduling model, which is neither a concurrency control policy nor a true scheduling policy. Instead, it is a policy in which the most important tasks are scheduled first. The research addresses the specific issue of computing an upper bound to the worst-case response time of a task considering the direct interference of higher-priority tasks and the abort and restarts that they cause. An important performance aspect of the abort-and-restart scheme is that the model reduces the priority-inversion problem, but makes the reasoning of the overall system correctness more difficult. Based on analysis, in some cases the number of aborts is limited by the event set attributes or characteristics, so the handlers' response times are bounded. In other cases the number of aborts is high. There is more overhead with the abort-and-restart model, since time spent on task execution is wasted. However, the model does reduce the impact of a wrong decision. It implements executions as function evaluations. Therefore, there are no "incomplete" functions evaluations as in the case of a task's interruption. The added computational costs could be considered reasonable, given that the model offers far richer composition than traditional scheduling schemes.