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1# SPDX-License-Identifier: GPL-2.0-only
2#
3# Timer subsystem related configuration options
4#
5
6# Options selectable by arch Kconfig
7
8# Watchdog function for clocksources to detect instabilities
9config CLOCKSOURCE_WATCHDOG
10 bool
11
12# Architecture has extra clocksource init called from registration
13config ARCH_CLOCKSOURCE_INIT
14 bool
15
16config ARCH_WANTS_CLOCKSOURCE_READ_INLINE
17 bool
18
19# The generic clock events infrastructure
20config GENERIC_CLOCKEVENTS
21 def_bool !LEGACY_TIMER_TICK
22
23# Architecture can handle broadcast in a driver-agnostic way
24config ARCH_HAS_TICK_BROADCAST
25 bool
26
27# Clockevents broadcasting infrastructure
28config GENERIC_CLOCKEVENTS_BROADCAST
29 bool
30 depends on GENERIC_CLOCKEVENTS
31
32# Handle broadcast in default_idle_call()
33config GENERIC_CLOCKEVENTS_BROADCAST_IDLE
34 bool
35 depends on GENERIC_CLOCKEVENTS_BROADCAST
36
37# Automatically adjust the min. reprogramming time for
38# clock event device
39config GENERIC_CLOCKEVENTS_MIN_ADJUST
40 bool
41
42config GENERIC_CLOCKEVENTS_COUPLED
43 bool
44
45config GENERIC_CLOCKEVENTS_COUPLED_INLINE
46 select GENERIC_CLOCKEVENTS_COUPLED
47 bool
48
49# Generic update of CMOS clock
50config GENERIC_CMOS_UPDATE
51 bool
52
53# Deferred rearming of the hrtimer interrupt
54config HRTIMER_REARM_DEFERRED
55 def_bool y
56 depends on GENERIC_ENTRY && HAVE_GENERIC_TIF_BITS
57 depends on HIGH_RES_TIMERS && SCHED_HRTICK
58
59# Select to handle posix CPU timers from task_work
60# and not from the timer interrupt context
61config HAVE_POSIX_CPU_TIMERS_TASK_WORK
62 bool
63
64config POSIX_CPU_TIMERS_TASK_WORK
65 bool
66 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
67
68config LEGACY_TIMER_TICK
69 bool
70 help
71 The legacy timer tick helper is used by platforms that
72 lack support for the generic clockevent framework.
73 New platforms should use generic clockevents instead.
74
75config TIME_KUNIT_TEST
76 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
77 depends on KUNIT
78 default KUNIT_ALL_TESTS
79 help
80 Enable this option to test RTC library functions.
81
82 If unsure, say N.
83
84config CONTEXT_TRACKING
85 bool
86
87config CONTEXT_TRACKING_IDLE
88 bool
89 select CONTEXT_TRACKING
90 help
91 Tracks idle state on behalf of RCU.
92
93menu "Timers subsystem"
94
95if GENERIC_CLOCKEVENTS
96# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
97# only related to the tick functionality. Oneshot clockevent devices
98# are supported independent of this.
99config TICK_ONESHOT
100 bool
101
102config NO_HZ_COMMON
103 bool
104 select TICK_ONESHOT
105
106choice
107 prompt "Timer tick handling"
108 default NO_HZ_IDLE if NO_HZ
109
110config HZ_PERIODIC
111 bool "Periodic timer ticks (constant rate, no dynticks)"
112 help
113 This option keeps the tick running periodically at a constant
114 rate, even when the CPU doesn't need it.
115
116config NO_HZ_IDLE
117 bool "Idle dynticks system (tickless idle)"
118 select NO_HZ_COMMON
119 help
120 This option enables a tickless idle system: timer interrupts
121 will only trigger on an as-needed basis when the system is idle.
122 This is usually interesting for energy saving.
123
124 Most of the time you want to say Y here.
125
126config NO_HZ_FULL
127 bool "Full dynticks system (tickless)"
128 # NO_HZ_COMMON dependency
129 # We need at least one periodic CPU for timekeeping
130 depends on SMP
131 depends on HAVE_CONTEXT_TRACKING_USER
132 # VIRT_CPU_ACCOUNTING_GEN dependency
133 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
134 select NO_HZ_COMMON
135 select RCU_NOCB_CPU
136 select IRQ_WORK
137 select CPU_ISOLATION
138 help
139 Adaptively try to shutdown the tick whenever possible, even when
140 the CPU is running tasks. Typically this requires running a single
141 task on the CPU. Chances for running tickless are maximized when
142 the task mostly runs in userspace and has few kernel activity.
143
144 You need to fill up the nohz_full boot parameter with the
145 desired range of dynticks CPUs to use it. This is implemented at
146 the expense of some overhead in user <-> kernel transitions:
147 syscalls, exceptions and interrupts.
148
149 By default, without passing the nohz_full parameter, this behaves just
150 like NO_HZ_IDLE.
151
152 If you're a distro say Y.
153
154endchoice
155
156config CONTEXT_TRACKING_USER
157 bool
158 depends on HAVE_CONTEXT_TRACKING_USER
159 select CONTEXT_TRACKING
160 help
161 Track transitions between kernel and user on behalf of RCU and
162 tickless cputime accounting. The former case relies on context
163 tracking to enter/exit RCU extended quiescent states.
164
165config CONTEXT_TRACKING_USER_FORCE
166 bool "Force user context tracking"
167 depends on CONTEXT_TRACKING_USER
168 default y if !NO_HZ_FULL
169 help
170 The major pre-requirement for full dynticks to work is to
171 support the user context tracking subsystem. But there are also
172 other dependencies to provide in order to make the full
173 dynticks working.
174
175 This option stands for testing when an arch implements the
176 user context tracking backend but doesn't yet fulfill all the
177 requirements to make the full dynticks feature working.
178 Without the full dynticks, there is no way to test the support
179 for user context tracking and the subsystems that rely on it: RCU
180 userspace extended quiescent state and tickless cputime
181 accounting. This option copes with the absence of the full
182 dynticks subsystem by forcing the user context tracking on all
183 CPUs in the system.
184
185 Say Y only if you're working on the development of an
186 architecture backend for the user context tracking.
187
188 Say N otherwise, this option brings an overhead that you
189 don't want in production.
190
191config NO_HZ
192 bool "Old Idle dynticks config"
193 help
194 This is the old config entry that enables dynticks idle.
195 We keep it around for a little while to enforce backward
196 compatibility with older config files.
197
198config HIGH_RES_TIMERS
199 bool "High Resolution Timer Support"
200 select TICK_ONESHOT
201 help
202 This option enables high resolution timer support. If your
203 hardware is not capable then this option only increases
204 the size of the kernel image.
205
206endif
207
208config POSIX_AUX_CLOCKS
209 bool "Enable auxiliary POSIX clocks"
210 depends on POSIX_TIMERS
211 help
212 Auxiliary POSIX clocks are clocks which can be steered
213 independently of the core timekeeper, which controls the
214 MONOTONIC, REALTIME, BOOTTIME and TAI clocks. They are useful to
215 provide e.g. lockless time accessors to independent PTP clocks
216 and other clock domains, which are not correlated to the TAI/NTP
217 notion of time.
218
219endmenu