1 # SPDX-License-Identifier: GPL-2.0-only
3 # Timer subsystem related configuration options
6 # Options selectable by arch Kconfig
8 # Watchdog function for clocksources to detect instabilities
9 config CLOCKSOURCE_WATCHDOG
12 # Architecture has extra clocksource data
13 config ARCH_CLOCKSOURCE_DATA
16 # Architecture has extra clocksource init called from registration
17 config ARCH_CLOCKSOURCE_INIT
20 # Clocksources require validation of the clocksource against the last
21 # cycle update - x86/TSC misfeature
22 config CLOCKSOURCE_VALIDATE_LAST_CYCLE
25 # Timekeeping vsyscall support
26 config GENERIC_TIME_VSYSCALL
29 # The generic clock events infrastructure
30 config GENERIC_CLOCKEVENTS
31 def_bool !LEGACY_TIMER_TICK
33 # Architecture can handle broadcast in a driver-agnostic way
34 config ARCH_HAS_TICK_BROADCAST
37 # Clockevents broadcasting infrastructure
38 config GENERIC_CLOCKEVENTS_BROADCAST
40 depends on GENERIC_CLOCKEVENTS
42 # Handle broadcast in default_idle_call()
43 config GENERIC_CLOCKEVENTS_BROADCAST_IDLE
45 depends on GENERIC_CLOCKEVENTS_BROADCAST
47 # Automatically adjust the min. reprogramming time for
49 config GENERIC_CLOCKEVENTS_MIN_ADJUST
52 # Generic update of CMOS clock
53 config GENERIC_CMOS_UPDATE
56 # Select to handle posix CPU timers from task_work
57 # and not from the timer interrupt context
58 config HAVE_POSIX_CPU_TIMERS_TASK_WORK
61 config POSIX_CPU_TIMERS_TASK_WORK
63 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
65 config LEGACY_TIMER_TICK
68 The legacy timer tick helper is used by platforms that
69 lack support for the generic clockevent framework.
70 New platforms should use generic clockevents instead.
72 config TIME_KUNIT_TEST
73 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
75 default KUNIT_ALL_TESTS
77 Enable this option to test RTC library functions.
81 config CONTEXT_TRACKING
84 config CONTEXT_TRACKING_IDLE
86 select CONTEXT_TRACKING
88 Tracks idle state on behalf of RCU.
90 if GENERIC_CLOCKEVENTS
91 menu "Timers subsystem"
93 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
94 # only related to the tick functionality. Oneshot clockevent devices
95 # are supported independent of this.
104 prompt "Timer tick handling"
105 default NO_HZ_IDLE if NO_HZ
108 bool "Periodic timer ticks (constant rate, no dynticks)"
110 This option keeps the tick running periodically at a constant
111 rate, even when the CPU doesn't need it.
114 bool "Idle dynticks system (tickless idle)"
117 This option enables a tickless idle system: timer interrupts
118 will only trigger on an as-needed basis when the system is idle.
119 This is usually interesting for energy saving.
121 Most of the time you want to say Y here.
124 bool "Full dynticks system (tickless)"
125 # NO_HZ_COMMON dependency
126 # We need at least one periodic CPU for timekeeping
128 depends on HAVE_CONTEXT_TRACKING_USER
129 # VIRT_CPU_ACCOUNTING_GEN dependency
130 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
133 select VIRT_CPU_ACCOUNTING_GEN
137 Adaptively try to shutdown the tick whenever possible, even when
138 the CPU is running tasks. Typically this requires running a single
139 task on the CPU. Chances for running tickless are maximized when
140 the task mostly runs in userspace and has few kernel activity.
142 You need to fill up the nohz_full boot parameter with the
143 desired range of dynticks CPUs to use it. This is implemented at
144 the expense of some overhead in user <-> kernel transitions:
145 syscalls, exceptions and interrupts.
147 By default, without passing the nohz_full parameter, this behaves just
150 If you're a distro say Y.
154 config CONTEXT_TRACKING_USER
156 depends on HAVE_CONTEXT_TRACKING_USER
157 select CONTEXT_TRACKING
159 Track transitions between kernel and user on behalf of RCU and
160 tickless cputime accounting. The former case relies on context
161 tracking to enter/exit RCU extended quiescent states.
163 config CONTEXT_TRACKING_USER_FORCE
164 bool "Force user context tracking"
165 depends on CONTEXT_TRACKING_USER
166 default y if !NO_HZ_FULL
168 The major pre-requirement for full dynticks to work is to
169 support the user context tracking subsystem. But there are also
170 other dependencies to provide in order to make the full
173 This option stands for testing when an arch implements the
174 user context tracking backend but doesn't yet fulfill all the
175 requirements to make the full dynticks feature working.
176 Without the full dynticks, there is no way to test the support
177 for user context tracking and the subsystems that rely on it: RCU
178 userspace extended quiescent state and tickless cputime
179 accounting. This option copes with the absence of the full
180 dynticks subsystem by forcing the user context tracking on all
183 Say Y only if you're working on the development of an
184 architecture backend for the user context tracking.
186 Say N otherwise, this option brings an overhead that you
187 don't want in production.
190 bool "Old Idle dynticks config"
192 This is the old config entry that enables dynticks idle.
193 We keep it around for a little while to enforce backward
194 compatibility with older config files.
196 config HIGH_RES_TIMERS
197 bool "High Resolution Timer Support"
200 This option enables high resolution timer support. If your
201 hardware is not capable then this option only increases
202 the size of the kernel image.
204 config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
205 int "Clocksource watchdog maximum allowable skew (in microseconds)"
206 depends on CLOCKSOURCE_WATCHDOG
210 Specify the maximum amount of allowable watchdog skew in
211 microseconds before reporting the clocksource to be unstable.
212 The default is based on a half-second clocksource watchdog
213 interval and NTP's maximum frequency drift of 500 parts
214 per million. If the clocksource is good enough for NTP,
215 it is good enough for the clocksource watchdog!