Online Admission Of Non-Preemptive Aperiodic Mixed-Critical Tasks In Hierarchic Schedules

Operational safety is one of the major issues in modern industrial applications. For safety critical systems, the verification and validation efforts can be reduced using temporal isolation enforced by hierarchic schedules. In 2012, Lackorzynski et al. demonstrated that reserving bandwidth for event-triggered (ET) activities in hierarchic schedules may lead to significant bandwidth loss. In contrast to the bandwidth reservation techniques, online admission of ET activities can help reduce bandwidth losses. However, the state-of-the-art approaches for online admission of ET activities (i) cannot be utilized in hierarchic systems and (ii) incur significant scheduling overheads.In this paper, we present a flexible scheduler design for online admission of non-preemptive aperiodic tasks in a hierarchic time-triggered environment. Our approach circumvents the bandwidth loss issue in hierarchic systems, and can be implemented on top of a variety of hypervisor interfaces. In order to provide offline guarantees, we also provide a necessary test for our approach. Through evaluation, we demonstrate that our approach efficiently utilizes processor bandwidth and only incurs small overheads for a safety critical system. The experimental study also shows that our approach is comparable, in terms of execution overheads, to the state-of-the-art preemptive non-hierarchic approaches.