Fair And Efficient CPU Scheduling Algorithms Jeyaprakash Chelladurai BTech, University of Madras, Chennai, Tamil Nadu (India), 2003 Thesis Submitted In Partial Fulfillment of The Requirements For The Degree of Master of Science in Mathematical, Computer, And Physical Sciences (Computer Science) The University of Northern British Columbia December 2006 ©Jeyaprakash Chelladurai, 2006 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 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A bstract Scheduling in computing systems is an important problem due to its perva­ sive use in computer assisted applications. Among the scheduling algorithms proposed in the literature, round robin (RR) in general purpose computing and rate monotonic (RM) in real-time and embedded systems, are widely used and extensively analyzed. However, these two algorithms have some performance limitations. The main objective of this thesis is to address these limitations by proposing suitable modifications. These modifications yield many efficient versions of RR and RM. The appeal of our improved algorithms is that they alleviate the observed limitations significantly while retaining the simplicity of the original algorithms. In general purpose computing context, we present a generic framework called fair-share round robin (FSRR) from which many scheduling algorithms with different fairness characteristics can be derived. In real-time context, we present two generic frameworks, called off-line activation-adjusted scheduling (OAA) and adaptive activation-adjusted scheduling (AAA), from which many static priority scheduling algorithms can be derived. These algorithms reduce unnecessary preemptions and hence increase: (i) processor utilization in real­ time systems; and (ii) task schedulability. Subsequently, we adopt and tune AAA framework in order to reduce energy consumption in embedded systems. We also conducted a simulation study for selected set of algorithms derived from the frameworks and the results indicate that these algorithms exhibits improved performance. ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Contents A b stra c t .................................................................................................................... iii C ontents.................................................................................................................... iii List of Figures........................................................................................................... vii List of Tables ........................................................................................................... viii Publications.............................................................................................................. ix Acknowledgments .................................................................................................... x 1 Introduction 1 1.1 Motivation....................................................................................................... 3 1.2 Contribution.................................................................................................... 6 1.3 Thesis Organization....................................................................................... 8 2 C PU Scheduling 9 2.1 Scheduling in General Purpose Computing System s............................. 9 2.2 Scheduling in Real-Time System s ............................................................. 11 2.2.1 Scheduling in Hard Real-Time S ystem s ....................................... 13 2.3 Scheduling in Embedded Systems ............................................................. 17 2.4 Summary ....................................................................................................... 19 3 Simulator for Scheduling Algorithms 20 3.1 Sim ulation....................................................................................................... 20 3.2 Simulation System for Scheduling............................................................. 23 3.2.1 Performance M e tric s....................................................................... 24 iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2.2 Generation of Processes .................................................................. 25 3.2.3 Events in General Purpose Computing S ystem........................... 25 3.2.4 Generation of Tasks........................................................................... 25 3.2.5 Events in Real-Time and Embedded Systems .............................. 26 3.3 S u m m a ry ....................................................................................................... 27 4 Fair-Share Round Robin CPU Scheduling Algorithms 28 4.1 System Model and Problem Statem ent ................................................... 28 4.2 Round Robin Scheduling ............................................................................. 29 4.3 Fair-Share Round Robin Scheduling (FSRR) ......................................... 31 4.3.1 Informal D escrip tio n........................................................................ 31 4.3.2 Framework ........................................................................................ 33 4.3.3 RR vs. F S R R ..................................................................................... 35 4.3.4 FSRR Algorithms............................................................................... 36 4.4 Simulation S tu d y .......................................................................................... 38 4.4.1 Experimental S etu p ........................................................................... 38 4.4.2 Experiment and Result A nalysis ..................................................... 39 4.5 Related S chedulers ...................................................................................... 45 4.6 Summary ....................................................................................................... 47 5 Activation Adjusted Scheduling Algorithms for Hard Real-Time Sys­ tem s 48 5.1 System Model and Problem Statem ent ................................................... 48 5.2 Static Priority Scheduling Algorithms...................................................... 50 5.3 Off-line Activation-Adjusted Scheduling A lgorithm s ............................ 51 5.3.1 Framework ........................................................................................ 52 5.3.2 Computing R4 ..................................................................................... 54 5.3.3 OAA Scheduling A lgorithm s ........................................................... 54 5.3.4 OAA-RM Scheduling Algorithms .................................................. 55 5.3.5 A n aly sis ............................................................................................... 55 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.4 Adaptive Activation Adjusted Scheduling Algorithms ......................... 57 5.4.1 Framework ....................................................................................... 57 5.4.2 AAA Scheduling Algorithms .......................................................... 59 5.4.3 AAA-RM Scheduling A lg o rith m s................................................. 60 5.4.4 A n alysis .............................................................................................