Red Hat Enterprise Linux Kernel Internals (RHD361)

Working with the Developer Community

• * Community Linux Kernel Development

• Why Contribute Kernel Code Upstream?

• Licensing

• Copyright

• Submitted Work

• The Kernel Development Process

• Creating Patches for the Merge Window

• Staging Trees

User Mode and Kernel Mode

• The Linux Kernel - An Overview

• The Role of the Kernel

• Kernel Contexts

• Four Milliseconds in the Life of the Kernel

• System Ring Levels

• Kernel Mode

• User Mode

• Mode Switching Example: System Calls

• x86 System Call Interface

• x86 System Call Interface (cont.)

• Mode Switching Example: IRQ Event

• Kernel Mode Linux

Kernel Compilation and Tools

• Kernel Packages

• Kernel Version

• Kernel Documentation

• Kernel Source Layout

• Kernel Source Layout (cont.)

• Recompiling the Red Hat Kernel

• Install Kernel Development Packages

• Kernel Source Package

• Preparing Source Code for Compilation

• Customizing Kernel Name (Optional)

• Choosing Compilation Options

• Compiling the Kernel and Modules

• Installing the Kernel Modules

• Installing the Compiled Kernel and Related Files

• Kernel Application Binary Interface (kABI)

• cscope

• LXR

• git

• git Documentation

Modules

• Kernel Modules

• Kernel Module Utilities

• Mapping Modules to Attached Devices

• Kernel Module Essentials

• modinfo Macros

• printk()

• /proc/kmsg and klogd

• printk() Loglevels

• Rate Limiting printk()

• Putting It All Together: A Simple Module

• Compiling a Module

• Integrating A New Module with the Kernel

• Makefile and Kconfig

• Module Parameters

• Example: Module with Parameter

Kernel API Overview

• Multitasking, Stacks, and Task-Descriptors

• Contents of a Program's Stack

• Kernel Mode Switch and the Stack

• Task Structures

• What Is a Process?

• thread_info Structure

• task_struct: Process Identifiers

• task_struct: Process State

• task_struct: Scheduling Information

• Doubly Linked Lists

• Doubly Linked Lists: Manipulation

• Doubly Linked Lists: Iteration

• Doubly Linked Lists: Processes

• task_struct: Related Processes

• task_struct: Statistics

• Allocating Kernel Memory: kmalloc()

• Memory Cache Optimizations: Branch Prediction

• Memory Cache Optimizations: Binding Structures

• Generating Kernel Errors

Synchronization

• Critical Sections

• Mutual Exclusion Devices

• Linux Mutex Toolbox

• Atomic Bit Operations

• Atomic Integers

• Spinlocks

• Spinlocks and Local Interrupts

• Read-Write Spinlocks

• Mutexes

• Semaphores

• Spinlock/Mutex Example

• Alternatives to Locking

• Sequential Locks

• Read-Copy-Update (RCU)

• Linux RCU Implementation

• Per-CPU Variables

• Completions

• The Big Kernel Lock

Kernel Debugging 1: Tools and Techniques

• Debugging Preparations

• kernel-debuginfo Warnings

• Kernel vs. User Space

• Live vs. Postmortem Debugging

• Crashes vs. Hangs

• Debugging Device Drivers

• User Space Debugging Tools

• /proc Kernel Information

• kernel.panic Tunable and Kernel Crashes

• /sys Filesystem

• debugfs Filesystem

• Printing from the Kernel

• Kernel Oops Messages

• SysRq Mechanism

• sosreport

• The crash Tool

• crash Requirements

• crash Installation

• crash Invocation

• crash Invocation Output

• crash Help

• crash Command Input

• crash Command Output

• crash Command Overview

• crash Default Context

Interrupts

• Interrupts

• Nature of Interrupts

• Types of Interrupts

• Interrupt Specific Hardware

• Interrupt Descriptor Table (IDT)

• IDT Initialization

• IDT Initialization Functions

• Exception Handling

• Asynchronous Interrupt Handling

• Interrupt Handler Considerations

• irq_desc Structure

• irqaction Structure

• Interrupt Handler Registration

• Performing Deferred Work

• Softirqs

• Using Softirqs

• Tasklets

• Using Tasklets

• Work Queues

• Work Queue Data Structures

• Using Work Queues

Device Driver Overview

• Device Drivers

• Device Types

• Device Nodes

• Creating a Device Node

• Dynamic Loading of Driver Modules

• Major and Minor Numbers

• Dynamic Major and Minor Numbers

• Dynamically Created Device Nodes

• Dynamically Created Device Nodes Made Easy

• Device Driver Essentials

• Character Device Registration

• Device Driver File Operations

• Driver Methods

• The file Structure

• The inode Structure

• The open and release Methods

• The read and write Methods

• Module Usage Count

• Simple Character Driver Example

Memory Management

• Virtual Memory and Paging

• x86 Memory Architecture

• Memory Segmentation in Linux

• x86 Segmentation

• x86 Segmentation in Linux

• Memory Paging

• Page Tables

• Mapping Virtual Addresses (x86)

• Mapping Virtual Addresses (x86-64)

• Memory Zones

• Arranging the Virtual Address Space

• ZONE_NORMAL

• ZONE_HIGHMEM

• ZONE_DMA

• Kernel Memory Allocation

• Memory Management

• Buddy Allocator

• Requesting and Releasing Page Frames

• Slab Allocator

• Slab Allocator (cont.)

• Non-Contiguous Memory Area Management

• Memory Flags: gfp_mask

• __get_free_pages()

• kmalloc()

• vmalloc()

Processes

• Creating Processes

• Sharing Resources

• do_fork()

• Process Memory Maps

• Memory Areas

• vm_flags

• pmap

• Kernel Threads

• Process 0

• Destroying Processes

• Context Switches

• When Does Context Switching Occur?

• When Is need_resched Set?

• When Is schedule() Called?

• Kernel Preemption

The Scheduler

• Priority

• Priority for Normal Processes

• Priority for Real-Time Processes

• Time Slices

• The O(1) Scheduler: Run Queues

• The O(1) Scheduler: Priority Arrays

• The O(1) Scheduler: How it works

• Wait Queues

• The O(1) Scheduler: Load Balancing

• The O(1) Scheduler: load_balance()

• Problems with the O(1) Scheduler

• O(1) Scheduler vs. CFS

• Overview of CFS

• Details of CFS

• CFS Task Scheduling

• CFS Scheduler Policies

• CFS Scheduler Classes

• CFS fair_sched_class

• CFS Tuning

• CFS Group Scheduling

• CONFIG_FAIR_GROUP_SCHED

• CONFIG_FAIR_CGROUP_SCHED

Kernel Timing

• The Need for Timing

• Timing Hardware

• Timing Source Selection

• Wall/Real Time: xtime

• Wall Clock System Calls

• Kernel Ticks: jiffies

• Software Timers

• POSIX Timers

• Interval Timers and alarm()

• High-Resolution Timers

• Timer Interrupt Handler

• TIMER_SOFTIRQ Softirq

• Delay Functions

SystemTap

• Introduction to SystemTap

• SystemTap's Main Components

• Monitoring the Kernel with SystemTap

• The stap Command

• Flow of Data in SystemTap

• Common Tapset Probe Points

• SystemTap Script Examples

System and Kernel Initialization

• Boot Sequence Overview

• BIOS Initialization

• Bootloader

• Starting the Boot Process: GRUB

• Bootloader Components

• The Chicken/Egg Module Problem and the Initial RAM Disk

• GRUB and grub.conf

• Kernel Initialization Overview

• __init and __initdata

• Initialization Subsections and Ordering

• Kernel Initialization

• init/main.c: start_kernel()

• init/main.c: rest_init()

• init/main.c: init()

• init/main.c: do_basic_setup()

• init/main.c: init_post()

• init Initialization

• Run Levels

Kernel Debugging 2: Crash Dumps

• Introduction to Crash Dumps

• Netdump/Diskdump Challenges

• Kdump

• Kdump Solution

• Kexec

• Relocatable Kernel

• In-place Kernel Decompression

• Starting Kdump

• Kdump Initrd Image

• Configuring Kdump

• Kdump Core Dumps to the Local System

• Kdump Core Dumps to NFS Mount Points

• Kdump Core Dumps to SSH Servers

• Dump File Size

• Customizing the Dump Capture Method: makedumpfile

• Dump Filtering

• Dump Compression

• Future Challenges

Unit 17 - Red Hat Enterprise Linux Realtime Kernel

• Realtime (RT) Linux

• Benefits of a Realtime Kernel

• Response Time Comparisons

• Wake-Up Response Time Example

• Changes in the Kernel

• Changes in the C Library

• RT Measurement Tools

• RT Tuning Tools

• RT Tuning Methods

• Loading the RT Kernel

NOTE: Course outline is subject to change with technology advances and as the nature of the underlying job evolves. For questions or confirmation on a specific objective or topic, please contact a Red Hat training specialist.