操作系统单处理器调度讲述.ppt

* Traditional UNIX Scheduling Multilevel feedback using round robin within each of the priority queues If a running process does not block or complete within 1 second, it is preempted Priorities are recomputed once per second Base priority divides all processes into fixed bands of priority levels * Bands Decreasing order of priority Swapper Block I/O device control File manipulation Character I/O device control User processes * Traditional UNIX Scheduling * Uniprocessor Scheduling Chapter 9 * Aim of Scheduling Assign processes to be executed by the processor(s) Scheduling Criteria(准则) Response time(响应时间) Throughput (吞吐量) Processor efficiency * Types of Scheduling * Scheduling and Process State Transitions * Levels of Scheduling * Long-Term Scheduling Determines which programs are admitted to the system for processing Controls the degree of multiprogramming More processes, smaller percentage of time each process is executed * Medium-Term Scheduling Part of the swapping function Based on the need to manage the degree of multiprogramming * Short-Term Scheduling Known as the dispatcher Executes most frequently Invoked when an event occurs Clock interrupts I/O interrupts Operating system calls Signals * Short-Tem Scheduling Criteria User-oriented Response Time Elapsed time between the submission of a request until there is output. System-oriented Effective and efficient utilization of the processor Performance-related Quantitative Measurable such as response time and throughput * Scheduling Criteria * Scheduling Criteria (Cont.) * Queues for Scheduling * Priorities Scheduler will always choose a process of higher priority over one of lower priority Have multiple ready queues to represent each level of priority Lower-priority may suffer starvation(饥饿) Allow a process to change its priority based on its age or execution history * Priority Queuing * Decision Mode Nonpreemptive Once a process is in the running state, it will continue until it terminates or blocks itself fo