And also user defined events and timers(through the new thread pool API)
Granted libaio only really works well on XFS [3], and even there it has issues.
[0] - https://lwn.net/Articles/251413/
[1] - http://man7.org/linux/man-pages/man2/eventfd.2.html
[2] - https://www.fsl.cs.sunysb.edu/~vass/linux-aio.txt
[3] - http://www.scylladb.com/2016/02/09/qualifying-filesystems/