Scheduling.ppt

Scheduling Key to multi-programming 多道程序设计的关键是调度 Four types of scheduling 调度有4种类型 Long term 长项调度 Medium term 中项调度 Short term 短项调度 I/O I/O调度 Scheduling Process: 进程定义 A program in execution 一个运行的程序 The “animated spirit” of a program 程序的“活灵魂” That entity to which a processor is assigned 处理器分配的实体 Long Term Scheduling Determines which programs are submitted for processing 确定哪一些程序被提交到系统处理 i.e. controls the degree of multi-programming 它控制多道程序设计的度(内存中的进程数） Once submitted, a job becomes a process for the short term scheduler 一旦提交，作业就成为进程加入到短项调度程序的队列中等待短项调度 (or it becomes a swapped out job for the medium term scheduler) 加入到中项调度程序的队列中 Long Term Scheduling Batch system 在批处理系统中 newly submitted jobs are held in a batch queue 新提交的作业保存在批处理队列中 Long term scheduler creates processes from the queue 长项调度程序从队列中选择任务为其创建进程 Criteria include priority, expected execution time, I/O requirements 选择采用的标准有：优先级、期望的执行时间和I/O需求 Long Term Scheduling Time sharing system 分时系统中 When a user attempts to connect to the system, a process request is generated 当用户希望连接系统时，产生一个进程请求 Operate system will accept all authorized comers 分时用户不是简单地排队等待，而是操作系统接收所有允许的请求 “the system is full and user should try again later” when system is saturated 当系统饱和时连接请求会遇到“系统已满和以后再试”的信息 Medium Term Scheduling Part of the swapping function (later…) 中项调度是7．3节内存管理将介绍的换入裁决的一部分 Usually based on the need to manage multi-programming 一般，换入裁决是基于多道程序“度”的管理需要 With or without virtual memory, memory management is an issue 无论有没有虚拟存储系统，存储管理都是一个重要问题， Short Term Scheduler Dispatcher （也称派遣程序） Execute frequently 执行频繁 Fine grained decisions of which job to execute next 并细粒度地判决下次执行哪个作业 i.e. which job actually gets to use the processor in the next time slot 在下一个时间片哪个作业将获得处理器的使用权 High-level scheduler 高级调度程序 Execute relatively infrequently 执行相对较少 Coarse grained decision of whether or not to take on a new process 粗粒度地决定是否接受一个新进程 Process States Pro