超级计算更深奥思维

DeeperTheworldhasanewfastestcomputer,thankstovideoTheultimategamesSPEEDfanaticsthattheyare,computernerdsliketocheckthewebsiteofTop500,acollaborationbetweenGermanandAmericancomputerscientiststhatkeepstabsonwhichoftheworld'ssupercomputersisthefastest.Top500OnNovember12ththewebsitereleaseditslatestlist,andunveiledanewchampion.11月12日，该网站发布了最新榜单，揭开了新一任冠军的面纱。ThecomputerinquestioniscalledTitan,anditlivesatOakRidgeNationalLaboratory,inIttookfirstplacefromanotherAmericanmachine,IBM'sSequoia,whichishousedatLawrenceLivermoreNationalLaboratory,inCalifornia.它是击败了另一台美国的计算机-IBM的红杉而取得冠军的，红杉位于加利福尼亚州的劳伦ThesetwomachineshavehelpedreassertAmerica'sdominanceofalistthathad,inthepastfewyears,beenheadedbycomputersfromChinaandJapan.Top500榜单上获得优势地位，而在过去数年，中国和日本的计TitanisdifferentfromthepreviouschampioninseveralForonething,itisanopensystem,meaningthatscientificresearcherswithsufficientlythornyproblemswillbeabletobidfortimeonit,inmuchthesamewaythatastronomerscanbidfortimeontelescopes.Sequoia,bycontrast,spendsmostofitstimerunninghush-hushsimulationsofexplodingnuclearweapons,andisthereforerarelyavailableforpublicuse.Titanhasanunusualdesign,AllsupercomputersarecomposedofthousandsofprocessorchipsharnessedOften,thesearederivativesofthecentralprocessingunits,orCPUs,thatsitattheheartofmodern,desktopmachines.ButTitanderivesthemajorityofitsoomph—morethan90%—fromtechnologyoriginallydevelopedforthevideo-gameindustry.Halfofits37,376processorsareordinary37376Buttheotherhalfaregraphicsprocessingunits,orThesearespecialiseddevicesdesignedtocopewithmodernvideogames,whicharesomeofthemostdemandingapplicationsanyhomemachineiseverlikelytorun.GPUChina'sTianHe-1machine,apreviousTop500champion,wasbuiltinthesameway,asare60othermachinesintheTop500list.Top5001号也是采用同样的方式搭建的，Top50060ParallelBroadlyspeaking,aCPU—whichwillbeexpectedtoruneverythingfromspreadsheetstovoice-recognitionsoftwaretoencodedvideo—hastobeageneralist,competentateverysortofmathematicaltaskbutexcellingatnothing.CPU—解码视频—AGPU,bycontrast,isdesignedtoexcelatonethingonly:manipulatinghugenumbersofthetrianglesoutofwhichallmoderncomputergraphicsaremade.相比之下，GPUSeveralyearsagoresearchersatNvidiaandAMDrealisedthatmanyscientificproblemswhichdemandhugeamountsofcomputingpower—everythingfromclimatesimulationsandmodellingcombustioninanenginetoseismicanalysisfortheoil-and-gasindustry—couldbetranslatedintoaformthatwasdigestiblebytheirGPUs.Soonafter,supercomputerbuilderssuchasCraybegantotakeBorrowingfromthegamesindustryinthiswaybringsseveralbenefits.OnebigoneisefficTitanisanupgradeofOakRidge'sexistingJaguarUpgradingJaguarwithordinaryCPUswouldhavemeantbuildingacomputerthatsuckedaround30MWofelectricitywhenrunningflatout—enoughjuicetopowerasmalltown.CPU对美洲虎进行升级，则意味着升级后的计算机在全速运行时将会狂饮大30MW的电力，这么多电力供给一个小镇都绰绰有余。BecauseGPUsaresogoodattheirspecialisedtasks,Titancanachieveitsblisteringperformancewhilesippingamodest8.2MW.GPU8.2MW的电力，不算Itmakessensefinancially,too,saysSumitGupta,headofsupercomputingatGPUThechipsthatthefirmsellstosupercomputer-makersarealmostidenticaltothoseitsellstoGPUGPUAsDrGuptaobserves,Thehistoryofhigh-performancecomputingislitteredwiththebodiesoffirmsthattriedtobuildproductsjustforthesupercomputingmarket.Byitself,it'sjusttoosmallaItisnotallupsides,GPUMachineslikeTitanachievetheirspeedbybreakingaproblemintothousandsoftinypiecesandfarmingeachouttoasingleprocessor.Ahelpfulanalogy,perhaps,ispaintingahouse:onestrategymightbetohireasinglepainter,butitisprobablyquickertoemployseveralpeopleandgiveeacharoomtodo.Notallproblemsaresusceptibletobeingchoppedupinsuchaway,TherequirementtotranslateaproblemintothesortofmathematicsthataGPUcandigestaddsanotherbarrier.GPUDrGuptagivestheexampleofthemodelsusedtosimulatehowacarwillreactinacrashasoneproblemthathassofarresistedwhattheindustrycallsthemassivelyparallelapproach.Cleverprogrammerscansometimesfindawayaroundsuchissues:ray-tracing,ahigh-quality,mathematicallyintenseapproachtocomputergraphicsthataimstosimulateindividuallightrays,was,ironically,longthoughttobethekindofproblemthatamodernGPUwouldstrugglewith.GPUYetatagraphicsconferencein2008,agroupofresearchersfromNvidiaannouncedthattheyhad,nevertheless,foundawaytodoit.2008OakRidgeandNvidiaplantoworkwithscientistswantingtimeonTitantoseeiftheiralgorithmscanbetweakedinsimilarways,tomakethemdigestiblebythenewmachine.DrGuptaisEventherecalcitrantcar-crashsimulations,h