第六讲 CPU的调度.ppt

第六讲 CPU的调度 Basic Concepts 基本概念 Scheduling Criteria 调度程序的评价标准 Scheduling Algorithms 调度算法 Multiple-Processor Scheduling 多处理机的调度 Real-Time Scheduling 实时调度 Algorithm Evaluation 算法评价 Basic Concepts基本概念 Maximum CPU utilization obtained with multiprogramming 进程调度的目的是要使采用多道程序设计的技术后将CPU的利用率最大化。 CPU–I/O Burst Cycle – Process execution consists of a cycle of CPU execution and I/O wait. CPU和I/O操作段的周期-进程的执行由CPU的执行和等待I/O操作的周期组成的。 CPU burst distribution 进程的调度就是如何为CPU的运行段分配资源。 Alternating Sequence of CPU And I/O Bursts Histogram of CPU-burst Times CPU SchedulerCPU调度程序 Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. 在就绪的进程中选择一个进程执行，并分配CPU CPU scheduling decisions may take place when a process:需要做CPU调度决策的时机： 1. Switches from running to waiting state. 当进程从运行状态转入等待状态时； 2. Switches from running to ready state.当进程从运行状态转入就绪状态时； 3. Switches from waiting to ready.当进程从等待状态转入就绪状态时； 4. Terminates. 进程终止时 Scheduling under 1 and 4 is nonpreemptive. 情形1和4是非抢夺的调度，其它情形是抢夺的调度 All other scheduling is preemptive. Dispatcher分派 Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; this involves:分派模块将CPU的控制权交给CPU调度程序选择的进程，分派操作的内容： switching context 上下文的切换 switching to user mode 切换到用户模式 jumping to the proper location in the user program to restart that program 跳转到用户程序的相应的位置，并启动用户程序的执行 Dispatch latency – time it takes for the dispatcher to stop one process and start another running. 分派时间-分派程序停止一个进程的执行到启动另一个进程的时间。 Scheduling Criteria进程调度的评价标准 CPU utilization – keep the CPU as busy as possible (CPU利用率-尽可能使CPU处于忙的状态) Throughput – # of processes that complete their execution per time unit(吞吐率-单位时间完成的进程数) Turnaround time – amount of time to execute a particular process(完成时间-完成一个特定的进程执行的时间) Waiting time – amount of time a process has been waiting in the ready queue(等待时间-进程在就绪队列中等待的时间) Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (f