Chapter 4 - Scheduling. Scheduling is the act of selecting the next process to be serviced by a CPU. This chapter discusses how a scheduler uses the fundamental techniques of prioritybased scheduling, reordering of requests, and variation of time slice to achieve a suitable combination of user service, efficient use of resources, and system performance. It describes different scheduling policies and their properties. | PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this PowerPoint slide may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this PowerPoint slide, you are using it without permission. Scheduling Scheduling is the act of determining the order in which requests should be taken up for servicing A request is a unit of computational work It could be a job, a process, or a subrequest made to a process Scheduling related concepts and terms Request related concepts and terms Arrival time Request is submitted to the system Admission time Kernel starts considering the request for scheduling Completion time Deadline Time by which servicing of a request should be completed Service time Total of CPU time and I/O time . | PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this PowerPoint slide may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this PowerPoint slide, you are using it without permission. Scheduling Scheduling is the act of determining the order in which requests should be taken up for servicing A request is a unit of computational work It could be a job, a process, or a subrequest made to a process Scheduling related concepts and terms Request related concepts and terms Arrival time Request is submitted to the system Admission time Kernel starts considering the request for scheduling Completion time Deadline Time by which servicing of a request should be completed Service time Total of CPU time and I/O time required to service a request Preemption Priority A schematic of scheduling Admission of an arrived request may be delayed for reasons seen later An admitted request remains pending until it is scheduled A preempted request is put back into the pool of pending requests Performance related concepts and terms User service related concepts and terms Response time Turn-around time Weighted turn-around = Turn-around time / service time Deadline overrun Amount of time by which a deadline is missed Fair share A specified share of CPU time that should be devoted to a process or a group of processes Response ratio Response ratio = (time since arrival + service time) / service time Performance related concepts and terms We shall use the following terms Terms related to average service Mean response time Mean turn-around time Terms related to scheduling performance Schedule length The total amount of time required to service a set of requests Throughput Number of requests serviced per unit of time .
