混合关键级多任务调度中低关键级任务的积极处理

Positive handling of low-criticality tasks in mixed-criticality scheduling

当前的混合关键级多任务调度,一旦高关键级任务的执行时间需求增加,通常的做法是立即抛弃相对低关键级任务,以确保高关键级任务获得足够处理器时间。考虑到数据访问的一致性和完整性以及相应的性能损失,这种处理低关键级任务的方法过于消极;同时,任务的实际执行时间并不总是能达到最差情况下执行时间,且多处理器平台上的调度存在可观的空闲时隙。因此,完全可以也应该对低关键级任务采取更为积极的处理方法。基于同构多处理器平台,构建了两类队列,一类队列容纳回收的空闲时隙,另一类队列为任务队列,包括就绪任务队列和被抛弃的低关键级任务队列,针对这两种任务队列的特性采取不同的调度方案:就绪任务队列采用混合关键级局部调度,被抛弃的低关键级任务则对空闲时隙进行分配。仿真实验表明,此调度方法在保证高关键级任务截止时限的同时,能够使混合关键级系统的可接受任务集数目获得明显提升。

When the computation demand of （some of） the higher critical tasks increase, current mixed-criticality scheduler discards less critical tasks in order to guarantee that the higher critical tasks can occupy enough processor time for normal execution. Considering the data consistency and integrity and the corresponding performance loss, the above method for discarding the lower critical tasks arbi- trarily is very passive. On the other hand, the real computing time of tasks cannot always reach the exe- cution time under their worst case, and the scheduling has enough time slacks in multi-processors plat- form. Hence low-critical tasks should and could be handled in a more positive way. On homogenous multi-processors platform, two kinds of queues are built up. One stores the reclaimed time slacks, while the other stores tasks including the ready tasks and the discarded low critical tasks. According to the characteristics of the ready tasks and the discarded low critical tasks, two kinds of scheduling are adopt- ed= mixed-criticality local scheduling for the ready tasks, and the allocated time slacks for the discarded low critical tasks. Simulation experimental results show that, our method can guarantee the deadline of the higher critical tasks and increase acceptable ratio of tasks obviously.