Abstract:

Hard realtime systems are subject to stringent reliability and timing constraints owing to the fact that any failure to produce correct outputs in a timely manner may result in a disaster. Based on the rollback recovery model, a new faulttolerant priority assignment policy, 〖JP2〗which allows a faulty task to be carried out at higher priority levels, is proposed in order to improve system fault resilience. Furthermore, an optimal faulttolerant 〖JP〗priority configuration search algorithm (FTPCSA), which uses some properties of the schedulability analysis, is presented. It is shown that the method used to find out an appropriate faulttolerant configuration reduces the search space from O(n!) to O(n2). At last, the FTPCSA is proved to be optimal. Simulation experiment shows that this assignment policy can be used to effectively enhance the faulttolerant capability when traditional faulttolerant priority assignment policy may no longer be appropriate.