操作系统概念(英文)——5-13.ppt

October 2013 Operating System Concepts-Chapter 6 CPU Scheduling - Chapter 5CPU Scheduling An Introduction to Chapter 5 Basic issues about scheduling (§5.1) Is a scheduling algorithm good or bad ? scheduling criteria (§5.2) evaluation methods (§5.7) Several basic algorithms/mechanisms (§5.3) Scheduling in Multiple-Processor Systems (§5.4) Thread scheduling (§5.5) Case studies scheduling in modern OS (§5.6): Linux, Solaris 2 , Windows XP §5.1 Basic Concepts 5.1.1 CPU scheduling The procedure of selecting running entities in main memory ( i.e., processes or threads in the ready queue) according to some criteria, allocating CPU to the selected running entities, and then enabling them to run on CPU selecting + allocating + enabling 5.1 Basic Concepts (cont.) 5.1.2 The cycle of process execution Process execution consists of a cycle of CPU execution and I/O wait, i.e., CPU burst and I/O burst e.g. Fig.5.1 When a CPU burst occurs, the process is in the running state; When a I/O burst occurs, the process is in the waiting state CPU-burst times distribution, Fig.5.2 Fig. 5.1 Alternating Sequence of CPU And I/O Bursts Fig. 5.2 CPU burst distribution —— histogram of CPU- burst Times 5.1.2 The Cycle of Process Execution (cont.) CPU-bound process might have a few very long CPU bursts I/O-bound process might have many very short CPU bursts and some long I/O bursts. 5.1.3 Who conduct CPU Scheduling As components of OS, scheduler (§5.1.2) and dispatcher (§ 5.1.4, 分配器，调度器）are responsible for CPU scheduling The (short-term ) scheduler is responsible for CPU scheduling selects from the processes in memory that are ready to execute — on the basis of scheduling algorithms allocates the CPU to one of them /*组织和维护(就绪)进程/线程队列 The dispatcher gives control of the CPU to the process selected by the scheduler, i.e. starts the selected process: process context switching switching to user mode jumping to the proper location in the user program to res