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Lecture Operating systems: Internals and design principles (6/E): Chapter 9 - William Stallings

Chapter 9 - Uniprocessor scheduling. This chapter begins with an examination of the three types of processor scheduling, showing how they are related. We see that long-term scheduling and mediumterm scheduling are driven primarily by performance concerns related to the degree of multiprogramming. | Chapter 9 Uniprocessor Scheduling Operating Systems: Internals and Design Principles, 6/E William Stallings Dave Bremer Otago Polytechnic, N.Z. ©2008, Prentice Hall These slides are intended to help a teacher develop a presentation. This PowerPoint covers the entire chapter and includes too many slides for a single delivery. Professors are encouraged to adapt this presentation in ways which are best suited for their students and environment. 1 Roadmap Types of Processor Scheduling Scheduling Algorithms Traditional UNIX Scheduling This chapter is concerned with scheduling on a system with a single processor. It is possible to define and clarify many design issues related to scheduling in this context. We examine the three types of processor scheduling: long term, medium term, and short term. The bulk of the chapter focuses on short-term scheduling issues. 2 Scheduling An OS must allocate resources amongst competing processes. The resource provided by a processor is execution time The . | Chapter 9 Uniprocessor Scheduling Operating Systems: Internals and Design Principles, 6/E William Stallings Dave Bremer Otago Polytechnic, N.Z. ©2008, Prentice Hall These slides are intended to help a teacher develop a presentation. This PowerPoint covers the entire chapter and includes too many slides for a single delivery. Professors are encouraged to adapt this presentation in ways which are best suited for their students and environment. 1 Roadmap Types of Processor Scheduling Scheduling Algorithms Traditional UNIX Scheduling This chapter is concerned with scheduling on a system with a single processor. It is possible to define and clarify many design issues related to scheduling in this context. We examine the three types of processor scheduling: long term, medium term, and short term. The bulk of the chapter focuses on short-term scheduling issues. 2 Scheduling An OS must allocate resources amongst competing processes. The resource provided by a processor is execution time The resource is allocated by means of a schedule An operating system must allocate computer resources among the potentially competing requirements of multiple processes. In the case of the processor, the resource to be allocated is execution time on the processor and the means of allocation is scheduling. 3 Overall Aim of Scheduling The aim of processor scheduling is to assign processes to be executed by the processor over time, in a way that meets system objectives, such as response time, throughput, and processor efficiency. Scheduling Objectives The scheduling function should Share time fairly among processes Prevent starvation of a process Use the processor efficiently Have low overhead Prioritise processes when necessary (e.g. real time deadlines) The scheduling function must be designed to satisfy a number of objectives, including fairness, lack of starvation of any particular process, efficient use of processor time, and low overhead. In addition, the scheduling function may need to