Linux Kernel Structure and Principles: Work Queue [Author's Direct Lecture Part 1-7]

If you're a system software developer in fields such as system semiconductors and automotive

Essential Linux Kernel Knowledge

What is the most widely used operating system in all IT devices? It's the Linux operating system. It is used in smartphones, digital TVs, aviation entertainment systems, and servers. System semiconductor companies use Linux (Linux device drivers) to control the hardware they design. Additionally, Linux is extensively utilized in various components of electric vehicles (Automotive) such as infotainment, autonomous driving, and telematics.

The core of the Linux operating system is the Linux kernel. Along with the Armv8-A architecture, the Linux kernel can be considered the content that requires the most essential foundational knowledge currently needed in the system software industry.

However, the Linux kernel is like a massive barrier for beginners in the field of system software. Beginners have likely experienced giving up on learning the Linux kernel multiple times. That difficult Linux kernel is becoming increasingly complex as it evolves through version upgrades.After 2024, the Linux kernel version will be upgraded to v6.6 or higherHowever, the barriers to entry are becoming higher.

Linux system software developers positioned in various fields including system semiconductors and electric vehicles know that they need to understand the Linux kernel well to enhance their development capabilities. However, it's difficult to get a sense of how to learn the Linux kernel and, more importantly, what content they need to know well in practical work.

The Core of the Core in Linux Device Driver Development: Work Queues

When entering as a Linux system software developer, most people develop Linux device drivers. In this process,Essential features you must know about are work queuesHere are a few reasons:

• Work queues are used as a bottom-half interrupt handling technique.

• Many functions of device drivers are implemented using APIs provided by workqueues.

Additionally, many functions that make up the Linux kernel also operate using APIs provided by workqueues. Therefore, in Chapter 7 of my book "Structure and Principles of the Linux Kernel," I explain 'workqueues' as follows.

This lecture is structured to allow readers to learn about workqueues through various debugging practices (TRACE32 memory dump analysis, ftrace analysis).

Differentiation Points of the Course

This lecture consists of content that has never been covered on YouTube or any lecture platform before! We debug data structures related to Linux kernel workqueues (system_wq global variable, worker_pool structure, work_struct structure) through Linux kernel memory dumps. Those taking this lecture can download 3 memory dumps and practice hands-on.

You'll learn this content

We first explain the core features and roadmap that make up the work queue. Then we provide a detailed explanation of how to learn work queues effectively.

This explains the data structures that make up the workqueue from a big picture perspective. It provides detailed explanations of the structure of the global workqueue, worker pool, and work items.

Explains how work (work items) are used from a device driver perspective.

This introduces data structures related to work and provides detailed explanations of what values each field stores through debugging practice, making it easy to understand.

This provides a detailed explanation of the work item queuing process through kernel code analysis.

This provides a detailed explanation of the data structure (linked list) when work items are queued using TRACE32 memory dump debugging.

This introduces worker threads that execute work items and explains the execution stages of worker threads. It then analyzes the kernel source code where worker threads are created and also explains the call stack (back trace) of this process.

The operational behavior when worker threads execute is explained in detail through kernel source analysis.

Explains how work items are executed through worker threads using TRACE32 debugging. (3 memory dumps)

This provides a detailed explanation of ftrace for tracing workqueues and analyzes related kernel source code along with ftrace messages. ## ftrace Overview for Workqueue Tracing ftrace is a powerful kernel tracing framework in Linux that allows developers to trace various kernel subsystems, including workqueues. Workqueues are kernel mechanisms for deferring work to be executed later in process context. ## Key ftrace Events for Workqueue Tracing ### 1. workqueue_queue_work This event is triggered when work is queued to a workqueue. **Kernel Source Analysis:** ```c // kernel/workqueue.c static void __queue_work(int cpu, struct workqueue_struct *wq, struct work_struct *work) { struct pool_workqueue *pwq; struct worker_pool *pool; // ... code for selecting appropriate pool ... trace_workqueue_queue_work(req_cpu, pwq, work); // ... actual queuing logic ... } ``` **ftrace Message Example:** ``` kworker/0:1-123 [000] .... 123.456789: workqueue_queue_work: work struct=0xffff888012345678 function=flush_to_ldisc workqueue=

This provides an easy-to-understand explanation of delayed work queues, which are frequently used in device drivers.

We will analyze the source code of delayed work and the execution flow of delayed work in detail.

This explains the workqueue watchdog, which is not covered in the book but is frequently used in real-world projects. It describes how to enable CONFIG_WQ_WATCHDOG and analyzes the related kernel source code.

This provides a detailed explanation of the workqueue watchdog's operation through ftrace message analysis.

Based on book writing/teaching experience
Deeper and more detailed than anyone else!

Global Author & Linux System Software Developer (Arm, RISC-V Architecture)

In the field of domestic system software, this is an unprecedented! author who wrote books on 'Arm Architecture (Armv8-A, Armv7-A)' and 'Linux Kernel' (both books were selected as excellent books by the Korean Academy), and is a global author who was the first in Korea to write the book "Reverse Engineering Armv8-A Systems" (in English) through an overseas publisher (Packt). Above all, they are a working developer who best understands the latest system software trends (electric vehicles, system semiconductors - system software). They are also an educator who is most actively engaged in knowledge dissemination activities in the system software field.

• 'Reverse Engineering Armv8-A Systems: A practical guide to Kernel, Firmware, and TrustZone analysis' book (English) author, (Packt Publishing)

• 'Learning the Structure and Principles of the Linux Kernel through Debugging' (2021 Korea Academy of Sciences Excellence in Books Award) Author

• Author of 'Structure and Principles of Arm Architecture for System Software Development' (2024 Korea Academy Outstanding Book Award)

• 'Programmers Dev Course: Linux System and Kernel Expert' Main Instructor (1st-2nd cohorts)

• June 2022, Korea Computer Congress (KCC2022) - Tutorial Presentation [Conquering the Linux Kernel Using ftrace]

• LG Electronics 'Linux Kernel' and 'Armv8 Architecture' In-house Instructor (including domestic and overseas developers) - (2020~2024)

I can confidently say that I am an educator who can explain the major functions that make up the Linux kernel better than anyone else in Korea.

Pre-enrollment Reference Information