Reading A Task 2 Text Task 3 Task 1 Task 4 Task 6 Task 7 Task 8 Task 5 Task 9 Reading A.
RTAS new task model Chwa2018.rtas.org/wp-content/uploads/2018/05/S9.3.pdf · For each control task...
Transcript of RTAS new task model Chwa2018.rtas.org/wp-content/uploads/2018/05/S9.3.pdf · For each control task...
Jinkyu LeeSungkyunkwan University(SKKU)
ClosingtheGapbetweenStabilityandSchedulability:ANewTaskModelforCyber-Physicalsystems
Hoon SungChwa andKangG.ShinUniversityofMichigan
▪ Operationofphysicalsubsystem inaCPSismonitored&controlledbycyber/computational subsystem.▫ Examples:autonomousvehicles,medicaldevices,smartbuildings
Cyber-PhysicalSystems
Cyber-PhysicalSystemsFeedbackcontrolloop
Physical plant
Controllerreference
SensorActuatorstate
outputinput
Periodictaskmodel(T,C,D):Period,Worst-caseexecutiontime,Deadline
State-spacerepresentation
Real-timescheduling
Stability
Schedulability
PhysicalpartCyberpart Gap
• Stability• Mostphysicalsubsystemsaredesignedtotolerateoccasionalcontrolupdatemisses.• Trade-offbetween samplingrateand updatemisses
• Stability,controlperformance,resourceutilization
Motivation
Feedbackcontrolloop
Physical plant
Controller
SensorActuatorSampling
rate
Controlupdatemiss
▪ AdaptiveCruiseControl(ACC)▫ Goal:maintainasafedistance▫ Input:inter-vehicledistance(𝛿),velocity(∆𝑣)▫ Output:vehicleacceleration(𝑎)<speedcontrol>
▪ Periodic(feedback)controlloop▫ Samplingperiod:𝑇
CaseStudy:ADASsystem
▪ State-spacerepresentation
▪ Stabilityanalysis[Astrom andWittenmark 97]
CaseStudy:ADASsystem
𝑥 𝑘 + 1 = 𝐴𝑥 𝑘 + 𝐵𝑢(𝑘 − 𝑚 𝑘 )𝑢 𝑘 = −𝐾𝑥(𝑘)𝑥 𝑘 = 𝛿∆𝑣𝑎 T
𝑚 𝑘 : # of consecutive update misses at 𝑡5
Astrom andWittenmark.Computer-controlledsystems.Prentice-HallInc.,1997.
▪ Stabilityregion
Observation
▪ Stabilityregion
Observation
(100ms,3misses)
(40ms,10misses)
• Shorter samplingperiod->moretolerable consecutivecontrolupdatemisses
▪ Stabilityregion
Observation
• Shorter samplingperiod->moretolerable consecutivecontrolupdatemisses
• Shorterperiodallowingmoreupdatemisses->Stabilityguaranteewithmuchfewerresources
Whenm=0,171ms
Whenm=1,(1+1)140 = 280ms
Whenm=10,(10+1) 40 = 440ms
Effective control update period
(m:consecutivecontrolupdatemisses)
40ms
140ms
171ms
▪ Stabilityregion
Observation
▪ Controlperformance(standardquadraticperformanceindex)▫ Deviationfromthedesiredstate
▪ Controlperformancedegradesasboththesamplingperiodand#updatemissesincrease.
