Deep Dive: Zero-Copy Networking & io_uring

Achieving 10Gbps line-rate processing requires abandoning traditional socket programming. We explore how io_uring and zero-copy semantics redefine high-performance networking in Rust.

The Context Switch Bottleneck

In traditional Linux networking (epoll/kqueue), every read/write operation incurs a context switch between user space and kernel space. For a server handling 100,000 requests per second, these CPU cycles add up to massive latency.

Enter io_uring

io_uring creates a shared ring buffer between the kernel and user space. This allows us to submit IO requests and reap completions without incurring a syscall overhead for every operation.

use io_uring::{opcode, types, IoUring};
use std::os::unix::io::AsRawFd;

fn main() -> std::io::Result<()> {
    let mut ring = IoUring::new(8)?;
    let fd = std::fs::File::open("README.md")?;
    let mut buf = vec![0; 1024];

    let read_e = opcode::Read::new(types::Fd(fd.as_raw_fd()), buf.as_mut_ptr(), buf.len() as _)
        .build()
        .user_data(0x42);

    unsafe {
        ring.submission()
            .push(&read_e)
            .expect("submission queue is full");
    }

    ring.submit_and_wait(1)?;

    let cqe = ring.completion().next().expect("completion queue is empty");
    assert_eq!(cqe.user_data(), 0x42);
    Ok(())
}

Zero-Copy Networking

Beyond syscall reduction, we must eliminate memory copying. Standard read() copies data from the NIC buffer to the Kernel buffer, then to the User buffer. Using sendfile or splice, we can pipe data directly from disk to the socket.

In our tests, switching to a zero-copy architecture reduced CPU usage by 40% at peak load.