I forgot to mention that bfq appears to be the only IO scheduler that supports cgroups-v2
IO controllers [1]. Perhaps I am wrong, but I wasn't able to find documentation
indicating that mq-deadline is cgroup-aware, at the very least it's not documented in
the official deadline tunables section [2].
I'm mentioning this because btrfs' support for cgroups-v2 (and the IO
isolation/fairness capability it provides) was listed as one of the key reasons to move to
btrfs. While I am not clear on exactly how the IO scheduler and files system interact when
it comes to IO cgroups, I thought it was worth bringing up.
[1]
https://www.kernel.org/doc/html/latest/block/bfq-iosched.html#group-sched...
[2]
https://www.kernel.org/doc/html/latest/block/deadline-iosched.html