lec09-scheduling2 - Lecture 9: CPU Scheduling Chapter 5...

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Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition, Lecture 9: CPU Scheduling Chapter 5 (cont)
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5.2 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Multilevel Queue ± Ready queue is partitioned into separate queues: foreground (interactive) background (batch) ± Each queue has its own scheduling algorithm z foreground – RR z background – FCFS ± Scheduling must be done between the queues z Fixed priority scheduling; (i.e., serve all from foreground then from background). Possibility of starvation. z Time slice – each queue gets a certain amount of CPU time which it can schedule amongst its processes; i.e., 80% to foreground in RR z 20% to background in FCFS
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5.3 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Multilevel Queue Scheduling
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5.4 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Multilevel Feedback Queue ± A process can move between the various queues; aging can be implemented this way ± Multilevel-feedback-queue scheduler defined by the following parameters: z number of queues z scheduling algorithms for each queue z method used to determine when to upgrade a process z method used to determine when to demote a process z method used to determine which queue a process will enter when that process needs service
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5.5 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Example of Multilevel Feedback Queue ± Three queues: z Q 0 – RR with time quantum 8 milliseconds z Q 1 – RR time quantum 16 milliseconds z Q 2 –FCFS ± Scheduling z A new job enters queue Q 0 which is served FCFS. When it gains CPU, job receives 8 milliseconds. If it does not finish in 8 milliseconds, job is moved to queue Q 1 . z At Q 1 job is again served FCFS and receives 16 additional milliseconds. If it still does not complete, it is preempted and moved to queue Q 2 .
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5.6 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Multilevel Feedback Queues
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5.7 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition In-class Problems (1) ± What advantages does a preemptive CPU scheduling algorithm have over a non-preemptive one? ± Why do different levels of a multi-level feedback queue CPU scheduler have different time quantum? ± Some would say that round robin CPU scheduling does poorly when faced with jobs of equal length. What is their reasoning?
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5.8 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition In-class Problems (2) Assume you are given a uniprocessor system with one gigabyte of memory and a 300 gigabyte disk. The OS on the machine has a demand paged virtual
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This note was uploaded on 02/17/2012 for the course COP 6611 taught by Professor Staff during the Spring '08 term at University of South Florida - Tampa.

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lec09-scheduling2 - Lecture 9: CPU Scheduling Chapter 5...

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