Is Parallel Programming Hard, And, If So, What Can You Do About It?

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198 APPENDIX D. READ-COPY UPDATE IMPLEMENTATIONS5. Unbalanced tree.Looking further, CONFIG_HOTPLUG_CPU makessenseonlygivenCONFIG_SMP, andCONFIG_RCU_CPU_STALL_DETECTOR is independent, and really onlyneeds to be tested once (though someone even moreparanoid than am I might decide to test it both withand without CONFIG_SMP). Similarly, CONFIG_RCU_TRACE need only be tested once, but the truly paranoid(such as myself) wll choose to run it both withand without CONFIG_NO_HZ.ThisallowsustoobtainexcellentcoverageofRCUwith only 15 test cases. All test cases specify thefollowing configuration parameters in order to runrcutorture and so that CONFIG_HOTPLUG_CPU=n actuallytakes effect:CONFIG_RCU_TORTURE_TEST=mCONFIG_MODULE_UNLOAD=yCONFIG_SUSPEND=nCONFIG_HIBERNATION=nThe 15 test cases are as follows:1. Force single-node “tree” for small systems:CONFIG_NR_CPUS=8CONFIG_RCU_FANOUT=8CONFIG_RCU_FANOUT_EXACT=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y2. Force two-level tree for large systems:CONFIG_NR_CPUS=8CONFIG_RCU_FANOUT=4CONFIG_RCU_FANOUT_EXACT=nCONFIG_RCU_TRACE=nCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y3. Force three-level tree for huge systems:CONFIG_NR_CPUS=8CONFIG_RCU_FANOUT=2CONFIG_RCU_FANOUT_EXACT=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y4. Test autobalancing to a balanced tree:CONFIG_NR_CPUS=8CONFIG_RCU_FANOUT=6CONFIG_RCU_FANOUT_EXACT=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y5. Test unbalanced tree:CONFIG_NR_CPUS=8CONFIG_RCU_FANOUT=6CONFIG_RCU_FANOUT_EXACT=yCONFIG_RCU_CPU_STALL_DETECTOR=yCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y6. Disable CPU-stall detection:CONFIG_SMP=yCONFIG_NO_HZ=yCONFIG_RCU_CPU_STALL_DETECTOR=nCONFIG_HOTPLUG_CPU=yCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y7. Disable CPU-stall detection and dyntick idlemode:CONFIG_SMP=yCONFIG_NO_HZ=nCONFIG_RCU_CPU_STALL_DETECTOR=nCONFIG_HOTPLUG_CPU=yCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y8. Disable CPU-stall detection and CPU hotplug:CONFIG_SMP=yCONFIG_NO_HZ=yCONFIG_RCU_CPU_STALL_DETECTOR=nCONFIG_HOTPLUG_CPU=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y9. Disable CPU-stall detection, dyntick idle mode,and CPU hotplug:
D.2. HIERARCHICAL RCU OVERVIEW 199CONFIG_SMP=yCONFIG_NO_HZ=nCONFIG_RCU_CPU_STALL_DETECTOR=nCONFIG_HOTPLUG_CPU=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y10. Disable SMP, CPU-stall detection, dyntick idlemode, and CPU hotplug:CONFIG_SMP=nCONFIG_NO_HZ=nCONFIG_RCU_CPU_STALL_DETECTOR=nCONFIG_HOTPLUG_CPU=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=yThis combination located a number of compilerwarnings.11. Disable SMP and CPU hotplug:CONFIG_SMP=nCONFIG_NO_HZ=yCONFIG_RCU_CPU_STALL_DETECTOR=yCONFIG_HOTPLUG_CPU=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=y12. Test Classic RCU with dynticks idle but withoutpreemption:CONFIG_NO_HZ=yCONFIG_PREEMPT=nCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=yCONFIG_TREE_RCU=n13. Test Classic RCU with preemption but withoutdynticks idle:CONFIG_NO_HZ=nCONFIG_PREEMPT=yCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=nCONFIG_CLASSIC_RCU=yCONFIG_TREE_RCU=n14. Test Preemptable RCU with dynticks idle:CONFIG_NO_HZ=yCONFIG_PREEMPT=yCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=yCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=n15. Test Preemptable RCU without dynticks idle:CONFIG_NO_HZ=nCONFIG_PREEMPT=yCONFIG_RCU_TRACE=yCONFIG_PREEMPT_RCU=yCONFIG_CLASSIC_RCU=nCONFIG_TREE_RCU=nForalargechangethataffectsRCUcorecode, oneshould run rcutorture for each of the above combinations,and concurrently with CPU offlining andonlining for cases with CONFIG_HOTPLUG_CPU. Forsmall changes, it may suffice to run kernbench ineach case. Of course, if the change is confined to aparticular subset of the configuration parameters, itmay be possible to reduce the number of test cases.Torturing software: the Geneva Convention doesnot (yet) prohibit it, and I strongly recommend it!!!D.2.9 ConclusionThis hierarchical implementation of RCU reduceslock contention, avoids unnecessarily awakeningdyntick-idle sleeping CPUs, while helping to debugLinux’s hotplug-CPU code paths. This implementationis designed to handle single systems with thousandsof CPUs, and on 64-bit systems has an architecturallimitation of a quarter million CPUs, alimit I expect to be sufficient for at least the nextfew years.This RCU implementation of course has some limitations:1. The force_quiescent_state() can scan thefull set of CPUs with irqs disabled. This wouldbe fatal in a real-time implementation of RCU,so if hierarchy ever needs to be introduced topreemptable RCU, some other approach will berequired. <strong>It</strong> is possible that it will be problematicon 4,096-CPU systems, but actual testingon such systems is required to prove this oneway or the other.On busy systems, the force_quiescent_state() scan would not be expected to happen,as CPUs should pass through quiescent stateswithin three jiffies of the start of a quiescentstate. On semi-busy systems, only the CPUs in
