Operating system chapter 9
اسلاید 1: 1Uniprocessor SchedulingChapter 9
اسلاید 2: 2Aim of SchedulingAssign processes to be executed by the processor(s)Response timeThroughputProcessor efficiency
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اسلاید 6: 6Long-Term SchedulingDetermines which programs are admitted to the system for processingControls the degree of multiprogrammingMore processes, smaller percentage of time each process is executed
اسلاید 7: 7Medium-Term SchedulingPart of the swapping functionBased on the need to manage the degree of multiprogramming
اسلاید 8: 8Short-Term SchedulingKnown as the dispatcherExecutes most frequentlyInvoked when an event occursClock interruptsI/O interruptsOperating system callsSignals
اسلاید 9: 9Short-Tem Scheduling CriteriaUser-orientedResponse TimeElapsed time between the submission of a request until there is output.System-orientedEffective and efficient utilization of the processor
اسلاید 10: 10Short-Term Scheduling CriteriaPerformance-relatedQuantitativeMeasurable such as response time and throughput
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اسلاید 14: 14PrioritiesScheduler will always choose a process of higher priority over one of lower priorityHave multiple ready queues to represent each level of priorityLower-priority may suffer starvationAllow a process to change its priority based on its age or execution history
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اسلاید 16: 16Decision ModeNonpreemptiveOnce a process is in the running state, it will continue until it terminates or blocks itself for I/OPreemptiveCurrently running process may be interrupted and moved to the Ready state by the operating systemAllows for better service since any one process cannot monopolize the processor for very long
اسلاید 17: 17Process Scheduling Example
اسلاید 18: 18First-Come-First-Served (FCFS)Each process joins the Ready queueWhen the current process ceases to execute, the oldest process in the Ready queue is selected
اسلاید 19: 19First-Come-First-Served (FCFS)A short process may have to wait a very long time before it can executeFavors CPU-bound processesI/O processes have to wait until CPU-bound process completes
اسلاید 20: 20Round-RobinUses preemption based on a clockAn amount of time is determined that allows each process to use the processor for that length of time
اسلاید 21: 21Round-RobinClock interrupt is generated at periodic intervalsWhen an interrupt occurs, the currently running process is placed in the read queueNext ready job is selectedKnown as time slicing
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اسلاید 24: 24Shortest Process NextNonpreemptive policyProcess with shortest expected processing time is selected nextShort process jumps ahead of longer processes
اسلاید 25: 25Shortest Process NextPredictability of longer processes is reducedIf estimated time for process not correct, the operating system may abort itPossibility of starvation for longer processes
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اسلاید 28: 28Shortest Remaining TimePreemptive version of shortest process next policyMust estimate processing time
اسلاید 29: 29Highest Response Ratio Next (HRRN)Choose next process with the greatest ratiotime spent waiting + expected service timeexpected service time
اسلاید 30: 30FeedbackPenalize jobs that have been running longerDon’t know remaining time process needs to execute
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اسلاید 40: 40Fair-Share SchedulingUser’s application runs as a collection of processes (threads)User is concerned about the performance of the applicationNeed to make scheduling decisions based on process sets
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اسلاید 42: 42Traditional UNIX SchedulingMultilevel feedback using round robin within each of the priority queuesIf a running process does not block or complete within 1 second, it is preemptedPriorities are recomputed once per secondBase priority divides all processes into fixed bands of priority levels
اسلاید 43: 43BandsDecreasing order of prioritySwapperBlock I/O device controlFile manipulationCharacter I/O device controlUser processes
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