As a non-system-programmer, here's my attempt in Odin.

  yes | pv > /dev/null
  0:00:15 [1.12GiB/s]
  build/yes | pv > /dev/null
  0:00:20 [1.03GiB/s]


  package main
  
  import "core:sys/linux"
  import "core:os"
  import "core:strings"
  
  main :: proc() {
    msg := "y" if len(os.args) == 1 else os.args[1]
    msg = strings.concatenate({msg, "\n"})
  
    buf := transmute([]u8) strings.repeat(msg, 8192)
    for {
      linux.write(linux.STDOUT_FILENO, buf)
    }
  }

Replace `write(..)` with `puts("y")` and you'll be an order of magnitude faster. This is due to `puts` (`printf` too) being buffered (data isn't written to term/file immediately but retained in memory until some point). Improving this process (as seen in the reddit thread) gets GNU-yes.

  yes &

A few times is still my favorite way to push a cpu to max temperature for testing. Used it a lot to detect faulty Core 2 Duo MacBook back in the day. They would short circuit some CPU sensor due to thermal expansion or melting of the wire insulation. Yes was an easy way to get the CPU’s hot enough.

If you compile your variant with -O3 I imagine it will be much faster? Iirc, the default is for GCC is to not optimise

Which implies you get pretty much 3M syscall per second. Which is a good order magnitude to know