[工学]chap4 中断和处理机调度.ppt

4.1 中断 4.1 中断 4.1 中断 4.1 中断 4.1 中断 4.1 中断 4.1 中断 4.1 中断 4.1 中断 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 4.2 处理机调度 * 4.2.4 What is CPU scheduling? What is CPU scheduling? Determining which processes run when there are multiple runnable processes. Why is it important? Because it can have a big effect on resource utilization and the overall performance of the system. On most multitasking systems, only one process can truly be active at a time - the system must therefore share its time between the execution of many processes. This sharing is called scheduling. * 4.2.4 Scheduling Algorithms Queueing(排队)—This is appropriate for serial or batch jobs. There are two main ways of giving priority to jobs in a queue. First-Come First-Served (FCFS) , also as FIFO. Shortest Job First (SJF). Round-robin— This is the time-sharing approach in which several tasks can coexist. The scheduler gives a short time-slice(时间片) to each job round and round. These two categories are also referred to as non-preemptive and preemptive (剥夺)respectively. Strictly non-preemptive—Each program continues executing until it has finished, or until it must wait for an event (e.g. I/O or another task). Strictly preemptive —The system decides how time is to be shared between the tasks, and interrupts each process after its time-slice. It then executes another program for a fixed time and stops, then the next...etc. 4.3 实时调度 4.3 实时调度 结束时间Tc 开始时间Ts 服务时间Tr 到达时间Tin 作业 8 3 6 4 5 2 2 0 4 6 E C D A B 周转时间 T 带权周转时 间W 平均 SRT 调度算法 19 20 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 不同调度算法对同一个 作业/进程的性能比较 2.14 8.00 HRP 2 8 E 2.56 8.60 FCFS 1.84 7.60 SJF 1.59 7.20 SRT 5 6 D 4 4 C 6 2 B 3 0 A 从平均周转时间及其平均带权周转时间来看，SRT 好于前面的任何一个算法。 服务时间Tr 到达时间Tin 作业 4.2.3 调