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ch6.ppt - Chapter 6 CPU Scheduling...

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Silberschatz, Galvin and Gagne  © 2013 Operating System Concepts – 9 th  Edition Chapter 6: CPU Scheduling
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6.2 Silberschatz, Galvin and Gagne  © 2013 Operating System Concepts – 9 th  Edition 1. Basic Concepts The objective of multiprogramming is to have some process  running at all times, to maximize CPU utilization. Scheduling of this kind is a fundamental operating-system  function. The success of CPU scheduling depends on an observed  property of processes: process execution consists of a  cycle  of  CPU execution and I/O wait.
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6.3 Silberschatz, Galvin and Gagne  © 2013 Operating System Concepts – 9 th  Edition 1.1 CPU–I/O Burst Cycle Maximum CPU utilization  obtained with multiprogramming CPU–I/O Burst Cycle – Process  execution consists of a  cycle  of  CPU execution and I/O wait CPU burst  followed by  I/O burst Processes alternate between  these two states An I/O-bound program typically  has many short CPU bursts.  A CPU-bound program might  have long CPU bursts.
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6.4 Silberschatz, Galvin and Gagne  © 2013 Operating System Concepts – 9 th  Edition 1.2 CPU Scheduler Short-term scheduler  selects from among the processes in  ready queue, and allocates the CPU to one of them The scheduler selects a process from the processes that are  ready to execute and allocates the CPU to that process.
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6.5 Silberschatz, Galvin and Gagne  © 2013 Operating System Concepts – 9 th  Edition 1.3 Preemptive Scheduling CPU scheduling decisions may take place when a process: 1. Switches from running to waiting state 2. Switches from running to ready state 3. Switches from waiting to ready 4. Terminates Scheduling under 1 and 4 is  nonpreemptive All other scheduling (2 and 3) is  preemptive
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6.6 Silberschatz, Galvin and Gagne  © 2013 Operating System Concepts – 9 th  Edition 1.4 Dispatcher Dispatcher module gives control of the CPU to the process  selected by the short-term scheduler; this involves: switching context switching to user mode Dispatch latency  – time it takes for the dispatcher to stop  one process and start another running
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6.7 Silberschatz, Galvin and Gagne  © 2013 Operating System Concepts – 9 th  Edition 2. Scheduling Criteria CPU utilization  – keep the CPU as busy as possible Throughput  – # of  processes  that complete their execution  per   time  unit Turnaround time  – amount of time to execute a particular  process Waiting time  – amount of time a process has been waiting in the  ready queue Response time  – amount of time it takes from when a request  was submitted until the first response is produced, not output  (for  time-sharing environment)
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6.8
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