Project 15: io_uring Echo Server

Reimplement your echo server using Linux’s io_uring interface—true asynchronous I/O with zero syscall overhead per operation. Use liburing for a cleaner API.

Quick Reference

Attribute Value
Primary Language C++
Alternative Languages C, Rust (with io-uring crate)
Difficulty Level 4: Expert
Time Estimate 2 weeks
Knowledge Area io_uring, True Async I/O, Ring Buffers
Tooling Next-generation server runtime
Prerequisites Project 9, Linux 5.10+

What You Will Build

Reimplement your echo server using Linux’s io_uring interface—true asynchronous I/O with zero syscall overhead per operation. Use liburing for a cleaner API.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Understanding ring buffers → maps to SQ (submission) and CQ (completion)
  • Submitting operations → maps to SQE preparation, submission
  • Handling completions → maps to CQE processing, chaining
  • Efficient buffer management → maps to registered buffers, buffer rings

Key Concepts

  • io_uring Fundamentals: https://unixism.net/loti/ (Lord of the io_ring)
  • liburing API: https://github.com/axboe/liburing
  • Zero-Copy I/O: io_uring and the future of async I/O - Jens Axboe (YouTube)
  • Performance Comparison: io_uring vs epoll benchmarks

Real-World Outcome

$ ./io_uring_echo_server 9000
io_uring echo server on port 9000
Ring size: 256 entries
Features: IORING_FEAT_NODROP, IORING_FEAT_SUBMIT_STABLE

# Benchmark comparison:
$ echo "Running epoll version..."
$ wrk -c 500 -t 4 -d 10 http://localhost:9001/  # epoll server
  Requests/sec: 145,000

$ echo "Running io_uring version..."
$ wrk -c 500 -t 4 -d 10 http://localhost:9000/  # io_uring server
  Requests/sec: 185,000  # ~27% faster!

# Server stats:
Submissions: 1,850,000
Completions: 1,850,000
Syscalls: 15,000  # Batched!
Ops/syscall: 123 average

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: LEARN_CPP_NETWORK_PROGRAMMING.md
  • “io_uring tutorial” by Shuveb Hussain (Lord of the io_ring)