网络与分布式系统研究室(DisNetppt课件

.,I/OManagementandDiskScheduling,Chapter11,.,CategoriesofI/ODevices,HumanreadableUsedtocommunicatewiththeuserPrintersVideodisplayterminalsDisplayKeyboardMouse,.,CategoriesofI/ODevices,MachinereadableUsedtocommunicatewithelectronicequipmentDiskandtapdrivesSensorsControllersActuators,.,CategoriesofI/ODevices,CommunicationUsedtocommunicatewithremotedevicesDigitallinedriversModems,.,DifferencesinI/ODevices,DatarateMaybedifferencesofseveralordersofmagnitudebetweenthedatatransferrates,.,DifferencesinI/ODevices,ApplicationDiskusedtostorefilesrequiresfile-managementsoftwareDiskusedtostorevirtualmemorypagesneedsspecialhardwareandsoftwaretosupportitTerminalusedbysystemadministratormayhaveahigherpriority,.,DifferencesinI/ODevices,ComplexityofcontrolUnitoftransferDatamaybetransferredasastreamofbytesforaterminalorinlargerblocksforadiskDatarepresentationEncodingschemesErrorconditionsDevicesrespondtoerrorsdifferently,.,DifferencesinI/ODevices,ProgrammedI/OProcessisbusy-waitingfortheoperationtocompleteInterrupt-drivenI/OI/OcommandisissuedProcessorcontinuesexecutinginstructionsI/Omodulesendsaninterruptwhendone,.,TechniquesforPerformingI/O,DirectMemoryAccess(DMA)DMAmodulecontrolsexchangeofdatabetweenmainmemoryandtheI/OdeviceProcessorinterruptedonlyafterentireblockhasbeentransferred,.,EvolutionoftheI/OFunction,ProcessordirectlycontrolsaperipheraldeviceControllerorI/OmoduleisaddedProcessorusesprogrammedI/OwithoutinterruptsProcessordoesnotneedtohandledetailsofexternaldevices,.,EvolutionoftheI/OFunction,ControllerorI/OmodulewithinterruptsProcessordoesnotspendtimewaitingforanI/OoperationtobeperformedDirectMemoryAccessBlocksofdataaremovedintomemorywithoutinvolvingtheprocessorProcessorinvolvedatbeginningandendonly,.,EvolutionoftheI/OFunction,I/OmoduleisaseparateprocessorI/OprocessorI/OmodulehasitsownlocalmemoryItsacomputerinitsownright,.,DirectMemoryAccess,TakescontrolofthesystemformtheCPUtotransferdatatoandfrommemoryoverthesystembusCyclestealingisusedtotransferdataonthesystembusTheinstructioncycleissuspendedsodatacanbetransferredTheCPUpausesonebuscycleNointerruptsoccurDonotsavecontext,.,DMA,.,DMA,CyclestealingcausestheCPUtoexecutemoreslowlyNumberofrequiredbusycyclescanbecutbyintegratingtheDMAandI/OfunctionsPathbetweenDMAmoduleandI/Omodulethatdoesnotincludethesystembus,.,DMA,.,DMA,.,DMA,.,OperatingSystemDesignIssues,EfficiencyMostI/OdevicesextremelyslowcomparedtomainmemoryUseofmultiprogrammingallowsforsomeprocessestobewaitingonI/OwhileanotherprocessexecutesI/OcannotkeepupwithprocessorspeedSwappingisusedtobringinadditionalReadyprocesseswhichisanI/Ooperation,.,OperatingSystemDesignIssues,GeneralityDesirabletohandleallI/OdevicesinauniformmannerHidemostofthedetailsofdeviceI/Oinlower-levelroutinessothatprocessesandupperlevelsseedevicesingeneraltermssuchasread,write,open,close,lock,unlock,.,I/OBuffering,ReasonsforbufferingProcessesmustwaitforI/OtocompletebeforeproceedingCertainpagesmustremaininmainmemoryduringI/O,.,I/OBuffering,Block-orientedInformationisstoredinfixedsizedblocksTransfersaremadeablockatatimeUsedfordisksandtapesStream-orientedTransferinformationasastreamofbytesUsedforterminals,printers,communicationports,mouse,andmostotherdevicesthatarenotsecondarystorage,.,SingleBuffer,OperatingsystemassignsabufferinmainmemoryforanI/OrequestBlock-orientedInputtransfersmadetobufferBlockmovedtouserspacewhenneededAnotherblockismovedintothebufferReadahead,.,I/OBuffering,.,SingleBuffer,Block-orientedUserprocesscanprocessoneblockofdatawhilenextblockisreadinSwappingcanoccursinceinputistakingplaceinsystemmemory,notusermemoryOperatingsystemkeepstrackofassignmentofsystembufferstouserprocesses,.,SingleBuffer,Stream-orientedUsedalineattimeUserinputfromaterminalisonelineatatimewithcarriagereturnsignalingtheendofthelineOutputtotheterminalisonelineatatime,.,DoubleBuffer,UsetwosystembuffersinsteadofoneAprocesscantransferdatatoorfromonebufferwhiletheoperatingsystememptiesorfillstheotherbuffer,.,CircularBuffer,MorethantwobuffersareusedEachindividualbufferisoneunitinacircularbufferUsedwhenI/Ooperationmustkeepupwithprocess,.,I/OBuffering,.,DiskPerformanceParameters,Toreadorwrite,thediskheadmustbepositionedatthedesiredtrackandatthebeginningofthedesiredsectorSeektimetimeittakestopositiontheheadatthedesiredtrackRotationaldelayorrotationallatencytimeitstakesforthebeginningofthesectortoreachthehead,.,TimingofaDiskI/OTransfer,.,DiskPerformanceParameters,AccesstimeSumofseektimeandrotationaldelayThetimeittakestogetinpositiontoreadorwriteDatatransferoccursasthesectormovesunderthehead,.,DiskSchedulingPolicies,SeektimeisthereasonfordifferencesinperformanceForasingledisktherewillbeanumberofI/OrequestsIfrequestsareselectedrandomly,wewillgettheworstpossibleperformance,.,DiskSchedulingPolicies,First-in,first-out(FIFO)ProcessrequestsequentiallyFairtoallprocessesApproachesrandomschedulinginperformanceiftherearemanyprocesses,.,DiskSchedulingPolicies,PriorityGoalisnottooptimizediskusebuttomeetotherobjectivesShortbatchjobsmayhavehigherpriorityProvidegoodinteractiveresponsetime,.,DiskSchedulingPolicies,Last-in,first-outGoodfortransactionprocessingsystemsThedeviceisgiventothemostrecentusersothereshouldbelittlearmmovementPossibilityofstarvationsinceajobmayneverregaintheheadoftheline,.,DiskSchedulingPolicies,ShortestServiceTimeFirstSelectthediskI/OrequestthatrequirestheleastmovementofthediskarmfromitscurrentpositionAlwayschoosetheminimumSeektime,.,DiskSchedulingPolicies,SCANArmmovesinonedirectiononly,satisfyingalloutstandingrequestsuntilitreachesthelasttrackinthatdirectionDirectionisreversed,.,DiskSchedulingPolicies,C-SCANRestrictsscanningtoonedirectiononlyWhenthelasttrackhasbeenvisitedinonedirection,thearmisreturnedtotheoppositeendofthediskandthescanbeginsagain,.,DiskSchedulingPolicies,N-step-SCANSegmentsthediskrequestqueueintosubqueuesoflengthNSubqueuesareprocessoneatatime,usingSCANNewrequestsaddedtootherqueuewhenqueueisprocessedFSCANTwoqueuesOnequeueisemptyfornewrequest,.,DiskSchedulingAlgorithms,.,RAID0(non-redundant),RAID1(mirrored),RAID2(redundancythroughHammingcode),.,RAID3(bit-interleavedparity),.,RAID4(block-levelparity),.,RAID5(block-leveldistributedparity),.,RAID6(dualredundancy),.,DiskCache,BufferinmainmemoryfordisksectorsContainsacopyofsomeofthesectorsonthedisk,.