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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 TomyFamily...Amma,AnnaandMama 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. Iwouldlikethankmyfriend,GanaforallhispatienceandsupportduringthetimesIwas awayinthelabfordaystogether. ManythankstoNitinforallthetimehespentpatiently discussingvariousaspectsofmyworkinitsdevelopmentalstage. 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, Manish and Akshay for their sustained interest in my work and endless proddingto help me complete my thesis. My very special thanks to Roshan, who literally helped me turn thisthesisovertotheinstitute. WithouthissustainedhelpatthelastminuteIwouldhave beenlate. Finally, I would alsolike to extendmy gratituteto all my friends who have made my stayatWPI onetorememberforever. i 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 . . . . . . . . . 47 ii 3.3.4 Cache awaremeasurement-basedadmissioncontrol . . . . . . . . 48 3.4 DiskScheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.4.1 AlignmentofdiskservicethroughService Classes . . . . . . . . 56 3.4.2 ProtectionofServiceClasses . . . . . . . . . . . . . . . . . . . . 56 3.4.3 ProtectionofClientsWithinaServiceClass . . . . . . . . . . . . 57 3.4.4 AdaptabilitytoChangingSystemLoad . . . . . . . . . . . . . . 59 3.4.5 MinimizationofSeekandRotationalLatencies . . . . . . . . . . 60 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 iii 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 iv 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 v 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 vi

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in disk service timing. Current research Typically, disk scheduling mechanisms for multimedia applications reduce disk access times by only trying to Without his sustained help at the last minute I would have been late. Finally
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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 TomyFamily...Amma,AnnaandMama 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. Iwouldlikethankmyfriend,GanaforallhispatienceandsupportduringthetimesIwas awayinthelabfordaystogether. ManythankstoNitinforallthetimehespentpatiently discussingvariousaspectsofmyworkinitsdevelopmentalstage. 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, Manish and Akshay for their sustained interest in my work and endless proddingto help me complete my thesis. My very special thanks to Roshan, who literally helped me turn thisthesisovertotheinstitute. WithouthissustainedhelpatthelastminuteIwouldhave beenlate. Finally, I would alsolike to extendmy gratituteto all my friends who have made my stayatWPI onetorememberforever. i 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 . . . . . . . . . 47 ii 3.3.4 Cache awaremeasurement-basedadmissioncontrol . . . . . . . . 48 3.4 DiskScheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.4.1 AlignmentofdiskservicethroughService Classes . . . . . . . . 56 3.4.2 ProtectionofServiceClasses . . . . . . . . . . . . . . . . . . . . 56 3.4.3 ProtectionofClientsWithinaServiceClass . . . . . . . . . . . . 57 3.4.4 AdaptabilitytoChangingSystemLoad . . . . . . . . . . . . . . 59 3.4.5 MinimizationofSeekandRotationalLatencies . . . . . . . . . . 60 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 iii 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 iv 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 v 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 vi

Description:
in disk service timing. Current research Typically, disk scheduling mechanisms for multimedia applications reduce disk access times by only trying to Without his sustained help at the last minute I would have been late. Finally
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