Understanding CPU Scheduling Fundamentals in Linux

This article delves into the core principles of CPU scheduling in Linux, starting with an overview of the physical CPU structure and the concept of per-CPU runqueues. It distinguishes between real-time scheduling, which prioritizes high-priority tasks through multi-priority queues, and the fair scheduling algorithm (CFS) used for user processes. The CFS employs a red-black tree to manage tasks based on virtual runtime, ensuring fair CPU allocation. The article also discusses practical aspects like scheduling granularity and process migration to optimize cache performance. Key topics include the initialization of new processes, the selection of appropriate CPU cores, and the context switching mechanism that enables process execution.

The article addresses two main questions: the minimum duration a process can run without yielding CPU and the role of nice values in process scheduling. It clarifies that while nice values influence CPU time allocation proportionally, they do not provide real-time preemption. The content includes code snippets demonstrating the implementation of scheduling structures and functions, such as the use of DEFINE_PER_CPU for per-CPU variables and the red-black tree operations in CFS.