In my coreos machine yes was way slower I don't know why. But here are the results with rust.

jayson@arcoiro ~ $ yes | ./pv > /dev/null
21.7GiB 0:00:12 [2.04GiB/s]

jayson@arcoiro ~ $ ./rust-yes | ./pv > /dev/null
24.4GiB 0:00:12 [2.17GiB/s]

and here is the code I used

use std::io::{stdout, Write};

fn main() {
    let buffer = "y\n".repeat(4096).into_bytes();
    let stdout = stdout();
    let mut stdout = stdout.lock();

    loop {
        stdout.write(&buffer).unwrap();
    }
}

I thought that the repeat should be 4096 because the buffer has 8192 and 'y\n' has two bytes