[$] Improving idle behavior in tickless systems

Most processors spend a great deal of their time doing nothing, waiting
for devices and timer interrupts. In these cases, they can switch to idle
modes that shut down parts of their internal circuitry, especially stopping
certain clocks. This lowers power consumption significantly
and avoids draining device batteries. There are usually
a number of idle modes available; the deeper the mode is, the less power the
processor needs. The tradeoff is that the cost of switching to and from
deeper modes is
higher; it takes more time and the content of some caches is also lost. In the
Linux kernel, the cpuidle subsystem has the task of predicting which choice
will be the most appropriate. Recently, Rafael Wysocki proposed
a new governor for systems with tickless operation enabled that is
expected to be more accurate than the existing menu governor.