Architecting a Workload-agnostic Heterogeneous Multi-core Processor

128 Pages·2012·2.08 MB·English

by  Salil Vijay Wadhavkar

ABSTRACT
WADHAVKAR, SALIL VIJAY. Architecting a Workload-agnostic Heterogeneous Multi-core
Processor. (UnderthedirectionofDr. EricRotenberg.)
Improvingsingle-threadperformancestillremainsanimportantchallenge. Heteroge-
neousmulti-coresofferthepotentialofimprovingsingle-threadperformancebyproviding
a number of core types that capture a wide range of application behaviors. Some prior
approachesofchoosingtheconstituentcoresinaheterogeneousmulti-corehavefocusedon
reducingpowerconsumptionbyemployingmonotoniccores. Otherapproachesthataimto
improveperformanceassumeaprioriknowledgeoftheworkload. Itisuncertainhowsuch
workload-specificapproacheswouldperformiftheworkloadchangesinthefuture.
Thisdissertationaddressesthequestionofchoosingthecoresinaheterogeneousmulti-
coreinaworkload-agnosticmanner. Theprocessofselectingtheconstituentcoresiscom-
pletelyindependentofanybenchmarksuite. Wepresentseveralapproachesofchoosing
cores,andshowthattheresultingmulti-coredelivershighperformanceforalargenumber
ofapplicationphases.
We classify applications in one of four categories of kernels: pointer-chasing, array
manipulation, arbitrary serial and arbitrary parallel. We systematically vary instruction-
level parameters and evaluate the highest performing heterogeneous multi-cores using
synthetically generated kernels. Since the resulting multi-core is workload-agnostic, its
performanceonrealapplicationphasesisalmostasgoodasacustomizedheterogeneous
multi-core. Moreover,wedemonstratepotentialpitfallsofcustomizationbyshowingthat
multi-cores tuned to a subset of the actual workload may perform poorly on the entire
workload.
Weusestatisticaltoolssuchasclassificationtreestounderstandtherelationshipsbe-
tweeninstruction-levelparametersandcoresuitability. Theclassificationtreesareusedasa
startingpointforapplicationsteeringmechanisms. Weshowthatanapplicationsteering
mechanismbasedonclassificationtreesperformsbetterthanrandomsteeringonaverage.
(cid:13)c Copyright2012bySalilVijayWadhavkar
AllRightsReserved
ArchitectingaWorkload-agnosticHeterogeneousMulti-coreProcessor
by
SalilVijayWadhavkar
AdissertationsubmittedtotheGraduateFacultyof
NorthCarolinaStateUniversity
inpartialfulfillmentofthe
requirementsfortheDegreeof
DoctorofPhilosophy
ComputerEngineering
Raleigh,NorthCarolina
2012
APPROVEDBY:
Dr. EricRotenberg Dr. JamesTuck
ChairofAdvisoryCommittee
Dr. HuiyangZhou Dr. SteffenHeber
DEDICATION
ToAai,Baba,andAdu
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BIOGRAPHY
Salil Wadhavkar is from Mumbai, India. Prior to joining the Ph.D. program at NCSU, he
receivedhisM.S.E.degreeinElectricalEngineeringfromTempleUniversityin2006, and
B.E.degreeinElectronicsEngineeringfromtheUniversityofMumbai,Indiain2003. His
professionalinterestsincludecomputerarchitecture,heterogeneousmulti-cores,workload
analysis,andtheimpactoftechnologyoneverydaylife. DuringhisPhDprogram,hehadthe
opportunitytointernatIntelCorp. toworkonheterogeneoussystems. Heisastudentmem-
beroftheIEEE,ACM-SIGARCHandPhiKappaPhi. Inhissparetime,heplaysbadminton,
learnstoplaytheguitar,andpursuesphotography.
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ACKNOWLEDGEMENTS
ThelastsixyearsasaPhDstudentatNCStatehavebeensomeofmymostmemorableyears.
Throughtimesofdifficulty,stress,andthegeneralmiseryofgradlife,manyindividualshave
beenasourceofstrength,courage,supportandlove,andhavemadethisjourneyimmensely
fulfilling. Theseparagraphsrepresentafeebleattempttoshowmygratitudetothemina
ratherclumsyformofexpression,thatis,language.
I would like to thank my parents for their unconditional love, encouragement, and
support through the years. My achievements are a result of their nurture and the values
they instilled in me. Their support and sacrifices will always motivate and inspire me to
wholeheartedlypursuemydreams.
Ihavebeenveryfortunatetoworkwithmyadvisor, Dr. EricRotenberg. Hisabilityto
thinkdeeplyandcritically,aswellasarticulatecomplexideaswithclarityhasalwaysinspired
