Dual-token-based fault-tolerant scheduling for hard real-time multiprocessor systems

Real time multiprocessor systems frequently assume that there exists a dedicated processor for task allocation that never fails. This assumption is, however too strong in the sense that all the physical objects are subject to failure. Moreover once the dedicated processor fails, the whole multiprocessor system will fail. As a way to solve this problem, we propose a fault tolerant scheduling algorithm based on moving dual token. While the primary processor holding a primary token performs task allocation, the backup processor holding a backup token, in case the primary processor fails, does primary processor creation. Since no dedicated processor for task allocation exists in this scheme, failure of the whole multiprocessor system due to that of the dedicated processor can be avoided. In addition, the deadline friendly scheduling policy used for backup task allocation, compared to heuristic scheduling, allows easier implementation and improved scheduling predictability. Simulation results show that the proposed dual token based algorithm yields low rejection rates over those with dedicated processor for task allocation.