Observation
▪ Periodiccontroltaskbehaviorwithcontrolupdatemisses▫ Case1:controltaskwithperiodT,consecutivemisses2
▫ Case2:controltaskwithperiod3T,consecutivemisses0
Observation
▪ Therelationbetweensamplingperiod andupdatemissescanbeexploitedtoimprovebothcontrolperformance andresourceefficiency withoutlosingstability
▪ OurGoal
Implication
▪ Control-scheduleco-design▫ Optimalperiodassignmenttomaximizecontrolperformance▫ Onlineperiod-adjustmentschemes▫ Assumption:stricthardguaranteeofeverydeadline
▪ Fault-tolerantscheduling▫ Relaxationofstricthardreal-timeguarantees
▪ (m,k)-firmdeadline,skip-overmodel,weakly-hardtaskmodel▪ Allowoccasionalcontrolsignaldropsorskippingjobs
▫ Assumption:fixedorgiventaskperiods
StateoftheArt
Noconsiderationoninteractionbtw.taskperiod anddeadlinemisses
[Seto etal. 96][BiniandCervin 08][Xuetal. 15][Cervin etal. 04][Wuetal. 10][Aminifar etal. 12][Palopoli etal. 02][Khatib etal. 17]
[Cervin etal. 02][Martietal. 04][Castane etal. 06]
[Palopoli etal. 00][Branicky etal. 02][Kauer etal. 14][Goswami etal. 14][Soudbakhsh etal. 13][Majumdar etal. 11][Yoshimotoetal. 11]
OurApproach
NewCPStaskmodel
Newschedulingmechanism
• capturesthetrade-offbetweensamplingperiod andcontrolupdatemissesü Stability,controlperformance
• Determinestaskperiods andmanagedeadlinemissesü Improvescontrolperformancewithoutlosingstabilityü Utilizeslimitedresourcesefficiently
▪ Foreachcontroltask𝜏7
NewCPSTaskModel
(𝑇7, 𝐶7, 𝐷7)
Classicalreal-timetaskmodel
({(𝑚7, [𝑇7=7> 𝑚7 , 𝑇7=?@(𝑚7)])}, 𝐶7, 𝐷7)
NewCPStaskmodel
𝑚7:maximumtolerableconsecutivedeadlinemisses
Generalize
Stablepair
▪ Foragivensetofcontroltasks,▪ Step1[offlineparameterassignment]▫ Determine𝜏7: 𝑚7, 𝑇7, 𝐶7, 𝐷7 ({(𝑚7, [𝑇7=7> 𝑚7 , 𝑇7=?@(𝑚7)])}, 𝐶7, 𝐷7)
guaranteeingstability
▪ Step2[onlinestate-awarescheduling]▫ Generateactualschedulebydynamicallycontrollingdeadlinemisses(≤ 𝑚7)▫ Considerplantstatetomaximizecontrolperformancewithoutlosingstability
Problem
▪ Howtofindastable parameterassignment?
▪ Howtofindaperformance-optimal parameterassignmentamongstableparameterassignments?
OfflineParameterAssignment
▪ Howtofindastableparameterassignment?▫ Derivenecessaryconditions foratasksettobestable▪ Notionofcritical job
▫ Ajobissaidtobecritical,ifitisreleasedaftermissing𝑚7 consecutivejobdeadlines
▪ Ifallcriticaljobsareschedulable,thephysicalplantisstable
OfflineParameterAssignment
Time
𝐽7F 𝐽7G 𝐽7H 𝐽7I 𝐽7J 𝐽7K 𝐽7L 𝐽7M 𝐽7N
Criticaljob Jobrelease Deadlinemiss𝑇7
𝑚7 = 2
Stabilityofitsphysicalplant
Schedulabilityofacontroltask
▪ Howtofindastableparameterassignment?▫ Schedulability ofallcriticaljobs▪ Difficult todeterminetheschedulability▪ ∵ Criticaljobdynamicallychanges▪ ∵ Interferenceonacriticaljob varies
OfflineParameterAssignment
Time
𝐽7F 𝐽7G 𝐽7H 𝐽7I 𝐽7J 𝐽7K 𝐽7L 𝐽7M 𝐽7N
𝐽7F 𝐽7G 𝐽7H 𝐽7I 𝐽7J 𝐽7K 𝐽7L 𝐽7M 𝐽7N
miss miss miss miss
miss miss miss miss miss
Criticaljob
dependingonthescheduleofnon-criticaljobs
▪ Howtofindastableparameterassignment?▫ Assume astaticminimal jobschedule
▪ Onlycriticaljobsarescheduled
▫ Applyresponse-timeanalysis
OfflineParameterAssignment
Time
𝐽7F 𝐽7G 𝐽7H 𝐽7I 𝐽7J 𝐽7K 𝐽7L 𝐽7M 𝐽7N
𝑚7 + 1 ⋅ 𝑇7 = 3 ⋅ 𝑇7
Period
Deadline
𝑇7
▪ Howtofindaperformance-optimalparameterassignmentamongstableparameterassignments?▫ Optimizationproblem
▫ Exponentiallyincreasingsearchspace▪ Two-stepapproach
OfflineParameterAssignment
control performance index
stability region
schedulability of critical jobs
State-awareOnlineScheduling
▪ UponJOB-RELEASEorJOB-COMPLETION▫ Maintaintwotypesofqueue:readyqueueandwaitqueue▫ Checkthepossibilityofexecutingnon-criticaljobs
State-awareOnlineScheduling
▪ Howtoensuredeadlineguaranteesofallcriticaljobs?▫ Challenge
▪ Infinitenumber ofcriticaljobswillbereleasedinfuture▪ Synchronousreleaseisnolongerthecriticalinstant
▫ Ourapproach▪ Provethatsufficienttocheckonlyonecriticaljobthatwillbereleasedearliest▪ Developschedulability analysis
▪ Autonomousvehiclecontrolsystem▫ Adaptivecruisecontrol,lanekeepingcontrol,DC-servocontrol▫ 3controltasks+hardreal-timetasks
Evaluation
▪ Comparison
Evaluation
[Martietal. 04]
Ournewtaskmodel({(m,T)},C,D)
Traditionaltaskmodel(T,C,D)
Parameter assignment
Periodassignmentwithharddeadline
(m,T)assignment[Our-PA]
Online scheduling
State-awarescheduling
[Our-PA-SAS]
Critical-job-onlyscheduling[Our-PA]
Dynamic periodadjustmentunderEDF
[DPA-EDF]
Static periodassignmentunderRM[SPA-RM]
Martietal.Optimalstatefeedbackbasedresourceallocationforresource-constrainedcontroltasks.InRTSS,2004.
