Mechanical Sympathy_ False Sharing.pdf

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1、13-6-14MechanicalSympathy:FalseSharing分享19更多下一個網誌»建立網誌登入MechanicalSympathyHardwareandsoftwareworkingtogetherinharmonySaturday,30July2011SearchThisBlogFalseSharingSearchMemoryisstoredwithinthecachesysteminunitsknowascachelines.Cachelinesareapowerof2ofcontiguousUpcomingEventsbyteswhicharetypically32-2

2、56insize.Themostcommoncachelinesizeis64bytes.FalsesharingisatermwhichapplieswhenthreadsunwittinglyimpacttheperformanceofeachotherwhilemodifyingindependentvariablessharingthePerformanceTestingJavasamecacheline.WritecontentiononcachelinesisthesinglemostlimitingfactoronachievingscalabilityforparallelAp

3、plications-SkillsMatterLondonthreadsofexecutioninanSMPsystem.I’veheardfalsesharingdescribedasthesilentperformancekillerbecauseitisJavavs.C++PanelDebate-farfromobviouswhenlookingatcode.GOTOChicagoTop10PerformanceFolklore-Toachievelinearscalabilitywithnumberofthreads,wemustensurenotwothreadswritetothe

4、samevariableorcacheGOTOChicagoline.Twothreadswritingtothesamevariablecanbetrackeddownatacodelevel.Tobeabletoknowifindependentvariablessharethesamecachelineweneedtoknowthememorylayout,orwecangetatooltotellus.IntelVTuneissuchaprofilingtool.InthisarticleI’llexplainhowmemoryislaidoutforJavaobjectsandhow

5、wecanpadoutourAboutMecachelinestoavoidfalsesharing.MartinThompsonTechnologygeekexploringthecapabilitiesofmodernhardware.Availablefordevelopment,training,performancetuning,andconsultingservices.ViewmycompleteprofilePopularPostsCPUCacheFlushingFallacyEvenfromhighlyexperiencedtechnologistsIoftenheartal

6、kabouthowcertainoperationscauseaCPUcacheto"flush".Thissee...MemoryAccessPatternsAreImportantInhigh-performancecomputingitisoftensaidthatthecostofacache-missisthelargestperformancepenaltyforanalgorithm.Formany...NativeC/C++LikePerformanceForJavaObjectSerialisationDoyoueverwishyoucouldturnaJavaobjecti

7、ntoastreamofbytesasfastasitcanbedoneinanativelanguagelikeC++?Ifyouuses...CompactOff-HeapStructures/TuplesInJavaInmylastpostIdetailedtheimplicationsoftheaccesspatternsyourcodetakestomainmemory.Sincethe