操作系统Chapter09_OS调度.ppt

Uniprocessor Scheduling （调度） Chapter 9 Concepts: Assign processes to be executed by the processor(s) Response time (响应时间) To response in acceptable time Throughput （吞吐量） To improve the multi degree Processor efficiency （处理器效率） To maximize CPU utilization with multiprogramming CPU–I/O Burst Cycle: Process execution consists of a sequence of CPU execution and I/O wait. CPU burst I/O wait CPU burst I/O wait …. 9.1.2 Scheduling Types--Long-Term Scheduling （作业调度） Determines which programs are admitted to the system for processing More processes, smaller percentage of time each process is executed - Controls the degree of multiprogramming 9.1.2 Scheduling Types-- Medium-Term Scheduling Part of the swapping function Based on the need to manage the degree of multiprogramming 9.1.2 Scheduling Types--Short-Term Scheduling（低级调度，进程调度） Known as the dispatcher Executes most frequently Invoked when an event occurs Clock interrupts I/O interrupts Operating system calls Signals 9.2.1 Short-Tem Scheduling Criteria CPU utilization (使用率): keep the CPU as busy as possible. CPU throughput (吞吐量): number of processes that complete their execution per time unit. Process turnaround time (周转时间): amount of time to execute a particular process. ( Tri = tci – tsi ) Average waiting time Normalized turnaround time 归一化周转时间 9.2.1 Short-Tem Scheduling Criteria Process waiting time (等待时间): amount of time a process has been waiting in the ready queue. Process response time (响应时间): amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment). 9.2.2 Scheduling Algorithms Decision Mode Nonpreemptive Once a process is in the running state, it will continue until it terminates or blocks itself for I/O Preemptive Currently running process may be interrupted and moved to the Ready state by the operating system Allows for better servi