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Last Updated: June 30, 2025

io_uring: A Modern Asynchronous I/O Interface

io_uring is a modern, high-performance asynchronous I/O interface introduced in Linux kernel 5.1 (March 2019). It was designed to significantly improve I/O efficiency for high-throughput, low-latency applications such as databases, file servers, filesystems, and web servers.

It provides a new Linux kernel system call interface that enables scalable, non-blocking I/O by minimizing system call overhead, context switches, and CPU usage. At its core, io_uring uses two shared ring buffers—the Submission Queue (SQ) and Completion Queue (CQ)—to manage I/O operations between user space and kernel space.

This model allows user-space programs to perform I/O with minimal syscalls, zero-copy capability, and high concurrency, addressing the limitations of older interfaces like read(), write(), aio_read(), and Linux AIO. It supports efficient asynchronous execution of file operations, socket communication, and more, making it ideal for performance-critical systems.

1. The Problem Before io_uring

Before io_uring, applications like web servers, databases, and file servers struggled to scale efficiently when handling:

• Thousands of file reads and writes
• Massive numbers of socket connections
• High-speed log operations

Traditional Linux I/O methods—such as read(), write(), epoll, select(), aio_read()—suffered from several critical drawbacks:

• Each I/O required a system call, which incurs costly context switches between user and kernel space.
• Data had to be copied between user space and kernel space, adding further latency.
• Achieving asynchronicity required complex mechanisms or user-space hacks.
• These constraints led to high CPU usage, latency spikes, and scalability bottlenecks, especially under high concurrency and throughput.