▪ Evaluationcriteria▫ Schedulingperformance(cyberpart)
▪ Thenumberoftasksetsschedulablebytheproposedtechnique
Evaluation
54%
39%Accommodatemorecontroltasks
withoutlosingstability
▪ Evaluationcriteria▫ Controlperformance(physicalpart)
▪ Cumulativeerrorfromdesiredstateforcontroltasks
Evaluation
32%
Summary
Static viewonstability
GAP
<Physicalpart> <Cyberpart>
Stability ofphysicalpart
Tolerable updatemisses Nodeadlinemissallowed
Identifykeyparameters andtheirrelationship
Propose anewtaskmodelthatcapturestherelationship
Improvebothcontrolperformance andresourceutilization
ReferenceSeto etal.Ontaskschedulability inreal-timecontrolsystems.InRTSS,1996.
BiniandCervin.Delay-awareperiodassignmentincontrolsystems.InRTSS,2008.
Xuetal.Exploitingjobresponse-timeinformationintheco-designofreal-timecontrolsystems.InRTCSA,2015.
Cervin etal.Thejittermarginanditsapplicationinthedesignofreal-timecontrolsystems.InRTCSA,2004.
Wuetal.Parameterselectionforreal-timecontrollersinresource-constrainedsystems.InIEEETransactionsonIndustrialInformatics, 2010.
Aminifar etal.Designinghigh-qualityembeddedcontrolsystemswithguaranteedstability.InRTSS,2012.
Palopoli etal.Synthesisofrobustcontrolsystemsunderresourceconstraints.InHSCC,2002.Khatib etal.Schedulingofembeddedcontrollersundertimingcontracts.InHSCC,2017.
Cervin etal.Feedback-feedforwardschedulingofcontroltasks.InReal-TimeSystems,2002.Martietal.Optimalstatefeedbackbasedresourceallocationforresource-constrainedcontroltasks.InRTSS,2004.
Castane etal.Resourcemanagementforcontroltasksbasedonthetransientdynamicsofclosed-loopsystems.InECRTS,2006.Palopoli etal.Real-timecontrolsystemanalysis:anintegratedapproach.InRTSS,2000.
Branicky etal.Schedulingandfeedbackco-designfornetworkedcontrolsystems.InCDC,2002.Kauer etal.Fault-tolerantcontrolsynthesisandverificationofdistributedembeddedsystems.InDATE,2014.
Goswami etal.Relaxingsignaldelayconstraintsindistributedembeddedcontrollers.InIEEETransactionsonControlSystemsTechnology,2014.Soudbakhsh etal.Co-designofcontrolandplatformwithdroppedsignals.InICCPS,2013.
Majumdar etal.Performance-awareschedulersynthesisforcontrolsystems.InEMSOFT,2011.
Yoshimotoetal.Optimalarbitrationofcontroltasksbyjobskippingincyber-physicalsystems.InICCPS,2011.
▪ Alinearsystemisasymptoticallystable ifalltrajectoriesconvergetotheorigin▫ Foranyinitialstate𝑥 𝑘S ,
Stability
𝑥 𝑘 → 0𝑎𝑠𝑘 → ∞
State-awareOnlineScheduling
▪ Whichnon-criticaljobtoexecute?▫ Considercurrentstateerrors
▪ Insteadystate,nobenefitbyexecutinganon-criticaljob▪ Intransientstate,controlperformanceimprovementbyquickreactiontoperturbation
▫ Chooseajobwiththelargesterrorfirst
Time
Transient SteadyOutpu
t
▪ Evaluationcriteria▫ Schedulingperformance(cyberpart)
▪ Thenumberoftasksetsschedulablewithoutlosingstability▫ Controlperformance(physicalpart)
▪ Thesumofperformancemeasuresforcontroltasks
▪ Tasksetgeneration▫ 3controltasks+hardreal-timetasks
Evaluation