Better Admission Control and Disk Scheduling for Multimedia

149 Pages·2002·0.4 MB·English

Better Admission Control and Disk Scheduling for Multimedia
Applications
by
BadrinathVenkatachari
AThesis
SubmittedtotheFaculty
ofthe
WORCESTER POLYTECHNICINSTITUTE
Inpartialfulfillmentoftherequirementsforthe
DegreeofMasterofScience
in
ComputerScience
by
January2002
APPROVED:
Prof. MarkL.Claypool,ThesisAdvisor
Prof. RobertE.Kinicki,ThesisReader
Prof. MichaHofri,Head ofDepartment
Abstract
General purposeoperating systemshave been designedto providefast, loss-free disk
service to all applications. However, multimedia applications are capable of tolerating
somedataloss,butareverysensitivetovariationindiskservicetiming. Currentresearch
effortstohandlemultimediaapplicationsassumepessimisticdiskbehaviourwhendecid-
ing to admit new multimedia connections so as not to violate the real-time application
constraints. However, since multimedia applications are soft real-time applications that
cantoleratesomeloss,weproposeanoptimisticschemeforadmissioncontrolwhichuses
average case values for disk access taking advantage of caching in the operating system
and on the hard disk controller. We have also optimized the measurement based admis-
sion controller to admitvariable bandwidthmultimediaclients evenwhen the requesting
client’srequirementscannotbecompletelymet. Weassumethatthemultimediafileshave
beenencodedasmultiplelayers,eachaddingresolutiontothepreviousone.
Typically,diskschedulingmechanismsformultimediaapplicationsreducediskaccess
timesbyonlytryingtominimizemovementtosubsequentblocksafter sequencingbased
on Earliest Deadline First. We propose to implement a disk scheduling algorithm that
prioritizesrequeststohelpalignservicetoapplicationrequirements. Thediskscheduling
algorithm uses knowledge of the media stored (like MPEG or Realmedia) and permissi-
blelossand jitterfor each client,inadditiontothephysicalparametersusedbytheother
schedulingalgorithms,toschedulerequestsefficiently. We evaluateourapproach by im-
plementingour admission control policy and disk schedulingalgorithm inside the Linux
kernel under a framework called Clarity and measuring the quality of various mul-
timedia streams and performance of non-multimedia applications. Clarity provides
better bandwidth utilization by admitting more multimedia clients than the traditional
pessimistic approach. It also guarantees disk bandwidth availability to clients of a par-
ticular class in the presence of a large number of clients of other classes. This results in
fewer deadlines violations for multimedia clients, higher throughput and lower average
response time for non-multimediaclients. We find thatour approach results in improved
performance for multimedia and non-multimedia applications. The contributions of this
thesisare thedevelopmentof a new admissioncontroland flexibledisk schedulingalgo-
rithmforimprovedmultimediaqualityofserviceandtheirimplementationonLinux.
2
Acknowledgments
For me, it has been a big journey from the start to finish. A journey that has been
wrought with endless sleepless nights, disappointments, and a lot of struggle. Needless
tosay,thattheonlythingthatkeptmegoingwasthesupportofanumberofpeople. First
andforemost,Prof. MarkClaypool. Mark,“Withoutyourunstintingsupport,faithinmy
work, there is just no way that I could have completed my thesis. You have been always
there whenever I needed your help in any form and that is what saw me through times
of confusion, and helplessness. I guess no words can adequately describe what youhave
done for me and my work as an advisor, and companion. I thank you for everything.” I
thank my reader, Prof. Bob Kinicki for taking the time to read my thesis carefully and
givingnumeroussuggestionstoimproveit.
Thereareanumberoffriendswhohavecontributegreatlytotheclosureonmythesis.
Iwouldlikethankmyclosefriend,GanaforallhispatienceandsupportduringthetimesI
wasawayinthelabfordaystogether. Icannotthinkofanythingmorehecouldhavedone
tohelpmeconcentrateonmyresearch. Inthedevelopmentalstageofmywork,Ispenta
lot of time with Nitin discussing the various aspects of my work. While he would claim
tounderstandnothing,itusuallyendedupwithmyclarifying/rectufyingsomemethodor
assumption of mine. I thank him for all the time he spent patiently listening to my rant
(mostlyverylateinthenight/veryearlyinthemorning).
I thank Srikanth for his support and help with many things including numerous trips
tothelabtorebootthemachinewheneverIlostremoteconnectivity. Withoutthat,work-
ing seamlessly away from school would have been impossible. Many thanks to Pravin,
ManishandAkshayfortheirsustainedinterestandendlessproddingtohelpmecomplete
mythesis. MyveryspecialthankstoRoshan,wholiterallyhelpedmeturnthisthesisover
totheinstitute. WithouthissustainedhelpatthelastminuteIwouldhavebeenlate.
Finally, I would alsolike to extendmy gratituteto all my friends who have made my
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stayatWPI onetorememberforever.
