RCU concepts

• Using RCU to Protect Read-Mostly Arrays
  • Situation 1: Hash Tables
  • Situation 2: Static Arrays
  • Situation 3: Resizable Arrays
• Review Checklist for RCU Patches
• RCU and lockdep checking
• Lockdep-RCU Splat
• RCU and Unloadable Modules
  • Unloading Modules That Use call_rcu()
  • rcu_barrier()
  • Implementing rcu_barrier()
  • rcu_barrier() Summary
  • Answers to Quick Quizzes
• PROPER CARE AND FEEDING OF RETURN VALUES FROM rcu_dereference()
  • EXAMPLE OF AMPLIFIED RCU-USAGE BUG
  • EXAMPLE WHERE THE COMPILER KNOWS TOO MUCH
  • WHICH MEMBER OF THE rcu_dereference() FAMILY SHOULD YOU USE?
  • SPARSE CHECKING OF RCU-PROTECTED POINTERS
• What is RCU? – “Read, Copy, Update”
  • 1. RCU OVERVIEW
  • 2. WHAT IS RCU’S CORE API?
    • rcu_read_lock()
    • rcu_read_unlock()
    • synchronize_rcu()
    • rcu_assign_pointer()
    • rcu_dereference()
  • 3. WHAT ARE SOME EXAMPLE USES OF CORE RCU API?
  • 4. WHAT IF MY UPDATING THREAD CANNOT BLOCK?
  • 5. WHAT ARE SOME SIMPLE IMPLEMENTATIONS OF RCU?
    • 5A. “TOY” IMPLEMENTATION #1: LOCKING
    • 5B. “TOY” EXAMPLE #2: CLASSIC RCU
  • 6. ANALOGY WITH READER-WRITER LOCKING
  • 7. FULL LIST OF RCU APIs
  • 8. ANSWERS TO QUICK QUIZZES
• RCU Concepts
  • Frequently Asked Questions
• Using RCU hlist_nulls to protect list and objects
  • Using ‘nulls’
    • 1) Lookup algo
    • 2) Insert algo
    • 3) Remove algo
  • Avoiding extra smp_rmb()
    • 1) lookup algo
    • 2) Insert function
• Reference-count design for elements of lists/arrays protected by RCU
• RCU Torture Test Operation
  • CONFIG_RCU_TORTURE_TEST
  • Output
  • Usage on Specific Kernel Builds
  • Usage on Mainline Kernels
• Using RCU’s CPU Stall Detector
  • What Causes RCU CPU Stall Warnings?
  • Fine-Tuning the RCU CPU Stall Detector
    • CONFIG_RCU_CPU_STALL_TIMEOUT
    • RCU_STALL_DELAY_DELTA
    • RCU_STALL_RAT_DELAY
    • rcupdate.rcu_task_stall_timeout
  • Interpreting RCU’s CPU Stall-Detector “Splats”
  • Multiple Warnings From One Stall
  • Stall Warnings for Expedited Grace Periods
• Using RCU to Protect Read-Mostly Linked Lists
  • Example 1: Read-mostly list: Deferred Destruction
  • Example 2: Read-Side Action Taken Outside of Lock: No In-Place Updates
  • Example 3: Handling In-Place Updates
  • Example 4: Eliminating Stale Data
  • Example 5: Skipping Stale Objects
  • Summary
• Using RCU to Protect Dynamic NMI Handlers
• RCU on Uniprocessor Systems
  • Example 1: softirq Suicide
  • Example 2: Function-Call Fatality
  • Example 3: Death by Deadlock
  • Summary
• A Tour Through TREE_RCU’s Grace-Period Memory Ordering
  • Introduction
  • What Is Tree RCU’s Grace Period Memory Ordering Guarantee?
  • Tree RCU Grace Period Memory Ordering Building Blocks
    • Tree RCU Grace Period Memory Ordering Components
    • Putting It All Together
    • Legal Statement
• A Tour Through TREE_RCU’s Expedited Grace Periods
  • Introduction
  • Expedited Grace Period Design
  • RCU-preempt Expedited Grace Periods
    • RCU-sched Expedited Grace Periods
    • Expedited Grace Period and CPU Hotplug
    • Expedited Grace Period Refinements
• A Tour Through RCU’s Requirements
  • Introduction
  • Fundamental Requirements
    • Grace-Period Guarantee
    • Publish/Subscribe Guarantee
    • Memory-Barrier Guarantees
    • RCU Primitives Guaranteed to Execute Unconditionally
    • Guaranteed Read-to-Write Upgrade
  • Fundamental Non-Requirements
    • Readers Impose Minimal Ordering
    • Readers Do Not Exclude Updaters
    • Updaters Only Wait For Old Readers
    • Grace Periods Don’t Partition Read-Side Critical Sections
    • Read-Side Critical Sections Don’t Partition Grace Periods
  • Parallelism Facts of Life
  • Quality-of-Implementation Requirements
    • Specialization
    • Performance and Scalability
    • Forward Progress
    • Composability
    • Corner Cases
  • Software-Engineering Requirements
  • Linux Kernel Complications
    • Configuration
    • Firmware Interface
    • Early Boot
    • Interrupts and NMIs
    • Loadable Modules
    • Hotplug CPU
    • Scheduler and RCU
    • Tracing and RCU
    • Accesses to User Memory and RCU
    • Energy Efficiency
    • Scheduling-Clock Interrupts and RCU
    • Memory Efficiency
    • Performance, Scalability, Response Time, and Reliability
  • Other RCU Flavors
    • Bottom-Half Flavor (Historical)
    • Sched Flavor (Historical)
    • Sleepable RCU
    • Tasks RCU
  • Possible Future Changes
  • Summary
  • Acknowledgments
• A Tour Through TREE_RCU’s Data Structures [LWN.net]
  • Introduction
  • Data-Structure Relationships
    • The rcu_state Structure
    • The rcu_node Structure
    • The rcu_segcblist Structure
    • The rcu_data Structure
    • The rcu_head Structure
    • RCU-Specific Fields in the task_struct Structure
    • Accessor Functions
    • Summary
    • Acknowledgments
    • Legal Statement