while true do
      io.write "1"
    end

PUC-Rio 5.4: 25 MiB/s

LuaJIT 2.1.0-beta3: 550 MiB/s <--- WOW

They all go slightly faster if you localize the reference to `io.write`

    local write = io.write
    while true do
      write "1"
    end