Re-enginer the wheel: a rejuvenation of BSD callout(9) and timer facilities

by Davide Italiano for FreeBSD

In all the BSD kernels, timers are provided using the callout(9) facility, which allows a function to be registered in order to be called at a future time. Right now, FreeBSD can't handle timeouts less then 2/HZ and precision less then 1/HZ. According to some recent tests, other OSes can do it much better. Some consumers may need better resolution, and this is important in lots of applications, e.g. allow faster TCP recovery in case of error or package loss, or real-time applications.