MS Word - NCSU COE People.doc

《MS Word - NCSU COE People.doc》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、InterconnectionnetworksWhenmorethanoneprocessorneedstoaccessamemorystructure,interconnectionnetworksareneededtoroutedata—•fromprocessorstomemories(concurrentaccesstoasharedmemorystructure),or•fromonePE(processor+memory)toanother(toprovideamessage-passingfacility).In

2、evitably,alargebandwidthisrequiredtomatchthecombinedbandwidthoftheprocessingelements.»Oneextremeisasharedbus.HowdoesthecostscaleasthenumberofprocessorsNincreases?Howdoesthebandwidthscale?»Forconcurrentaccesstosharedmemory,theidealstructureisacrossbarswitch,whichcans

3、imultaneouslyconnectanysetofprocessorstoanysetofdistinctmemorymodules.AllNprocessorscanaccessallMmemoryunitswithanN´Mcrossbarswitch.Sincethereareusuallyaboutasmanyprocessorsasmemories,asprocessorsareadded,thecomplexityofacrossbarswitchgrowsasN2.Howdoesthebandwidthsc

4、ale?ForreasonablylargevaluesofN,thecrossbarswitchmaybemoreexpensivethantheprocessorsandmemories.»Formessagepassing,themostgeneralisthecompleteinterconnectionnetwork—apathfromeachprocessortoeveryotherprocessor.Lecture23ArchitectureofParallelComputers13Unfortunately

5、,thisrequiresbidirectionallinks.CostgrowswiththesquareofN.MeasuresofinterconnectionperformanceSeveralmetricsarecommonlyusedtodescribetheperformanceofinterconnectionnetworks:•Connectivity,ordegree,thenumberofnodesthatareimmediateneighborsofanode(i.e.,thenumberofnodes

6、thatcanbereachedfromitinonehop).•Diameter,themaximumnumberofnodesthroughwhichamessagemustpassonitswayfromsourcetodestination.Diametermeasuresthemaximumdelayintransmittingamessagefromoneprocessortoanother.Whatisthediameterofacrossbar?•Averagedistance,wherethedistance

7、betweentwonodesisdefinedbythenumberofhopsintheshortestpathbetweenthosenodes.Averagedistanceisgivenbydavg = whereNisthenumberofnodes,Ndisthenumberofnodesatdistancedapart,andristhediameter.•Bisectionwidth,thelargestnumberofmessagesthatcanbesentsimultaneously(withoutha

8、vingtwoormoremessagesusethesamewiresorroutingprocessor),nomatterwhichN/2nodesaresendingtowhichotherN/2nodes.Itisalsothesmallestnumberofwir