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1、AnalyticalModelingofParallelSystemsAnanthGrama,AnshulGupta,GeorgeKarypis,andVipinKumarToaccompanythetext``IntroductiontoParallelComputing'',AddisonWesley,2003.TopicOverviewSourcesofOverheadinParallelProgramsPerformanceMetricsforParallelSystemsEffectofGra
2、nularityonPerformanceScalabilityofParallelSystemsMinimumExecutionTimeandMinimumCost-OptimalExecutionTimeAsymptoticAnalysisofParallelProgramsOtherScalabilityMetricsAnalyticalModeling-BasicsAsequentialalgorithmisevaluatedbyitsruntime(ingeneral,asymptoticru
3、ntimeasafunctionofinputsize).Theasymptoticruntimeofasequentialprogramisidenticalonanyserialplatform.Theparallelruntimeofaprogramdependsontheinputsize,thenumberofprocessors,andthecommunicationparametersofthemachine.Analgorithmmustthereforebeanalyzedinthec
4、ontextoftheunderlyingplatform.Aparallelsystemisacombinationofaparallelalgorithmandanunderlyingplatform.AnalyticalModeling-BasicsAnumberofperformancemeasuresareintuitive.Wallclocktime-thetimefromthestartofthefirstprocessortothestoppingtimeofthelastprocess
5、orinaparallelensemble.Buthowdoesthisscalewhenthenumberofprocessorsischangedoftheprogramisportedtoanothermachinealtogether?Howmuchfasteristheparallelversion?Thisbegstheobviousfollowupquestion-whatsthebaselineserialversionwithwhichwecompare?Canweuseasubopt
6、imalserialprogramtomakeourparallelprogramlookRawFLOPcount-WhatgoodareFLOPcountswhentheydontsolveaproblem?SourcesofOverheadinParallelProgramsIfIusetwoprocessors,shouldntmyprogramruntwiceasfast?No-anumberofoverheads,includingwastedcomputation,communication
7、,idling,andcontentioncausedegradationinperformance.Theexecutionprofileofahypotheticalparallelprogramexecutingoneightprocessingelements.Profileindicatestimesspentperformingcomputation(bothessentialandexcess),communication,andidling.SourcesofOverheadsinPar
8、allelProgramsInterprocessinteractions:Processorsworkingonanynon-trivialparallelproblemwillneedtotalktoeachother.Idling:Processesmayidlebecauseofloadimbalance,synchronization,orserialcomponents.ExcessComputation:Thisiscompu
