两种改进的EDF软实时动态调度算法  

Two Improved EDF Dynamic Scheduling Algorithms in Soft Real-Time Systems

作　　者：李琦[1] 巴巍 

机构地区：[1]大连理工大学电子与信息工程学院,辽宁大连116024 [2]大连测控技术研究所,辽宁大连116013

出　　处：《计算机学报》2011年第5期943-950,共8页Chinese Journal of Computers

基　　金：中央高校基本科研业务费专项基金(1300852007)资助

摘　　要：软实时系统中,任务的随意抢占浪费了CPU资源,过多的任务丢失降低了系统的调度性能.文章引入"动态模糊阈值"概念,提出了两种新的类似EDF调度的模糊阈值调度算法.两种算法在任务执行过程中,分别通过缩短和延长当前任务截止期至动态模糊阈值的方法节约资源、提高任务完成率.给出模糊阈值的临界值计算公式,分析算法的可调度性,进行仿真与性能分析比较.结果表明,与EDF调度算法比较,两种算法有效地提高了重要任务的完成率,当截止期被延长时,任务的错失率明显降低,当截止期被缩短时,任务间的切换次数大大减少.因此,新算法提高了CPU的利用率,改善了系统的实时性能.In soft real-time systems,the CPU resource is wasted by switching optionally and the schedulability of the system is decreased by the losing of overmany tasks.The concept of dynamic fuzzy threshold is introduced in this paper,based on which two improved EDF scheduling algorithms are proposed.The deadline of the executing task is delayed to save the resource in one algorithm and is shorten to increase the ratio of success in the other.In this paper,the formulae of the critical value for fuzzy threshold are given and the schedulability is discussed.Finally,the performance of the algorithms is experimentally examined and compared with the EDF algorithm in detail.Results show that,the ratio of success for important tasks is increased efficiently by using these two methods.The missed deadline percentage is decreased obviously while the deadline is delayed and the switching number is reduced greatly while the deadline is shorten.Therefore,by using the new algorithms,the ratio of CPU utilization is enhanced and the real-time capability of the system is improved.

关 键 词：EDF 抢占阈值 语言模糊集 模糊规则 

分 类 号：TP316[自动化与计算机技术—计算机软件与理论]