Mixed-criticality Scheduling with Dynamic Memory Bandwidth Regulation

Mixed-criticality multicore system design must often provide both safety guarantees and high performance. Memory bandwidth regulation among different cores can be a useful tool for providing safety guarantees as it mitigates the interference when accessing main memory. The use of mode changes and system models such as those of Vestal can help provide both safety, for critical functions, and scheduling performance, by efficiently utilising the platform. In this work, we therefore combine per-core memory access regulation with the well established Vestal model and improve on the state-of-the-art in two respects. 1) we allow the memory access budgets of the cores to be dynamically adjusted, when the system undergoes a mode change, reflecting the different needs in each mode, for better schedulability. 2) we devise a memory-regulation-aware and stall-aware schedulability analysis for such systems, based on the well-known AMC-max technique. By comparison, the state-of-the-art did not offer the option of dynamic adjustment of core budgets, and only offered regulation-aware schedulability analysis based on AMC-rtb, which is inherently more pessimistic. As an additional contribution, 3) we consider different task assignment and bandwidth allocation heuristics, in experiments with synthetic task sets, to assess the improvement from using dynamic memory budgets and the new analysis. In our results, we have observed an improvement in schedulability ratio up to 9.1% over the state-of-the-art algorithm.