Breaking of Cyclic Dependencies by Scheduling for Scalable and Accurate Network Calculus Analysis

Interconnected hard real-time systems require worst-case bounds on their communication to guarantee for correct behavior. Formal derivation of such bounds is a difficult task by itself, yet, certain system characteristics are known to pose further challenges. One of these is the presence of cyclic dependencies as – in the worst-case modeling of formal verification techniques – data flows may mutually deprive each other of any remaining data forwarding service. Network Calculus (NC) is one of the formal techniques for delay bounding. On the one hand, it offers analyses that closely model system behavior, yet often restricted to networks without cyclic dependencies. On the other hand, it offers analyses that can bound delays in case of cyclic dependencies, but suffers from untight worst-case system modeling. A recent idea is to leverage scheduling capabilities. That is, separately allocating resources at locations of interference such that cyclic dependencies are broken. Previous fundamental work was able to illustrate the beneficial applicability of this idea to ring network topologies, leaving the question of generalizability open. In this paper, we provide algorithms to generalize to generic networks and explore the tradeoff between quality and cost of breaking cycles by scheduling.