普通本科专业毕业论文(设计)

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1、SchedulingAlgorithmicResearchRamiAbielmona94.571(ELG6171)MondayMarch27,2000Prof.T.W.PearceSchedulingAlgorithmsIntroductionProblemdefinition:“OneCPUwithanumberofprocesses.OnlyoneprocesscanusetheCPUatatimeandeachprocessisspecializedinone,andonetask.What’sthebestwaytoorganizetheprocess

2、es(schedulethem)?”[1]“HowwilltheCPUtimebedividedamongtheprocessesandthreadscompetingtouseit?”[2]SchedulingAlgorithmsEmbeddedOSArchitectureKernel:TheexecutorExecutive:ThemanagerApplicationPrograms:TheprogrammertasksRealWorldInterfacing:S/WhandlingtheH/WSchedulingAlgorithmsBasicAssu

3、mptionsApoolofrunnableprocessesarecontendingforoneCPU;Theprocessesareindependentandcompeteforresources;ThejobofthescheduleristodistributethescarceresourceoftheCPUtothedifferentprocesses“fairly”andinanoptimalway;Thejobofthedispatcheristoprovidethemechanismforrunningtheprocesses;TheOS

4、isamultitasking,butnotamultiprocessor,one;OnlyCPUschedulingisconsidered(thelowestlevelofscheduling).SchedulingAlgorithmsEvaluationCharacteristicsSchedulingAlgorithmsProcessesandResourcesResources:Preemptible:Takeresourceaway,useitforsomethingelse,thengiveitback.(e.g.processororI/O

5、channel)Non-preemptible:Oncegive,itcan’tbereuseduntilprocessgivesitback.(e.g.filespaceorterminal)Processes:IObound:PerformlotsofIOoperations.IOburst----shortCPUbursttoprocessIO---IOburstCPUbound:PerformlotsofcomputationanddolittleIOCPUburst-----------SmallIOburst-----------CPUburstS

6、chedulingAlgorithmsProcessStateTransitionsThestatesofaprocess,atanygiventime,iscomprisedofthefollowingminimalset:Running:TheCPUiscurrentlyexecutingthecodebelongingtotheprocess.Ready:Theprocesscouldberunning,butanotherprocesshastheCPU.Waiting:Beforetheprocesscanrun,someexternalevent

7、mustoccur.SchedulingAlgorithmsTypesofSchedulersLong-termscheduler:admitsnewprocessestothesystem;requiredbecauseeachprocessneedsaportionoftheavailablememoryforitscodeanddata.Medium-termscheduler:isnotfoundinallsystems;requiredtocontrolthetemporaryremovalfrommemoryofaprocesswhenthela

8、tterisextractable.S