me. Hispassionforcomputerarchitecturehasinculcatedinmeastrongworkethicofalways
doingmybest,nomatterhowtrivialthetask. Mostimportantly,hisencouragementand
patiencehavetaughtmethevalueofpersistenceanddiligenceinaccomplishingone’sgoal. I
amalsogratefultohimforprovidingmewithfinancialsupportovertheyears.
I want to thank my committee members Dr. James Tuck, Dr. Huiyang Zhou, and Dr.
SteffenHeberfortheirconstructivefeedbackandcomments. Theirsuggestionshavebeen
veryvaluableinimprovingmydissertation.
LindaFontes,ElaineHardinandSandyBronsonhavealwaysprovidedpromptandhelpful
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administrativesupport. Iwouldliketothankthemforquicklyandsmoothlyprocessingall
paperwork,especiallyclosetodeadlines.
ThisresearchwassupportedbyNSFgrantCCF-0811707andgiftsfromIntelandIBM.
Anyopinions,findings,andconclusionsorrecommendationsexpressedhereinarethoseof
theauthoranddonotnecessarilyreflecttheviewsoftheNationalScienceFoundation.
My fellow CESR dwellers have been an exciting and intellectually stimulating group
of people to work with. In addition to being wonderful colleagues, they have been good
friends.IwanttothankNiketChoudhary,SandeepNavada,MuawyaAl-Otoom,ElliottForbes,
HashemHashemi,RamiAl-Sheikh,BrandonDwiel,MarkDechene,JayneelGandhi,Hiran
Mayukh,TanmayShah,andRajeshwarVankaformanybrainstormingsessions,insightful
discussions,andwittybanter.
Outside of CESR, my friends have been a source of diversion during stressful times.
Weekendget-togethersandtheoccasionalpokernightswithJitendraKumar,PradeepSharma,
AdwaitBachuwar,PrabhakarTembhurne,ShrirajMisal,AmitNaik,andShreekanthPavani
aremostmemorable,andprovidedamuchneededbreakfromthemonotonyofgradlife.
ConversationsandvirtualhangoutswithmycollegebuddiesNinadPradhan,RahulSaxena,
Raghvendra Cowlagi, and Robert Chettiar reminded me of life outside and beyond grad
school.
And finally, my wife and best friend, Aditi, has been my biggest source of inspiration,
encouragementandunrelentingsupport. Itisdifficulttoexpressinthesewoefullylimited
wordshowmuchIhavecherishedherloveandsupport. Shehasbeenbymysidethrough
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thetoughestoftimes,providingthestrengthtosuccessfullyperseverethroughgradschool.
Withoutherpatienceandunflaggingfaithinmyabilities,thisdissertationwouldneverhave
materialized.
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TABLEOFCONTENTS
LISTOFTABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
LISTOFFIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Chapter1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Chapter2 RelatedWork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 SelectionofCores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 StatisticalSimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 ApplicationSteering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Chapter3 EvaluationMethodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1 DesignSpace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2 RealisticPruningoftheDesignSpace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3 FabSim: TheCycle-accurateFabScalarSimulator . . . . . . . . . . . . . . . . . . . . . 18
3.3.1 CanonicalInterfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3.2 ModelingofClockedStructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3.3 Modelingpipelinedepth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3.4 SimulatorOptimizationsandFeatures . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3.5 FabSim/RTLco-simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3.6 ValidationofFabSim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.4 Benchmarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Chapter4 HeterogeneousMulti-coreDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.1 G21-TheProposedWorkload-agnosticHeterogeneousMulti-core. . . . . . . . . 33
4.2 PerformanceAnalysisofG21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.3 OtherWorkload-agnosticDesignApproaches . . . . . . . . . . . . . . . . . . . . . . . . 39
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