文献翻译功耗优化从超低功耗到耗电系统.docx

文献翻译功耗优化从超低功耗到耗电系统.docx

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文献翻译功耗优化从超低功耗到耗电系统

本科毕业设计

外文文献及译文

文献、资料题目：

POWEROPTIMIZATIONS

文献、资料来源：

期刊

文献、资料发表（出版）日期：

2006.3.25

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专业：

班级：

姓名：

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翻译日期：

外文文献：

POWEROPTIMIZATIONS:

FROMULTRA-LOWPOWERTOPOWER-HUNGRYSYSTEMS

Inthissection,weprovideanoverviewofpoweroptimizationstargetedatfourtypesofsystems:

Energy-scavengingultralowpowersystems,batteryoperatedembeddedandmobilesystems,plugged-indesktopmachinesandhigh-endservers.Whilesomeoftheoptimizationsareusefulacrossthedifferentcategoriesofsystems,domain-specificpoweroptimizationsareeffectiveinbalancingtheoftenconflictingdesignconstraints.Becauseprototypehardwarecanbeexpensivetodevelop,researchanddevelopmentinpower-awaredesigntypicallyrequiressimulation.Dependingonthetechnique,thismayrequireanythingfromdetailedcircuitsimulations,tocycle-by-cyclepipelinesimulations,tocoarse-grained,event-drivensystem-eventsimulations.

UltraLowPowerSystems

Theneedforultra-lowpowerdeviceshasemergedinvariousapplicationssuchasunmonitoredsensornetworksandmedicalprosthetics,wheretheamountofenergythatcanbetransferredtotheimplanteddevicefromanexternalpowersourceislimited.Insuchultra-lowpowerdevices,energymustoftenbescavengedfromtheenvironmentviathermalormechanicalmeanssimilartoold-fashionedself-windingwatches.Theamountofpoweravailableinthiswayissolowthat,inadditiontotheneedforlowdynamicenergyconsumptionduringoperationalphase,itisimperativethatthestaticpowerconsumptioninidlestateisalsonegligible.Ifthisconditionisnotmet,mostofenergyscavengedwillbewastedinstaticpowerdissipationandtherewillbeinsufficientenergytosustainthedeviceoperation.Consequently,ultra-lowpowerdevicesneedtodeployintelligentstrategiestoshutdowncomponentsorportionsofthesystemintolowerstaticpowermodestoconservepowerconsumption.Forexample,[F11]presentsamultiplierdesignthatcandynamicallyshutdownportionsofthecomponentbasedonthebitwidthoftheoperands.Itisalsopossibletoreducesamplingratesofanalogtodigitalconvertersorreducetheirprecisiontoreducepowerconsumptionbasedonqualityofservicerequirements.Significantpowerreductionisalsopossiblebycustomizingthecomponentsforthetargetedapplication.Forexample,anarchitectureforanevent-drivensensorapplicationwithhardwaresupportforinterruptprocessingcanbemorepowerefficientthanasimplemicrocontrollerthatreliesonoperatingsystemkernelsforhandlinginterrupts.Further,hardwareaccelerationblockscanbeusedforcommonsensoroperationssuchaspacketprocessingandforwardingtoimproveperformanceandreducepowerconsumption.Inadditiontocomputationalblocks,memoryorganizationcanalsobecustomized,asillustratedin[F11].

Inmanyoftheultra-lowpowersensingapplications,theperformancerequirementsarequitemodestincomparisontodesktopmachines.IncontrasttothefewGHzclockfrequenciesdeployedindesktopprocessors,thesesystemscanmeetfunctionalrequirementswhileoperatingatspeedsintherangeofafewKHz.Thislowspeedrequirementmakesitpossibletousearchitecturesbasedonsub-thresholdcircuits.Insuchsystems,thecircuitsuseleakagecurrentstochargeanddischargeloadcapacitancesanddramaticallyreduceoverallpowerconsumptionatexpenseofslowoperatingspeeds.Findinganoptimalvoltagetooperatethesystemshouldstrikeabalancebetweentheadditionalstaticpowerconsumedduetothesloweroperatingsystemwiththequadraticpowersavingsduetosupplyvoltagereduction.Inaddition,thedesignofsub-thresholdarchitecturesposevariouschallengesastheyaremoresusceptibletoexternalnoisesuchassofterrorsandaremoreinfluencedbyprocessvariation.

EmbeddedandMobileSystems

Thenextclassofdevicesisthebattery-operatedlowpowerembeddedandmobiledevicesthatcanberechargedorreplacedperiodically.Thesedevicesneedtoprolongbatterylifewhilemeetingotherconstraintssuchassystemcostandqualityofservicerequirements.Someoftheembeddedsystemstradeoffqualityofservicewiththepowerconsumed.Forexample,portablevideoplayerscanreducethevideoqualityorsizeforreducingpowerconsumption.Sincemanyembeddedsystemsaredrivenbyaconstantthroughputrequirementratherthanoverallcomputationtime,itispossibletoexploitthevariabilityinworkloadstoreducepowerconsumption.Forexample,thecharacteristicsofavideostreamthatcanbedecodedbythevideoplayerataratefasterthan30fpscanbeusedtoreducesupplyvoltageorincreasethresholdvoltage.Whilepipeliningandparallelismhavebeenusedinhigh-performancedomainsforimprovingperformance,theycanbeusedforreducingpowerinconstantthroughputapplications,Theadditionalslackobtainedthroughreducedlogicdepthusingdeeperpipeliningcanbeexploitedbyreducingsupplyvoltageinsteadofreducingthefrequency.Theoptimaldepthofpipeliningforpowerconsumptiondependsonvariousfactorssuchasoverheadsofpipelineregister,activityfactorofthecircuit,theclockgatingmechanismusedtoreduceactivityinthepipelineregistersandtheratiobetweenleakageanddynamicenergy.Aparallelarchitecturecanbeusedsimilarlytoreducepowerbyoperatingmultipleinstancesatlowervoltagesinsteadofoperatingasingleunitfasterusingahighersupplyvoltage

