If you're using btrfs and its snapshot function: stay away from kernel 3.17! It may corrupt your filesystem. I've just spent the better part of the morning trying to coax my desktop into getting back to its normal self.
After updating to 3.17 and editing syslinux.cfg to take care of the now manual microcode updates, I've noticed the following anomalies:
- KDE needed several minutes to start, just as every KDE application afterwards
- System load was high (up to 5) despite the fact that the system was essentially idling (no CPU or I/O activities)
- the btrfs formatted system partition switched to RO mode after a few minutes of use. WTF?
- after a further reboot with the microcode updates disabled, avahi didn't come up and journald dumped one core after the other (105, to be precise).
- oh, and there was no network at this point :/
After rolling back to kernel 3.16.4, reinstalling systemd, and purging all (corrupted) journal files in /var/log/journal, the worst seems to be over.
Note that this bug is not restricted to users of Archlinux, but was reported by users of Fedora 20, Debian Sid, Gentoo, and OpenSUSE Tumbleweed.