Multi-layer Bus Optimization for Real-Time Task Scheduling with Chain-Based Precedence Constraints

One major challenging issue in the designs of multi-core embedded systems is to tackle the communication problem among tasks with performance requirements and precedence constraints. This paper targets the problem of scheduling real-time tasks with chain-based precedence constraints over multi-layer bus systems with an objective to minimize the bus cost. We show the NP-hardness of the problem and the best possible approximation ratio of approximation algorithms. A polynomial-time optimal algorithm is first proposed for a restricted case in which one multi-layer bus and unit execution and communication times are considered. The result is then extended as a pseudo-polynomial-time optimal algorithm in the considerations of multiple multi-layer buses and arbitrary execution and communication times. The capability of the proposed algorithm was evaluated to provide more insights in system designs, compared to some popular heuristics.