Theutilizationofthesystemcomponentsvariesbasedontheapplicationworkload.Consequently,mostcomponentsofembeddedsystemssupportmultiplepowermodes.Typicallyamodewithlowerpowerconsumptionalsoincursmoreperformancepenalty.Forexample,aCPUoperatingatalowervoltagerequiresalongercycletime.Themodetransitionpoliciescanbeimplementedeitherdirectlyinhardware,orwhenmoreflexibilityisrequired,insoftware.Batteryoperatedsystemsalsorelyonimprovingthesynergybetweenthesoftwareandthehardwarecharacteristicsforprolongingbatterylife.Exampleoptimizationsincludeshapingthecurrentdrawnbythesystemtomaximizethebatteryefficiencyandchangingmemorydataaccesspatternsforplacingmorememorymodulesinlowerpowermodes.Similartoultra-lowpowersystems,embeddedsystemsalsorelyonhardwareaccelerationforcommonlyexecutedtaskstoreducepowerconsumption.Forexample,mostportableMPEGplayersincludeanASICfordedicated,efficientMPEGdecoding.Sincemanyembeddedapplicationsexecuteaknownsetofapplications,useofdeterministicsoftware-managedcaches（scratchpadmemories）ispreferredtotraditionalhardwaremanagedcachestoobtainbestperformanceandconsequent,energysavings.

DesktopSystems

Desktopsystemshavetraditionallyfocusedonperformanceasthemaindesignmetric.Consequently,numerousenhancementsforperformanceimprovementhavebeendeveloped,butsometimesatthecostofincreasedpower.Techniquessuchasbranchprediction,valueprediction,pre-fetchingandpredicationhavethepotentialtoimproveexecutiontime,reducingenergypertask,butontheotherhandmayincreasetheamountofwastedenergyduetoexecutionofinstructionsinthewrongpathduetomis-speculationorpre-fetchingblocksthatwillneverbeused.Theaggressivenessofthesetechniquesmustbebalancedagainsttheirpotentialwastefulness.Runtimefeedback-directedtechniquesarealsopossible,butrobust,stablecontrolschemesarenotyetavailable.

Superscalarprocessorsusedinworkstationsandpersonaldesktopsystems（includinghigh-performancelaptops）alsoprovidemanyopportunitiesforruntimeadaptationtoworkloadcharacteristics.[F10]providesasurveyofsomeofthesetechniques.Coarse-grainedadaptation,intheformofDVFSandsleepmodes,isalreadyavailableinmanypersonalcomputers,aswellasserversystems,andisgovernedbytheACPIstandard（AdvancedConfigurationandPowerInterface）.Finer-grainadaptationispossibleaswell.Thesizeandcomplexityofmanymicroarchitecturalcomponentssuchastheissuequeue,registerfile,cachesandfunctionalunitsareusuallydesignedtoaccommodateburstsofactivity,butcanoftenbereducedbasedontheirpredictedusageoroccupancy.Asmallerstructurehelpsreducethedynamicenergyduetoasmallerloadcapacitanceandalsoreduceleakageenergyasfewertransistorsareleaking.Breakinglargeorheavilymulti-portedstructuresintodecoupledclusterscanalsohelpreducedynamicenergyaswellaspossiblyimprovingaccesslatency.Dynamicadaptationtechniquesneedtocarefullyevaluatetheoverheadforsupportingadaptationandtheresultinginfluenceonthepowerconsumptionoftherestofthecomponents.Furtherdynamicadaptationtechniquescanreducecostbypermittingthethermalandcoolingmechanismstobedesignedbasedontheaveragecasebehavior.Forexample,on-chipthermalsensorscantriggerpowerreductiontechniquessuchasinstructionthrottlingandvoltagescalingwhenthechiptemperatureincreasesbeyondaspecifiedcriticallevel.

High-EndServers

Incontrasttotheultra-low-power,battery-operateddevicesthatexhibitlongsleeptimesinterspersedwithsparseactivecomputationmodes,serversystemsarepluggedin,usuallyconsistofamultitudeofcomponentsystems,altogetherconsistingofamultitudeofCPUs,disks,memory,board-levelandsystem-levelinterconnectandrouters,etc.,andcansustainprolongedburstsofactivity.Thismeansthatserversystemsareoftenprovisionedforpeakload.Burstscanoccurunexpectedly（consideranewssiteaftersomemajorevent）,butkeepingtheentireserverclusteratfullpowerisunacceptable.Electricutilitycostsinadatacenter（includingc