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Contents
1 Introduction 1
1.1 Diskschedulingformultimedia. . . . . . . . . . . . . . . . . . . . . . . 8
2 Related Research 14
2.1 DiskScheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.1 MultimediaOperatingSystems . . . . . . . . . . . . . . . . . . 15
2.1.2 ModificationstoPresentOperatingSystems . . . . . . . . . . . . 16
2.1.3 SimulationDrivenDiskScheduling . . . . . . . . . . . . . . . . 18
2.2 AdmissionControl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1 MPEGLayeringofVideo . . . . . . . . . . . . . . . . . . . . . 24
2.2.2 Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.3 LinuxImplementations . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3 Clarity 28
3.1 ServiceClasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 LayeredMultimediaStreams . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3 AdmissionControl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3.1 OptimisticAdmissionControl . . . . . . . . . . . . . . . . . . . 37
3.3.2 Measurement-basedAdmissionControl . . . . . . . . . . . . . . 42
3.3.3 AdaptiveMeasurement-basedAdmissionControl . . . . . . . . . 46
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3.3.4 Cache awaremeasurement-basedadmissioncontrol . . . . . . . . 48
3.4 DiskScheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.4.1 AlignmentofdiskservicethroughService Classes . . . . . . . . 55
3.4.2 ProtectionofServiceClasses . . . . . . . . . . . . . . . . . . . . 56
3.4.3 ProtectionofClientsWithinaServiceClass . . . . . . . . . . . . 57
3.4.4 AdaptabilitytoChangingSystemLoad . . . . . . . . . . . . . . 59
3.4.5 MinimizationofSeekandRotationalLatencies . . . . . . . . . . 59
3.4.6 AwarenessofCachingPoliciesinLinux . . . . . . . . . . . . . . 60
3.4.7 AbilitytoExploitInherentMediaCharacteristics . . . . . . . . . 61
3.4.8 EfficiencyinComputation . . . . . . . . . . . . . . . . . . . . . 62
4 Implementation ofClarity 63
4.1 SystemConfiguration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2 AdmissionController . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.2.1 SystemCalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.3 DiskScheduler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.3.1 SystemCalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.3.2 ImplementationConsiderations . . . . . . . . . . . . . . . . . . 71
5 Performance Evaluationand Results 84
5.1 DeterminationofRunningTimeforClients . . . . . . . . . . . . . . . . 86
5.2 AdmissionControl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.3 Diskscheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6 Conclusion 126
7 Future Work 130
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List of Figures
3.1 ClarityintheLinuxkernel . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Flow-chartforadmissioncontrol . . . . . . . . . . . . . . . . . . . . . . 41
5.1 Determinationof Client ExecutionTime: Average response times versus
Clientexecutiontimesfor10clients . . . . . . . . . . . . . . . . . . . . 87
5.2 DeterminationofClientExecutionTime: AveragethroughputversusClient
executiontimesfor10clients . . . . . . . . . . . . . . . . . . . . . . . . 88
5.3 Number of clients admittedby pessimistic, optimisticand measurement-
basedadmissioncontrollersfora blocksizeof1KB . . . . . . . . . . . . 90
5.4 Number of clients admittedby pessimistic, optimisticand measurement-
basedadmissioncontrollersfora blocksizeof2KB . . . . . . . . . . . . 91
5.5 Number of clients admittedby pessimistic, optimisticand measurement-
basedadmissioncontrollersfora blocksizeof4KB . . . . . . . . . . . . 92
5.6 Measurement-based admission control: Disk bandwidth consumed for
variousdiskblocksizes . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.7 Comparison of measurement-based admission control and its adaptive
variation for various block sizes: Number of MPEG-like clients admit-
ted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.8 Fraction of total bandwidth consumed by MPEG-like clients under the
adaptivemeasurement-basedadmissioncontrolscheme . . . . . . . . . . 98
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5.9 PerformancecomparisonofLinuxandClarityinthepresenceofonly
non-multimediaclients: Averagethroughput . . . . . . . . . . . . . . . . 101
5.10 PerformancecomparisonofLinuxandClarityinthepresenceofonly
non-multimediaclients: Averageresponsetime . . . . . . . . . . . . . . 102
5.11 BandwidthpartitioningunderLinuxinthepresenceofexcessnon-multimedia
clients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.12 Percentage of deadlines missed under Linux and Clarity in the pres-
enceofexcessnon-multimediaclients . . . . . . . . . . . . . . . . . . . 105
5.13 Bandwidth partitioning under Clarity in the presence of excess non-
multimediaclients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.14 Jitter comparison for multimedia clients under Linux and Clarity in
thepresence ofexcessnon-multimediaclients . . . . . . . . . . . . . . . 108
5.15 BandwidthpartitioningunderLinuxinthepresenceofexcessmultimedia
clients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.16 BandwidthpartitioningunderClarityinthepresenceof excessmulti-
mediaclients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.17 Average throughput for non-multimediaclients under Linux and Clar-
ityinthepresenceofexcessmultimediaclients . . . . . . . . . . . . . 112
5.18 Averageresponsetimefornon-multimediaclientsunderLinuxandClar-
ityinthepresenceofexcessmultimediaclients . . . . . . . . . . . . . 114
5.19 Blocks serviced under Linux and Clarity in the presence of excess
multimediaclients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
5.20 Disk utilization with and without bandwidth re-allocation policies under
Claritywhenmultimediaserviceclassisunder-utilized . . . . . . . . 117
5.21 Average throughput with and without bandwidth re-allocation policies
underClaritywhenmultimediaserviceclassisunder-utilized . . . . . 118
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5.22 Averageresponsetimewithandwithoutbandwidthre-allocationpolicies
underClaritywhenmultimediaserviceclassisunder-utilized . . . . . 119
5.23 Jitter observed by multimedia clients with and without bandwidth re-
allocation policies under Clarity when multimedia service class is
under-utilized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.24 Disk utilization with and without bandwidth re-allocation policies under
Claritywhennon-multimediaserviceclassisunder-utilized . . . . . . 121
5.25 Average throughput with and without bandwidth re-allocation policies
underClaritywhennon-multimediaserviceclassisunder-utilized . . 123
5.26 Averageresponsetimewithandwithoutbandwidthre-allocationpolicies
underClaritywhennon-multimediaserviceclassisunder-utilized . . 124
5.27 Percentage of deadlines missed under Linux and Clarity in the pres-
enceofexcessnon-multimediaclients . . . . . . . . . . . . . . . . . . . 125
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