admin-guide/pm/cpuidle.rst

165 tick can be `stopped by the idle loop <idle-cpus-and-tick_>`_.  Available
186 .. _idle-cpus-and-tick:
188 Idle CPUs and The Scheduler Tick
191 The scheduler tick is a timer that triggers periodically in order to implement
199 may not want to give the CPU away voluntarily, however, and the scheduler tick
201 tick, but it is the primary reason for using it.
203 The scheduler tick is problematic from the CPU idle time management perspective,
205 configuration, the length of the tick period is between 1 ms and 10 ms).
206 Thus, if the tick is allowed to trigger on idle CPUs, it will not make sense
208 the tick period length.  Moreover, in that case the idle duration of any CPU
209 will never exceed the tick period length and the energy used for entering and
210 exiting idle states due to the tick wakeups on idle CPUs will be wasted.
212 Fortunately, it is not really necessary to allow the tick to trigger on idle
217 tick goes away if the given CPU is idle.  Consequently, it is possible to stop
218 the scheduler tick entirely on idle CPUs in principle, even though that may not
221 Whether or not it makes sense to stop the scheduler tick in the idle loop
223 (non-tick) timer due to trigger within the tick range, stopping the tick clearly
226 wakeup within the tick range, stopping the tick is not necessary and it may even
231 order.  Now, if the wakeup really occurs shortly, stopping the tick would be a
233 which is expensive.  On the other hand, if the tick is stopped and the wakeup
237 tick range, it is better to allow the tick trigger.  Otherwise, however, the
238 governor will select a relatively deep idle state, so the tick should be stopped
242 or not to stop the scheduler tick belongs to it.  Still, if the tick has been
246 The kernel can be configured to disable stopping the scheduler tick in the idle
250 scheduler tick is disabled, the governor's decisions regarding it are simply
251 ignored by the idle loop code and the tick is never stopped.
253 The systems that run kernels configured to allow the scheduler tick to be
256 which the tick cannot be stopped.  If the given system is tickless, it will use
273 that the scheduler tick will be stopped.  That time, referred to as the *sleep
331 if it has not decided to `stop the scheduler tick <idle-cpus-and-tick_>`_.  That
332 happens if the idle duration predicted by it is less than the tick period and
333 the tick has not been stopped already (in a previous iteration of the idle