Documentation/timers/no_hz.rst

2 NO_HZ: Reducing Scheduling-Clock Ticks
13 (also known as "scheduling-clock ticks" or simply "ticks"):
15 1.	Never omit scheduling-clock ticks (CONFIG_HZ_PERIODIC=y or
19 2.	Omit scheduling-clock ticks on idle CPUs (CONFIG_NO_HZ_IDLE=y or
23 3.	Omit scheduling-clock ticks on CPUs that are either idle or that
33 Never Omit Scheduling-Clock Ticks
37 are incapable of omitting scheduling-clock ticks.  It turns out that
65 Omit Scheduling-Clock Ticks For Idle CPUs
104 Omit Scheduling-Clock Ticks For CPUs With Only One Runnable Task
109 Note that omitting scheduling-clock ticks for CPUs with only one runnable
114 and such CPUs are said to be "adaptive-ticks CPUs".  This is important
124 By default, no CPU will be an adaptive-ticks CPU.  The "nohz_full="
125 boot parameter specifies the adaptive-ticks CPUs.  For example,
126 "nohz_full=1,6-8" says that CPUs 1, 6, 7, and 8 are to be adaptive-ticks
136 Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded.
139 Normally, a CPU remains in adaptive-ticks mode as long as possible.
141 the mode.  Instead, the CPU will exit adaptive-ticks mode only if needed,
148 	adaptive ticks without also running dyntick idle.  This dependency
171 Although improvements are expected over time, adaptive ticks is quite
173 However, the drawbacks listed above mean that adaptive ticks should not
230 	some workloads will no doubt want to use adaptive ticks to
250 *	Adaptive-ticks slows user/kernel transitions slightly.
256 *	Adaptive-ticks does not do anything unless there is only one
305 *	If there might potentially be some adaptive-ticks CPUs, there
317 	infrequent scheduling-clock ticks.