Scheduling and locking in multiprocessor real-time operating systems

615 Pages·2011·3.395 MB·English

by  Björn B. Brandenburg

SCHEDULING AND LOCKING IN
MULTIPROCESSOR REAL-TIME OPERATING SYSTEMS
Bjo¨rnB.Brandenburg
A dissertation submitted to the faculty of the University of North Carolina at Chapel Hill
in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the
DepartmentofComputerScience.
ChapelHill
2011
Approvedby:
JamesH.Anderson
SanjoyK.Baruah
HermannHa¨rtig
JanF.Prins
F.DonelsonSmith
PaulE.McKenney
UMI Number: 3502550
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ABSTRACT
BJO¨RNB.BRANDENBURG:SchedulingandLockinginMultiprocessorReal-TimeOperating
Systems
(UnderthedirectionofJamesH.Anderson)
Withthewidespreadadoptionofmulticorearchitectures,multiprocessorsarenowastandard
deployment platform for (soft) real-time applications. This dissertation addresses two questions
fundamentaltothedesignofmulticore-readyreal-timeoperatingsystems: (1)Whichscheduling
policies offer the greatest flexibility in satisfying temporal constraints; and (2) which locking
algorithmsshouldbeusedtoavoidunpredictabledelays?
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WithregardtoQuestion1,LITMUS ,areal-timeextensionoftheLinuxkernel,ispresented
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and its design is discussed in detail. Notably, LITMUS implements link-based scheduling, a
novelapproachtocontrollingblockingduetonon-preemptivesections. Eachimplementedscheduler
(22configurationsintotal)isevaluatedunderconsiderationofoverheadsona24-coreIntelXeon
platform. Theexperimentsshowthatpartitionedearliest-deadlinefirst(EDF)schedulingisgenerally
preferableinahardreal-timesetting,whereasglobalandclusteredEDFschedulingareeffectiveina
softreal-timesetting.
WithregardtoQuestion2,real-timelockingprotocolsarerequiredtoensurethatthemaximum
delay due to priority inversion can be bounded a priori. Several spinlock- and semaphore-based
multiprocessorreal-timelockingprotocolsformutualexclusion(mutex),reader-writer(RW)exclu-
sion,andk-exclusionareproposedandanalyzed. AnewcategoryofRWlockssuitedtoworst-case
analysis,termedphase-fairlocks,isproposedandthreeefficientphase-fairspinlockimplementations
are provided (one with few atomic operations, one with low space requirements, and one with
constantRMRcomplexity).
Maximumpriority-inversionblockingisproposedasanaturalcomplexitymeasureforsemaphore
protocols. It is shown that there are two classes of schedulability analysis, namely suspension-
obliviousandsuspension-awareanalysis,thatyieldtwodifferentlowerboundsonblocking. Five
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asymptoticallyoptimallockingprotocolsaredesignedandanalyzed: afamilyofmutex,RW,and
k-exclusion protocols for global, partitioned, and clustered scheduling that are asymptotically
optimal in the suspension-oblivious case, and a mutex protocol for partitioned scheduling that is
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asymptoticallyoptimalinthesuspension-awarecase. ALITMUS -basedempiricalevaluationis
presentedthatshowstheseprotocolstobepractical.
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Tomyparents,HaraldandPetra.
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ACKNOWLEDGEMENTS
Iamindebtedtomanypeoplewhofirsthelpedmetogetintograduateschool,andthenhelped
metogetoutagain. Firstofall,Iwouldliketothankmyadvisor,JimAnderson,forhisunwavering
support, and my committee, Sanjoy Baruah, Hermann Ha¨rtig, Jan Prins, Don Smith, and Paul
McKenney,fortheirguidanceandadvice. Iwouldalsoliketoexpressmythanksandappreciationto
allmyco-authors,AaronBlock,HennadiyLeontyev,JohnCalandrino,UmaDevi,MacMollison,
ChrisKenna,AndreaBastoni,JonathanHermann,andAlexMills,andthestudentsinthereal-time
systems group that I sadly did not have a chance to write a paper with, Cong Liu, Glenn Elliott,
GuruprasadAphale,JeremyErickson,HaohanLi,BipasaChattopadhyay,andChih-HaoSun,for
theirhelpandfeedback. ManythanksalsotothefriendlyCSdepartmentstaff,andinparticularJodie
Turnbull,JohnSopko,MurrayAnderegg,andMikeStone,whohelpedmeinmanylargeandsmall
waysovertheyears.
IamgratefultotheGerman-AmericanFulbrightProgramandtheGraduateSchool’sDisserta-
tionCompletionFellowshipforfinancialsupportduringmyfirstandlastyearingraduateschool,
respectively. WithoutFulbright’ssupport,IprobablywouldnothaveattendedanAmericangraduate
school. SpecialthanksarealsoduetoJanPrins, forquicklyun-rejectingmyapplicationtoUNC
afteritendeduponthewrongpileduetoa“processingmishap.”
LifeinSittersonHallandBrooksBuildingwouldnothavebeenmuchfunwithoutmyfriendsin
theCSdepartment: AaronBlock,SasaJunuzovic,JayAikat,SeanCurtis,StephenOlivier,Keith
Lee,JamieSnape,SrinivasKrishnan,AnishChandak,JeffTerrell,StephenGuy—thanky’allfora
greattimeinNorthCarolina!
Outsideschool,IamgreatlyindebtedtoJasperMcChesney. Iwasveryluckytomeetyouby
chanceintheroommatelotteryandhavegreatlyenjoyedyourcompany—thankyouverymuchfor
themanyinterestingdiscussions,hikingtrips,andwonderfultimesofadvancednerdery. Inasimilar
vein,IwouldalsoliketothankDotHallforhercompassion,energy,andtheoccasionalcrazyidea.
ToobadthatweoverlappedinChapelHillforonlyashorttime.
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Very special thanks to Aaron and Nicki Block for their unrelenting support and mentorship.
Whenever I needed help or guidance, I knew I could count on you. You taught me a lot about
American culture; without you my stay in the U.S. would have been only half as interesting and
