05-CPU_Scheduling_I_2spp

05-CPU_Scheduling_I_2spp - 1 CSE 421/521 - Operating...

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Unformatted text preview: 1 CSE 421/521 - Operating Systems Fall 2011 Tevfik Ko ar University at Buffalo September 13 th , 2011 Lecture - V CPU Scheduling - I 2 Roadmap CPU Scheduling Basic Concepts Scheduling Criteria & Metrics Different Scheduling Algorithms FCFS SJF Priority RR 3 Basic Concepts Multiprogramming is needed for efficient CPU utilization CPU Scheduling: deciding which processes to execute when Process execution begins with a CPU burst , followed by an I/O burst CPUI/O Burst Cycle Process execution consists of a cycle of CPU execution and I/O wait 4 Alternating Sequence of CPU And I/O Bursts 5 Histogram of CPU-burst Durations 6 Process State As a process executes, it changes state new : The process is being created ready : The process is waiting to be assigned to a process running : Instructions are being executed waiting : The process is waiting for some event to occur terminated : The process has finished execution 7 CPU Scheduler Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them ! short-term scheduler 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 5. A new process arrives Scheduling under 1 and 4 is nonpreemptive/cooperative Once a process gets the CPU, keeps it until termination/switching to waiting state/release of the CPU All other scheduling is preemptive Most OS use this Cost associated with access to shared data i.e. time quota expires 8 Dispatcher Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; Its function involves: switching context switching to user mode jumping to the proper location in the user program to restart that program Dispatch latency time it takes for the dispatcher to stop one process and start another running 9 Scheduling Criteria CPU utilization keep the CPU as busy as possible --> maximize Throughput # of processes that complete their execution per time unit --> maximize Turnaround time amount of time passed to finish...
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05-CPU_Scheduling_I_2spp - 1 CSE 421/521 - Operating...

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