NetBSD configures a timer device to deliver a periodic timer interrupt, usually every 10 ms, in order to count time, wake threads that are sleeping, etc. This made sense when timer devices were expensive to program and CPUs ran at MHz. But today, CPUs run at GHz; timers on modern x86, arm, mips, etc. hardware are cheap to reprogram; programs expect greater than 10 ms resolution for sleep times; and mandatory periodic activity on idle machines wastes power.
There are three main miletones to this project:
Design a machine-independent high-resolution timer API, implement it on a couple machines, and develop tests to confirm that it works, in order to enable high-resolution sleeps.
Convert all the functions of the periodic 10 ms timer, `hardclock', to schedule activity only when needed.
Convert the various software subsystems that rely on periodic timer interrupts every tick, or every second, via callouts, either to avoid periodic work altogether, or to batch it up only when the machine is about to go idle, in order to reduce the number of wakeups and thereby reduce power consumption.