fun. Thankyouverymuchforyourgenerosityandfriendship. Onedaywewillfinishthatbikeride
aroundBerlin!
AnothercolleagueandfriendthatdeservesspecialmentionisAndreaBastoni,whowasavisiting
scholarwithUNC’sreal-timegroupfromOctober2009untilOctober2010. Thanksalotforallthe
funwehadinsideandoutsideofthedepartment,forthepaperswewrote,andforyourcontributions
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toLITMUS . Youcameatexactlytherighttime;unfortunatelyyouhadtoleaveagainafteronlya
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year. ThanksforstayinginvolvedwithLITMUS anyway.
Foremost, I thank my parents Harald and Petra for their unwavering support, understanding,
andencouragement,bothduringgraduateschoolandtheyearsbefore. Adefiningeventinmylife
wasthehighschoolexchangethatbroughtmetoMayfieldHighSchoolinLasCruces,NMduring
junioryear. InLasCruces,Idevelopedambitionandtenacity,withoutwhichthisdissertationwould
nothavebeenpossible. ForthisIwouldliketothankmyformerhostparentsBarbaraandGeorge
Stafford,whooutofthekindnessoftheirheartsopenedtheirdoortoanunknownteenager.
Finally,IamdeeplythankfultoNora,foralltheloveandsupport,forherpatience,forfollowing
mehalfwayaroundtheworldtoNorthCarolina,andforhertrustthatthiswasindeedtherightway. I
couldnothavefinishedthiswithoutyou.
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TABLE OF CONTENTS
LISTOFTABLES ........................................................................ xvi
LISTOFFIGURES .......................................................................xvii
LISTOFABBREVIATIONS ..............................................................xxiii
1 INTRODUCTION..................................................................... 1
1.1 TheCostofOver-Provisioning.................................................... 2
1.2 TheDivergenceofTheoryandPractice............................................ 3
1.2.1 Background .............................................................. 3
1.2.2 MultiprocessorReal-TimeScheduling ..................................... 6
1.2.3 Real-TimeLocking....................................................... 9
1.3 ThesisStatement................................................................. 10
1.4 Contributions .................................................................... 11
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1.4.1 LITMUS .............................................................. 11
1.4.2 ComprehensiveOverheadAccounting ..................................... 12
1.4.3 Overhead-AwareEvaluationMethodology ................................. 13
1.4.4 CaseStudy: MultiprocessorReal-timeSchedulingon24Cores ............. 14
1.4.5 Spin-BasedLockingProtocols ............................................ 14
1.4.6 EfficientPhase-FairSpinlockImplementations............................. 16
1.4.7 ANotionofOptimalityforSuspension-BasedLockingProtocols ........... 17
1.4.8 OptimalSuspension-BasedMultiprocessorLockingProtocols .............. 18
1.4.9 CaseStudy: TheImpactofOverheadsonLockingProtocols................ 19
1.5 Organization..................................................................... 20
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2 BACKGROUNDANDPRIORWORK................................................. 21
2.1 HardwareFoundations............................................................ 21
2.1.1 MultiprocessorsandMulticorePlatforms .................................. 21
2.1.2 ProcessorCaches......................................................... 25
2.1.3 Interrupts ................................................................ 34
2.1.4 TimersandClocks........................................................ 37
2.2 Real-TimeTaskModelandConstraints............................................ 41
2.2.1 TemporalCorrectness..................................................... 45
2.2.2 AlternateSoftReal-TimeDefinitions ...................................... 47
2.2.3 SchedulabilityAnalysisConcepts ......................................... 52
2.3 Real-TimeScheduling............................................................ 56
2.3.1 UniprocessorReal-TimeScheduling....................................... 58
2.3.1.1 Fixed-PriorityScheduling....................................... 58
2.3.1.2 Job-LevelFixed-PriorityScheduling............................. 62
2.3.2 PartitionedMultiprocessorReal-TimeScheduling.......................... 64
2.3.3 GlobalMultiprocessorReal-TimeScheduling.............................. 70
2.3.3.1 GlobalFixed-PriorityScheduling................................ 71
2.3.3.2 GlobalJob-LevelFixed-PriorityScheduling...................... 73
2.3.3.3 GlobalJob-LevelDynamic-PriorityScheduling .................. 86
2.3.4 ClusteredMultiprocessorReal-TimeScheduling ........................... 99
2.4 Real-TimeLockingProtocols..................................................... 101
2.4.1 ResourceModel..........................................................103
2.4.2 PriorityInversionBlocking ............................................... 107
2.4.3 UniprocessorReal-TimeLockingProtocols................................109
2.4.4 MultiprocessorReal-TimeLockingProtocols ..............................119
2.4.4.1 SpinlockProtocols..............................................120
2.4.4.2 SemaphoreProtocols ...........................................124
2.4.5 FurtherResultsinReal-TimeLocking .....................................134
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