Chapter 9 - M09_STAL6329_06_SE_C09.QXD 2/21/08 9:32 PM Page...

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P ART F OUR A n 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.The scheduling function must be designed to satis- fy 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 take into account different levels of priority or real-time dead- lines for the start or completion of certain processes. Over the years, scheduling has been the focus of intensive research, and many different algorithms have been implemented.Today, the emphasis in scheduling re- search is on exploiting multiprocessor systems, particularly for multithreaded appli- cations, and real-time scheduling. ROAD MAP FOR PART FOUR Chapter 9 Uniprocessor Scheduling Chapter 9 concerns scheduling on a system with a single processor.In this limited con- text,it is possible to define and clarify many design issues related to scheduling.Chap- ter 9 begins with an examination of the three types of processor scheduling:long term, medium term, and short term.The bulk of the chapter focuses on short-term schedul- ing issues. The various algorithms that have been tried are examined and compared. Chapter 10 Multiprocessor and Real-Time Scheduling Chapter 10 looks at two areas that are the focus of contemporary scheduling research. The presence of multiple processors complicates the scheduling decision and opens up new opportunities. In particular, with multiple processors it is possible simultaneously to schedule for execution multiple threads within the same process. The first part of Chapter 10 provides a survey of multiprocessor and multithreaded scheduling. The remainder of the chapter deals with real-time scheduling. Real-time requirements are the most demanding for a scheduler to meet,because requirements go beyond fairness or priority by specifying time limits for the start or finish of given tasks or processes. Scheduling 404 M09_STAL6329_06_SE_C09.QXD 2/21/08 9:32 PM Page 404
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U NIPROCESSOR S CHEDULING 9.1 Types of Professor Scheduling Long-Term Scheduling Medium-Term Scheduling Short-Term Scheduling 9.2 Scheduling Algorithms Short-Term Scheduling Criteria The Use of Priorities Alternative Scheduling Policies Performance Comparison Fair-Share Scheduling 9.3 Traditional UNIX Scheduling 9.4 Summary 9.5 Recommended Reading 9.6 Key Terms, Review Questions, and Problems APPENDIX 9A Response Time APPENDIX 9B Queuing Systems Why Queuing Analysis? The Single-Server Queue The Multiserver Queue Poisson Arrival Rate CHAPTER 405 M09_STAL6329_06_SE_C09.QXD 2/21/08 9:32 PM Page 405
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406 CHAPTER 9 / UNIPROCESSOR SCHEDULING In a multiprogramming system,multiple processes exist concurrently in main memory.
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This note was uploaded on 02/10/2010 for the course EXTC 56 taught by Professor Stalling during the Spring '10 term at Abu Dhabi University.

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Chapter 9 - M09_STAL6329_06_SE_C09.QXD 2/21/08 9:32 PM Page...

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