Fault Tolerant Global Scheduling with Backup Priority Promotion

Fault tolerance is of great importance in hard real-time systems due to the impossibility of eliminating faults. In such a system the fault tolerant scheduling algorithm plays a critical role for achieving fault tolerance capability. In primary-backup scheme based fault tolerant global scheduling algorithms, the execution window of backup is relatively small. When priority inheritance strategy is adopted, the response time of the backup is likely too long to guarantee deadline requirement. For improving the real time property of the backup, we propose a fault tolerant global scheduling algorithm based on backup priority promotion strategy—FTGS-BPP. In FTGS-BPP, the backup has a higher priority than its corresponding primary so that during the execution the backup suffers less interference. Consequently the response time of the backup is reduced which means better real time performance. FTGS-BPP can achieve fault tolerance with less processors than the algorithms which follow priority inheritance strategy. A backup priority searching algorithm is also proposed. The simulation result shows that, compared with the fault tolerant global scheduling algorithm based on priority inheritance strategy, FTGS-BPP is able to reduce processor requirement significantly when scheduling the same task set.