alt Hacker NewsWow, I am somewhat ashamed to admin that I had never heard of "xv6" until your comment! I found the MIT homepage here: https://pdos.csail.mit.edu/6.1810/2024/xv6.html
Two things standout to me: (1) It was written in 2006. RISC V was not released until 2010 (so says Google). I guess it was ported from x86? (2) Russ Cox is one of the contacts listed on MIT homepage. That guy's digital footprints are enormous.
Yes, it was ported from x86. And no, xv6 is not really an OS you want to use in production. There are a lot of design decisions that optimize for pedagogy instead of performance or even reliability (e.g. the kernel is more than happy to panic if/when you get off the "intended path").