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Is Parallel Programming Hard, And,
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Contents1 Introduction 11.1 Histori
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CONTENTSv6 Locking 676.1 Staying Al
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CONTENTSviiB Synchronization Primit
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CONTENTSixE.7.1 Introduction to Pre
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PrefaceThe purpose of this book is
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Chapter 1IntroductionParallel progr
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1.2. PARALLEL PROGRAMMING GOALS 3CP
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1.3. ALTERNATIVES TO PARALLEL PROGR
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1.4. WHAT MAKES PARALLEL PROGRAMMIN
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1.5. GUIDE TO THIS BOOK 9other hand
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Chapter 2Hardware and its HabitsMos
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2.1. OVERVIEW 13Therefore, as shown
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16 CHAPTER 2. HARDWARE AND ITS HABI
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18 CHAPTER 2. HARDWARE AND ITS HABI
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20 CHAPTER 3. TOOLS OF THE TRADE1 p
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22 CHAPTER 3. TOOLS OF THE TRADE1 p
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24 CHAPTER 3. TOOLS OF THE TRADE1.1
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26 CHAPTER 3. TOOLS OF THE TRADEQui
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28 CHAPTER 3. TOOLS OF THE TRADE
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30 CHAPTER 4. COUNTING1 atomic_t co
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32 CHAPTER 4. COUNTING4.2.3 Eventua
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34 CHAPTER 4. COUNTINGvanish when t
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36 CHAPTER 4. COUNTINGper-thread va
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38 CHAPTER 4. COUNTING1 unsigned lo
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42 CHAPTER 4. COUNTING1 #define THE
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46 CHAPTER 4. COUNTINGReadsAlgorith
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48 CHAPTER 5. PARTITIONING AND SYNC
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68 CHAPTER 6. LOCKING1 int delete(i
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70 CHAPTER 7. DATA OWNERSHIP
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72 CHAPTER 8. DEFERRED PROCESSINGfo
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74 CHAPTER 8. DEFERRED PROCESSINGth
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76 CHAPTER 8. DEFERRED PROCESSING
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82 CHAPTER 8. DEFERRED PROCESSINGNo
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108 CHAPTER 8. DEFERRED PROCESSING
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110 CHAPTER 9. APPLYING RCU1 struct
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112 CHAPTER 9. APPLYING RCU
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114 CHAPTER 10. VALIDATION: DEBUGGI
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116 CHAPTER 11. DATA STRUCTURES
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118 CHAPTER 12. ADVANCED SYNCHRONIZ
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138 CHAPTER 13. EASE OF USEFigure 1
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140 CHAPTER 13. EASE OF USE
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142 CHAPTER 14. TIME MANAGEMENT
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144 CHAPTER 15. CONFLICTING VISIONS
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146 CHAPTER 15. CONFLICTING VISIONS
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248 APPENDIX E. FORMAL VERIFICATION
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272 APPENDIX F. ANSWERS TO QUICK QU
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330 APPENDIX G. GLOSSARY(2) A physi
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332 APPENDIX G. GLOSSARYnear by. Th
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334 APPENDIX G. GLOSSARY
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336 BIBLIOGRAPHY[But97]USA, March 2
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338 BIBLIOGRAPHY[HMB06][Hol03][HP95
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340 BIBLIOGRAPHY[McK06] Paul E. McK
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342 BIBLIOGRAPHYtor. Software - Pra
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344 BIBLIOGRAPHY[UoC08][VGS08]Berke
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346 APPENDIX H. CREDITSH.4 Original
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