Flow-Based Mode Changes: Towards Virtual Uniprocessor Models for Efficient Reduction-Based Schedulability Analysis of Distributed Systems

This paper is the first to consider new uniprocessor task models motivated by the needs of reduction-based schedulability analysis techniques for distributed systems. Reduction-based analysis is a recent category of distributed system schedulability analysis techniques that reduces distributed real-time workloads to equivalent virtual uniprocessor ones for purposes of analysis using classical uniprocessor techniques. The approach motivates research on uniprocessor task models that better match the peculiarities of task loads reduced from distributed systems. We show that previous reduction-based schedulability analysis techniques suffer from pessimism that results from mismatches between uniprocessor analysis assumptions and characteristics of workloads reduced from distributed systems. To address the problem, we introduce flow-based mode changes, a uniprocessor load model tuned to the novel constraints of workloads reduced from distributed system tasks. Reducing distributed workload to this model, our simulation studies suggest that the resulting schedulability analysis is able to admit over 25% more utilization than other existing techniques, while still guaranteeing that all end-to-end deadlines of tasks are met.