1. There is no implementation of a clock timer on ARM 32 and ARM 64 machines.
Aleksey Kopytov proposed a patch for ARM 64:
https://bugs.mysql.com/bug.php?id=77620 (which is already in MySQL sources),
as well as gave a link to the implementation in Linux kernel:
http://lxr.free-electrons.com/ident?v=3.10;i=arch_counter_get_cntvct
(we can search for a version for ARM 32 and other missing platforms).

2. In case when during initialization on timers at mysqld startup the resolution of a cycler time appears to be worse than a nanosecond, mysqld should probably switch the "wait" events to use the nanosecond timer by default.