36-Organization and performance of a two-level virtual-real cache hierarchy.pdf36-Organization and performance of a two-level virtual-real cache hierarchy.pdf

收藏 分享

资源预览需要最新版本的Flash Player支持。
您尚未安装或版本过低,建议您

ORGANIZATIONANDPERFORMANCEOFATWOLEVELVIRTUALREALCACHEHIERARCHYWENHANNWANG,JEANLOUPBAERANDHENRYMLEVYDEPARTMENTOFCOMPUTERSCIENCE,FR35UNIVERSITYOFWASHINGTONSEATTLE,WA98195ABSTRACTWEPROPOSEANDANALYZEATWOLEVELCACHEORGANIZATIONTHATPROVIDESHIGHMEMORYBANDWIDTHTHEFIRSTLEVELCACHEISACCESSEDDIRECTLYBYVIRTUALADDRESSESITISSMALL,FAST,AND,WITHOUTTHEBURDENOFADDRESSTRANSLATION,CANEASILYBEOPTIMIZEDTOMATCHTHEPROCESSORSPEEDTHEVIRTUALLYADDRESSEDCACHEISBACKEDUPBYALARGEPHYSICALLYADDRESSEDCACHE;THISSECONDLEVELCACHEPROVIDESAHIGHHITRATIOANDGREATLYREDUCESMEMORYTRAFFICWESHOWHOWTHESECONDLEVELCACHECANBEEASILYEXTENDEDTOSOLVETHESYNONYMPROBLEMRESULTINGFROMTHEUSEOFAVIRTUALLYADDRESSEDCACHEATTHEFIRSTLEVELMOREOVER,THESECONDLEVELCACHECANBEUSEDTOSHIELDTHEVIRTUALLYADDRESSEDFIRSTLEVELCACHEFROMIRRELEVANTCACHECOHERENCEINTERFERENCEFINALLY,SIMULATIONRESULTSSHOWTHATTHISORGANIZATIONHASAPERFORMANCEADVANTAGEOVERAHIERARCHYOFPHYSICALLYADDRESSEDCACHESINAMULTIPROCESSORENVIRONMENTKEYWORDSCACHES,VIRTUALMEMORY,MULTIPROCESSORS,MEMORYHIERARCHY,CACHECOHERENCE1INTRODUCTIONVIRTUALLYADDRESSEDCACHESAREBECOMINGCOMMONPLACEINHIGHPERFORMANCEMULTIPROCESSORSDUETOTHENEEDFORRAPIDCACHEACCESSILL,3,171AVIRTUALLYADDRESSEDCACHECANBEACCESSEDMOREQUICKLYTHANAPHYSICALLYADDRESSEDCACHEBECAUSEITDOESNOTREQUIREAPRECEDINGVIRTUALTPHYSICALADDRESSTRANSLATIONHOWEVER,VIRTUALLYADDRESSEDCACHESHAVESEVERALPROBLEMSASWELLFOREXAMPLE1THEYMUSTBECAPABLEOFHANDLINGSYNONYMS,THATIS,MULTIPLEVIRTUALADDRESSESTHATMAPTOTHESAMEPHYSICALADDRESS2WHILEADDRESSTRANSLATIONISNOTREQUIREDBEFOREAVIRTUALCACHELOOKUP,ADDRESSTRANSLATIONISSTILLNEEDEDFOLLOWINGAMISS3INAMULTIPROCESSORSYSTEM,THEUSEOFAVIRTUALLYADDRESSEDCACHEMAYCOMPLICATECACHECOHERENCEBECAUSEBUSADDRESSESAREPHYSICAL,THEREFOREAREVERSETRANSLATIONMAYBEREQUIREDPERMISSIONTOCOPYWITHOUTFEEALLORPARTOFTHISMATERIALISGRANTEDPROVIDEDTHATTHECOPIESARENOTMADEORDISTRIBUTEDFORDIRECTCOMMERCIALADVANTAGE,THEACMCOPYRIGHTNOTICEANDTHETITLEOFTHEPUBLICATIONAADITSDATEAPPEAR,ANDNOTICEISENTHATCOPY;NPISBYPERMISSIONOFTHEASSOCIATIONFORCOMPUTINGMACHINERYTOCOPYOTHERWISE,ORTOREPUBLISH,REQUIRESAFEEAND/ORSPECIFICPERMISSION4I/ODEVICESUSEPHYSICALADDRESSESASWELL,ALSOREQUIRINGREVERSETRANSLATION5AVIRTUALCACHEMAYNEEDTOBEINVALIDATEDONACONTEXTSWITCHBECAUSEVIRTUALADDRESSESAREUNIQUETOASINGLEPROCESSNONEOFTHESEPROBLEMSISINSOLVABLEBYITSELF,ANDSEVERALSCHEMESHAVEBEENPROPOSEDFORMANAGINGVIRTUALCACHESFOREXAMPLE,DUALTAGSETS,ONEVIRTUALANDONEPHYSICAL,CANBEUSEDFOREACHCACHEENTRY7,61ASANOTHEREXAMPLE,THESPURSYSTEMRESTRICTSTHEUSEOFADDRESSSPACE,PROHIBITSCACHINGOFI/OBUFFERS,ANDREQUIRESBUSTRANSMISSIONOFBOTHVIRTUALANDPHYSICALADDRESSESLLHOWEVER,THESESCHEMESTENDTOHAVEPERFORMANCESHORTCOMINGSORUNPLEASANTIMPLICATIONSFORSYSTEMSOFTWAREVIRTUALLYADDRESSEDCACHESAREFUNDAMENTALLYCOMPLICATED,ANDTHISTIMEORSPACECOMPLEXITYREDUCESTHEABILITYOFTHECACHETOMATCHTHEEVERINCREASINGNEEDSOFMODERNPROCESSORSTOATTACKTHISPROBLEM,WEPROPOSEATWOLEVELCACHEORGANIZATIONINVOLVINGAVIRTUALLYADDRESSEDFIRSTLEVELCACHEANDAPHYSICALLYADDRESSEDSECONDLEVELCACHERECENTSTUDIESOFTWOLEVELUNIPROCESSORANDMULTIPROCESSORCACHESCANBEFOUNDIN4,5,12,131THESMALLFIRSTLEVELCACHECANBEFASTTOMEETTHEREQUIREMENTSOFHIGHSPEEDPROCESSORS;ITISVIRTUALLYADDRESSEDTOAVOIDTHENEEDFORADDRESSTRANSLATIONTHELARGESECONDLEVELCACHEWILLREDUCEMISSRATIOSANDMEMORYTRAFFIC;ITISPHYSICALLYADDRESSEDTOSIMPLIFYTHEI/OANDMULTIPROCESSORCOHERENCEPROBLEMSFURTHERMORE,WESHOWHOWTHESECONDLEVELCACHECANBEUTILIZEDTOSOLVETHESYNONYMPROBLEMANDTOSHIELDTHEFIRSTLEVELCACHEFROMIRRELEVANTCACHECOHERENCETRAFFICOVERALL,WEBELIEVETHATTHISTWOLEVELVIRTUALREALORGANIZATIONRSIMPLIFIESTHEDESIGNOFTHEFIRSTLEVEL,WHEREPERFORMANCEISCRUCIAL,WHILESOLVINGSOMEOFTHEDIFFICULTPROBLEMSATTHESECONDLEVEL,WHERETIMEANDSPACEAREMOREEASILYAVAILABLEOURORGANIZATIONINVOLVESTHEUSEOFPOINTERSINTHETWOCACHESTOKEEPTRACKOFTHEMAPPINGSBETWEENVIRTUALCACHEANDPHYSICALCACHEENTRIES7WEALSOPROVIDEATRANSLATIONBUFFERATTHESECONDLEVELWHICHOPERATESINPARALLELWITHFIRSTLEVELCACHELOOKUPSINCASEAMISSREQUIRESREVERSETRANSLATIONTRACEDRIVENSIMULATIONSAREUSEDTODEMONSTRATETHEADVANTAGESOFATWOLEVELVRVIRTUALREALCACHEOVERAHIERARCHYOFREALADDRESSEDCACHESINAMULTIPROCESSORENVIRONMENTTHERESTOFTHISPAPERISORGANIZEDASFOLLOWSSECTION2DESCRIBESTHEAPPROACHESTAKENINSOLVINGVARIOUSPROBLEMSRELATEDTOVIRTUALADDRESSCACHESANDPRESENTSSOMEDESIGNCHOICESFORHIGHPERFORMANCEMULTIPROCESSORCACHESSECTION3GIVESTHESPECIFICORGANIZATIONOFAVRTWOLEVELCACHEHIERARCHYANDITSDETAILEDOPERATIONALDESCRIPTIONSECTION4PRESENTSPERFORMANCERESULTSFROMSIMULATIONS,ANDCONCLUSIONSAREDRAWNINSECTION501989ACM08847495/89/0000/014001501402DESIGNISSUESOFTWOLEVELVRCACHESFORHIGHPERFORMANCEMULTIPROCESSORSTHISSECTIONADDRESSESSOMEIMPORTANTISSUESINTHEDESIGNOFTWOLEVELVRCACHESANDMOTIVATESOURDESIGNCHOICESAMOREDETAILEDOPERATIONALDESCRIPTIONOFOURAPPROACHISGIVENINTHEFOLLOWINGSECTIONTHEPROPOSEDARCHITECTUREFORTHISEVALUATIONISASHAREDBUSMULTIPROCESSORWHEREEACHPROCESSORHASAPRIVATE,TWOLEVEL,VCACHERCACHEHIERARCHYASSHOWNINFIGURE1RCDLERCEEVCACHEVCACHEPPFIGURE1SHAREDBUSORGANIZATIONWRITEPOLICIESFORATWOLEVELCACHE,THEWRITEPOLICYCANBESELECTEDINDEPENDENTLYATEACHLEVELINTHELITERATURE,WRITETHROUGHHASBEENPROPOSEDASTHEMOSTREASONABLEWRITEPOLICYFORTHEFIRSTLEVELCACHEINATWOLEVELHIERARCHY,WHILEWRITEBACKISADVOCATEDFORTHESECONDLEVELLO,8,131AMAJORMOTIVATIONFORTHECHOICEOFWRITETHROUGHATTHEFIRSTLEVELISTHATCACHECOHERENCECONTROLISSIMPLIFIEDINTHISCASE,THEFIRSTANDSECONDLEVELCACHESWILLALWAYSCONTAINIDENTICALVALUESTHEREARESEVERALPROBLEMS,HOWEVER,WITHUSINGAFIRSTLEVELWRITETHROUGHCACHEFIRST,ASSUMINGNOWRITEALLOCATE,WRITETHROUGHCACHESWILLHAVESMALLERHITRATIOSTHANWRITEBACKCACHESSECOND,AWRITETAKESLONGERUNDERWRITETHROUGHBECAUSETHESECONDLEVELCACHEMUSTBEUPDATEDASWELL;PRIMARYMEMORYMAYALSONEEDTOBEUPDATEDDEPENDINGONTHEWRITEPOLICYFORTHESECONDLEVELTHEREDUCEDWRITELATENCYWITHWRITETHROUGHCANBEGREATLYHIDDENBYTHEUSEOFWRITEBUFFERSBETWEENTHEFIRSTANDSECONDLEVELS,BUTSEVERALWRITEBUFFERSMAYBENEEDEDTABLE1,FOREXAMPLE,SHOWSTHATINTHEEXECUTIONOFTHEVAXPROGRAMPOPSCFSECTION4,30OFWRITESAREDUETOPROCEDURECALLS,EACHOFWHICHTYPICALLYGENERATESSIXORMORESUCCESSIVEWRITESTABLE2SHOWSTHEINTERWRITEINTERVALDISTRIBUTIONFORASNAPSHOT411,237REFERENCESOFTHESAMETRACEUSINGA16KDIRECTMAPPEDCACHEWITHAMBYTEBLOCKSIZEASCANBESEEN,THEHIGHPERCENTAGEOFSHORTINTERWRITEINTERVALSCONFIRMSTHENEEDFORSEVERALBUFFERSUNFORTUNATELY,WHILEWRITEBUFFERSCANREDUCETHEWRITELATENCYOFTHEFIRSTLEVELCACHE,THEYREINTRODUCEACOMPLEXITYTHATWRITETHROUGHWASINTENDEDTOAVOID,NAMELYCACHECOHERENCEWRITEBUFFERSCANHOLDMODIFIEDDATAFORWHICHOTHERPROCESSORSMIGHTENCOUNTERAMISSTHUS,CACHECOHERENCYCONTROLMUSTBEPROVIDEDFORTHEWRITEBUFFERSONEVERYCACHECOHERENCETRANSACTIONTHESEDIFFICULTIESLEADUSTOFAVORTHEWRITEBACKPOLICYFOROURVIRTUALLYADDRESSEDCACHEATTHEFIRSTLEVELNOOFWRPERCALLCOUNTTOTALWRITES1332243004285210TABLE1NULMBEROFWRITESDUETOPROCEDMRECA116481973510ANDLARGER3245TABLE2INTERWRITEINTERVALSSNAPSHOTOF411,237REFERENCESTHESYNONYMPROBLEMASPREVIOUSLYNOTED,ATWOLEVELVRORGANIZATIONCANBEUSEDTOSOLVETHESYNONYMPROBLEMTHESOLUTIONREQUIRESTHEUSEOFAREVERSETRANSLATIONTABLE15FORDETECTINGSYNONYMS,ANDANATURALPLACETOPUTTHATTABLEISATTHESECONDLEVELOURTWOLEVELORGANIZATIONPERMITSANDDETECTSSYNONYMS,BUTGUARANTEESTHATATMOSTONECOPYOFADATAELEMENTEXISTSINTHEVCACHEATANYTIMEEACHSECONDLEVELCACHEBLOCKWILLHAVEAPOINTERTOITSFIRSTLEVELCHILDBLOCK,IFONEEXISTSIFWEGUARANTEEANINCLUSIONPROPERTY,WHERETHERCACHECONTAINSASUPERSETOFTHETAGSINTHEVCACHE,THEREVERSETRANSLATIONINFORMATIONCANBESTOREDINLOGVCACHESIZE/PAGESIZESUPERSETBITSINEACHRCACHEBLOCKFOREACHENTRYINTHERCACHEWITHACHILDINTHEVCACHE,THESEEXTRABITS,TOGETHERWITHTHEPAGEOFFSET,PROVIDETHEVCACHELOCATIONOFITSCHILDWHENAMISSOCCURSINTHEVCACHE,THEVIRTUALADDRESSISTRANSLATEDUSINGASECONDLEVELTRANSLATIONBUFFERANDTHERCACHEISACCESSEDIFANRCACHEHITOCCURS,THERCACHECHECKSWHETHERTHEDATAISALSOINTHEVCACHEUNDERANOTHERVIRTUALADDRESSASYNONYMIFSO,ITSIMPLYINVALIDATESTHATVCACHECOPYANDMOVESTHEDATATOTHENEWVIRTUALADDRESSINTHEVCACHETHUS,WHILEADATAELEMENTCANHAVESYNONYMS,ITISALWAYSSTOREDINTHEVCACHEUSINGTHELASTVIRTUALADDRESSWITHWHICHITWASACCESSED’‘NOTETHATOURAPPROACHINDEALINGWITHTHESYNONYMPROBLEMHASSOMESIMILARITIESTOGOODMAN’SAPPROACH7ONECANVIEWOURAPPROACHASMOVINGGOODMAN’SREALDIRECTORYFROMBEINGJUSTFORSNOOPINGTOBEINGASSOCIATEDWITHTHELEVELTWOCACHETHISMOVEPROVIDESTWOBENEFITSFIRST,ITHIDESTHECOSTOFGOODMAN’SEXTRA,REALDIRECTORYBYMAKINGITTHELEVELTWOCACHEDIRECTORYSECOND,ITREDUCESTHEMISSESCAUSEDBYREALADDRESSCOLLISIONSVIAMAKINGTHEREALDIRECTORYMUCHBIGGERCONTEXTSWITCHINGINAMULTIPROGRAMMINGENVIRONMENT,ADDRESSESAREUNIQUETOEACHPROCESSANDTHEREFORETHEVCACHEMUSTBEFLUSHEDWHENEVERACONTEXTSWITCHOCCURSTHISMIGHTBECOSTLYFORALARGEVIRTUALLYADDRESSEDCACHEFORSMALLCACHESWEBELIEVETHEPENALTYONHITRATIOSWILLBENEGLIGIBLEANDTHISISCONFIRMEDBYOURSIMULATIONRESULTSCFSECTION4HOWEVER,IFAWRITEBACKPOLICYISUSEDFORTHEVCACHE,ASUBSTANTIALNUMBEROFWRITEBACKSMAYOCCURATEACHCONTEXTSWITCH,WHICHGREATLYINCREASESCONTEXTSWITCHLATENCYANOTHERSOLUTIONTOAVOIDTHEADDRESSMAPPINGCONFLICTISTOATTACHAPROCESSIDENTIFIERTOEACHTAGENTRYOFTHEVCACHETHISAPPROACHDOESNOTIMPROVETHEHITRATIOFORASMALLVCACHEI,BUTCANAVOIDTHELARGENUMBEROFWRITEBACKSATCONTEXTSWITCHTIMEUNFORTUNATELY,THISAPPROACHINCREASESTHECOMPLEXITYOFATWOLEVELHIERARCHYBECAUSETHEVCACHENEEDSTOBEPURGEDORSELECTIVELYFLUSHEDWHENATLBENTRYOFANINACTIVEPROCESSISREPLACEDBYANENTRYOFTHEACTIVEPROCESS,ORAPROCESSIDISREASSIGNEDWEWISHTOHAVETHEBENEFITSOFREDNCEDCONTEXTSWITCHLATENCYWITHOUTNEEDINGTOFLUSHTHEVCACHEWHENATLBENTRYCHANGESOURAPPROACHMEETSTHESEGOALSBYINVALIDATINGALLVCACHEBLOCKSONACONTEXTSWITCHBUTNOTWRITINGTHEMBACKATTHATTIMEINSTEAD,EACHBLOCKISWRITTENBACKONLYWHENITISREPLACED,THATIS,WHENANEWBLOCKISREADINTOTHATCACHESLOTTHEWRITESARETHUSDISTRIBUTEDINTIMEWHERETHELATENCYCANBEHIDDENUSINGWRITEBACKBUFFERSTOIMPLEMENTTHISSCHEME,WEADDTWONEWFIELDSTOEACHVCACHEBLOCKFIRST,WEADDASWAPPEDVALIDBIT,WHICHISSETFOREACHVCACHEBLOCKONACONTEXTSWITCHUPONAREPLACEMENT,IFTHEVCACHEFINDSABLOCKWITHSWAPPEDVALIDSET,ITCHECKSWHETHERTHATBLOCKISALSOMARKEDBOTHDIRTYANDVALID;IFSO,THATBLOCKMUSTBEWRITTENBACKSECOND,WEADDANRPOINTER,WHICHISTHELOWORDERBITSOFTHEPAGENUMBER,TOEACHVCACHEBLOCKTHERPOINTER,TOGETHERWITHTHEPAGEOFFSET,ISSUFFICIENTTOLINKAVCACHEENTRYTOITSCORRESPONDINGLOCATIONINTHERCACHETHISLINKAGEMAKESAWRITEBACKORASTATECHECKEFFICIENT,SINCETHEREISNONEEDFORANADD
编号:201401051948256813    类型:共享资源    大小:985.98KB    格式:PDF    上传时间:2014-01-05
  
5
关 键 词:
工业、机械、能源、设计、建模、模具、工学
  人人文库网所有资源均是用户自行上传分享,仅供网友学习交流,未经上传用户书面授权,请勿作他用。
关于本文
本文标题:36-Organization and performance of a two-level virtual-real cache hierarchy.pdf
链接地址:http://www.renrendoc.com/p-256813.html

当前资源信息

4.0
 
(2人评价)
浏览:37次
baixue100上传于2014-01-05

官方联系方式

客服手机:17625900360   
2:不支持迅雷下载,请使用浏览器下载   
3:不支持QQ浏览器下载,请用其他浏览器   
4:下载后的文档和图纸-无水印   
5:文档经过压缩,下载后原文更清晰   

精品推荐

相关阅读

人人文库
关于我们 - 网站声明 - 网站地图 - 资源地图 - 友情链接 - 网站客服客服 - 联系我们

网站客服QQ:2846424093    人人文库上传用户QQ群:460291265   

[email protected] 2016-2018  renrendoc.com 网站版权所有   南天在线技术支持

经营许可证编号:苏ICP备12009002号-5