Module6:CPUSchedulingBasicConceptsAlternatingSequenceofCPUAndI/OBurstsHistogramofCPU-burstTimesCPUSchedulerCPUSchedulingSchemeCPUSchedulingSchemeDispatcherSchedulingCriteria(调度准则)SchedulingCriteria(调度准则)OptimizationCriteria处理机三级调度图CPU调度队列模型SchedulingAlgorithm调度算法First-Come,First-Served(FCFS)SchedulingFirst-Come,First-Served(FCFS)SchedulingFCFSScheduling(Cont.)Shortest-Job-First(SJF)SchedulingShortest-Job-First(SJF)SchedulingProcessArrivalTimeBurstTimeP10.07P22.04P34.01P45.04SJF(non-preemptive)Averagewaitingtime=(0+6+3+7)/4=4ExampleofPreemptiveSJFDeterminingLengthofNextCPUBurstExamplesofExponentialAveragingShortest-Job-First(SJF)SchedulingPrioritySchedulingPrioritySchedulingPrioritySchedulingPrioritySchedulingPrioritySchedulingRoundRobin(RR)RoundRobin(RR)Example:RRwithTimeQuantum=20HowaSmallerTimeQuantumIncreasesContextSwitchesTurnaroundTimeVariesWithTheTimeQuantumMultilevelQueueMultilevelQueueMultilevelQueueSchedulingMultilevelFeedbackQueueMultilevelFeedbackQueueMultilevelFeedbackQueuesExampleofMultilevelFeedbackQueueHighestResponseRatioNext(HRRN)高响应比优先(作业)调度算法HighestResponseRatioNext(HRRN)高响应比优先(作业)调度算法例调度图：T0123456789101112131415161718FCFSAAAABBBCCCCCDDEEEESJFAAAADDBBBEEEECCCCCRRABCDEABCDEABCEACECHRNAAAABBBDDCCCCCEEEE例解：例解-1例解-2Multiple-ProcessorSchedulingMultiple-ProcessorSchedulingReal-TimeSchedulingReal-TimeSchedulingDispatchLatencyDispatchLatencyDispatchLatencyThreadScheduling练习OperatingSystemExamplesSolarisschedulingSolaris2SchedulingWindowsXPSchedulingWindowsXPSchedulingWindowsXPPrioritiesWindowsSchedulingPrinciplesKernel:ThreadPriorityLevelsLinuxSchedulingPrioritiesandTime-slicelengthLinuxSchedulingListofTasksIndexedAccordingtoPrioritiesJavaThreadSchedulingJavaThreadScheduling(cont)Time-SlicingThreadPrioritiesAlgorithmEvaluationAlgorithmEvaluationAlgorithmEvaluationAlgorithmEvaluationEvaluationofCPUSchedulersbySimulation