硬实时系统中基于软件容错模型的容错调度算法

A Fault-Tolerant Scheduling Algorithm with Software Fault Tolerance in Hard Real-Time Systems

在硬实时系统中,由于任务超时完成将会导致灾难性后果,因此硬实时系统必须具有实时性和可靠性保障.软件容错模型是提高硬实时系统容错能力的一种有效方法.针对硬实时系统中容错优先级两种分配策略存在的不足,基于软件容错模型提出了一种容错优先级可提升的双重优先级分配策略.该方法通过为替代版本分配双重优先级,不仅能够提高硬实时系统的容错能力,同时还能够显著减少任务间的抢占次数.为了获得双重优先级分配的最佳策略,基于任务最坏响应时间的可调度性分析,首先提出了一种最大的双重优先级配置搜索算法(MDPCSA).然后结合MDPCSA算法,提出了一种最优的双重优先级配置搜索算法(ODPCSA).仿真实验表明,与两种分配策略相比,在提高系统容错能力和降低抢占开销方面更为有效.

Hard real-time systems are those that are specified in terms of stringent reliability and strong timing constraints owing to the fact that any failure to support correct outputs in a timely manner may result in a disaster.They are often involved in critical activities,where human lives may be at stake.These characteristics emphasize the need for making the services provided by this kind of system fault-tolerance.Software fault-tolerant model is a cost-effective means which trades the quality of computation results for promptness to tolerate the software faults.A new fault-tolerant scheduling algorithm is proposed based on the software fault-tolerant model in order to improve system fault resilience and,at the same time,reduce the preemptions.In order to achieve the optimal configuration,a maximal dual priority configuration search algorithm（MDPCSA）,which based on the worst-case response time schedulability analysis,is presented.Then,together with the MDPCSA,we propose an optimal dual priority configuration search algorithm（ODPCSA）.We show that ODPCSA is optimal in the sense that the fault resilience of task sets is maximized and the preemptions are minimized as for the proposed analysis.Compared with the related algorithms,the proposed approach is evaluated and shown to be more effective by simulation.