截止时限为关键参数的混合关键级实时任务调度研究

混合关键级系统 (mixed criticality system)的研究源于在单一平台上执行多个重要级不同的功能,当前混合关键级调度研究，一般考虑高关键级任务在不同关键级运行模式表现为或周期或计算时间不同，即以任务释放时间间隔和最差情况执行时间为关键参数.但截至时限(dendline)也是实时任务的重要时间参数，尤其是对硬实时任务，以截止时限作为关键参数进行相应混合关键级调度的研究尚是空白.针对此问题，以截止时限作为关键参数，以响应时间分析为基础，对单处理器平台中的混和关键级任务的可调度性进行分析，并提出了一种预提升关键级的调度算法RCLA(raising critical-level in advance)，在低关键级运行模式下，高关键级低优先级任务有限度地提前抢占低关键级高优先级任务的执行，既确保了满足高关键级任务在不同关键级运行模式下的截止时限，也让尽可能多的任务可以被调度执行，使得计算资源得以充分利用.仿真结果验证了RCLA算法的有效性.

Scheduling of Mixed Criticality Real-Time Tasks Set with Deadline as the Critical Parameter

An increasing trend in real-time systems is to integrate multiple functionalities of different levels of criticality, or importance, on the same platform, which leads the research of mixed criticality systems. In the current mixed criticality scheduling research, worst-case execution times or periods of high critical-level tasks are critical parameters, which are different between in high-critical mode and low-critical mode. Deadline is also an important time-parameter, especially in hard real-time systems, whereas how to schedule mixed criticality tasks using deadline as the critical parameter is still lack of discussion. This paper considers the mixed criticality scheduling in which deadlines of tasks are the critical parameter on a uniprocessor platform. Towards satisfying schedulability of high-criticality tasks in both modes, we use response time analysis to get timing-demand of fixed priority tasks and propose the raising critical-level in advance (RCLA) scheduling algorithm. RCLA gets high-critical tasks with lower priority to preempt low-critical tasks with higher priority earlier and limitedly. As well as meeting the deadlines of high criticality tasks in high-criticality mode and low-criticality mode, RCLA can schedule mixed criticality tasks as many as possible. Simulation results illustrate the benefits of this scheme.