I saw 100% I/O wait in htop today but couldn’t find a process which actually does I/O. Turns out, I/O wait isn’t what it used to be anymore:

https://lwn.net/Articles/989272/

In my case, it was mpd which triggered this:

https://github.com/MusicPlayerDaemon/MPD/issues/2241

mpd doesn’t actually do anything, it just sits there and waits for events. To my understanding, this is similar to something blocking on read(). I’m not quite sure yet if displaying this as I/O wait (or “PSI some io”) is intentional or not – but it sure is confusing.