Service guarantee exploration for mixed-criticality systems

Most mixed-criticality scheduling algorithms have the problem of service interruption for low-critical tasks, which has prompted several recent studies on providing various service guarantees for such tasks. In this paper, focusing on dual-criticality systems, we explore the best achievable service guarantees for low-critical tasks in different running modes and investigate their trade-offs. Specifically, the Elastic Mixed-Criticality (E-MC) task model is first extended to allow each low-critical task to have a pair of small and large periods, which represent its service guarantees in the low and high running modes, respectively. To improve system schedulability under a mode-switch EDF scheduler, virtual deadlines for high-critical tasks are also incorporated. Then, we develop new demand bound functions (DBFs) following a unified approach and analyze the corresponding schedulability conditions. The service guarantees for low-critical tasks are explored via the adjustment of their paired periods. We show that, compared to the state-of-the-art solution, the proposed schedulability test derived from the refined DBFs can accommodate smaller periods and thus achieve better service guarantees for low-critical tasks. Moreover, there are some interesting trade-offs between the service guarantees and a few guidelines are attained for properly specifying them.