Not impressive at all. Basically he had to write a lot of manual buffering code to reach GNU yes throughput. I would suggest to use an infrastructure which already provides proper IO.

e.g. perl or clisp.

    $ perl -C0 -e'print "y\n" x (1024*8) while 1' | pv > /dev/null
    ^C.4GiB 0:00:11 [6.17GiB/s] [              <=>                                                     ]

    $ yes | pv > /dev/null
    ^C.3GiB 0:00:07 [6.64GiB/s] [         <=>

And with linux-only vmsplice the record stands at 123GB/s https://www.reddit.com/r/unix/comments/6gxduc/how_is_gnu_yes...