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 # Timekeeping vsyscall support
21 config GENERIC_TIME_VSYSCALL
24 # The generic clock events infrastructure
25 config GENERIC_CLOCKEVENTS
26 def_bool !LEGACY_TIMER_TICK
28 # Architecture can handle broadcast in a driver-agnostic way
29 config ARCH_HAS_TICK_BROADCAST
32 # Clockevents broadcasting infrastructure
33 config GENERIC_CLOCKEVENTS_BROADCAST
35 depends on GENERIC_CLOCKEVENTS
37 # Handle broadcast in default_idle_call()
38 config GENERIC_CLOCKEVENTS_BROADCAST_IDLE
40 depends on GENERIC_CLOCKEVENTS_BROADCAST
42 # Automatically adjust the min. reprogramming time for
44 config GENERIC_CLOCKEVENTS_MIN_ADJUST
47 # Generic update of CMOS clock
48 config GENERIC_CMOS_UPDATE
51 # Select to handle posix CPU timers from task_work
52 # and not from the timer interrupt context
53 config HAVE_POSIX_CPU_TIMERS_TASK_WORK
56 config POSIX_CPU_TIMERS_TASK_WORK
58 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
60 config LEGACY_TIMER_TICK
63 The legacy timer tick helper is used by platforms that
64 lack support for the generic clockevent framework.
65 New platforms should use generic clockevents instead.
67 config TIME_KUNIT_TEST
68 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
70 default KUNIT_ALL_TESTS
72 Enable this option to test RTC library functions.
76 config CONTEXT_TRACKING
79 config CONTEXT_TRACKING_IDLE
81 select CONTEXT_TRACKING
83 Tracks idle state on behalf of RCU.
85 if GENERIC_CLOCKEVENTS
86 menu "Timers subsystem"
88 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
89 # only related to the tick functionality. Oneshot clockevent devices
90 # are supported independent of this.
99 prompt "Timer tick handling"
100 default NO_HZ_IDLE if NO_HZ
103 bool "Periodic timer ticks (constant rate, no dynticks)"
105 This option keeps the tick running periodically at a constant
106 rate, even when the CPU doesn't need it.
109 bool "Idle dynticks system (tickless idle)"
112 This option enables a tickless idle system: timer interrupts
113 will only trigger on an as-needed basis when the system is idle.
114 This is usually interesting for energy saving.
116 Most of the time you want to say Y here.
119 bool "Full dynticks system (tickless)"
120 # NO_HZ_COMMON dependency
121 # We need at least one periodic CPU for timekeeping
123 depends on HAVE_CONTEXT_TRACKING_USER
124 # VIRT_CPU_ACCOUNTING_GEN dependency
125 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
128 select VIRT_CPU_ACCOUNTING_GEN
132 Adaptively try to shutdown the tick whenever possible, even when
133 the CPU is running tasks. Typically this requires running a single
134 task on the CPU. Chances for running tickless are maximized when
135 the task mostly runs in userspace and has few kernel activity.
137 You need to fill up the nohz_full boot parameter with the
138 desired range of dynticks CPUs to use it. This is implemented at
139 the expense of some overhead in user <-> kernel transitions:
140 syscalls, exceptions and interrupts.
142 By default, without passing the nohz_full parameter, this behaves just
145 If you're a distro say Y.
149 config CONTEXT_TRACKING_USER
151 depends on HAVE_CONTEXT_TRACKING_USER
152 select CONTEXT_TRACKING
154 Track transitions between kernel and user on behalf of RCU and
155 tickless cputime accounting. The former case relies on context
156 tracking to enter/exit RCU extended quiescent states.
158 config CONTEXT_TRACKING_USER_FORCE
159 bool "Force user context tracking"
160 depends on CONTEXT_TRACKING_USER
161 default y if !NO_HZ_FULL
163 The major pre-requirement for full dynticks to work is to
164 support the user context tracking subsystem. But there are also
165 other dependencies to provide in order to make the full
168 This option stands for testing when an arch implements the
169 user context tracking backend but doesn't yet fulfill all the
170 requirements to make the full dynticks feature working.
171 Without the full dynticks, there is no way to test the support
172 for user context tracking and the subsystems that rely on it: RCU
173 userspace extended quiescent state and tickless cputime
174 accounting. This option copes with the absence of the full
175 dynticks subsystem by forcing the user context tracking on all
178 Say Y only if you're working on the development of an
179 architecture backend for the user context tracking.
181 Say N otherwise, this option brings an overhead that you
182 don't want in production.
185 bool "Old Idle dynticks config"
187 This is the old config entry that enables dynticks idle.
188 We keep it around for a little while to enforce backward
189 compatibility with older config files.
191 config HIGH_RES_TIMERS
192 bool "High Resolution Timer Support"
195 This option enables high resolution timer support. If your
196 hardware is not capable then this option only increases
197 the size of the kernel image.
199 config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
200 int "Clocksource watchdog maximum allowable skew (in microseconds)"
201 depends on CLOCKSOURCE_WATCHDOG
205 Specify the maximum amount of allowable watchdog skew in
206 microseconds before reporting the clocksource to be unstable.
207 The default is based on a half-second clocksource watchdog
208 interval and NTP's maximum frequency drift of 500 parts
209 per million. If the clocksource is good enough for NTP,
210 it is good enough for the clocksource watchdog!