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 data
13config ARCH_CLOCKSOURCE_DATA
14	bool
15
16# Architecture has extra clocksource init called from registration
17config ARCH_CLOCKSOURCE_INIT
18	bool
19
20# Clocksources require validation of the clocksource against the last
21# cycle update - x86/TSC misfeature
22config CLOCKSOURCE_VALIDATE_LAST_CYCLE
23	bool
24
25# Timekeeping vsyscall support
26config GENERIC_TIME_VSYSCALL
27	bool
28
29# The generic clock events infrastructure
30config GENERIC_CLOCKEVENTS
31	def_bool !LEGACY_TIMER_TICK
32
33# Architecture can handle broadcast in a driver-agnostic way
34config ARCH_HAS_TICK_BROADCAST
35	bool
36
37# Clockevents broadcasting infrastructure
38config GENERIC_CLOCKEVENTS_BROADCAST
39	bool
40	depends on GENERIC_CLOCKEVENTS
41
42# Automatically adjust the min. reprogramming time for
43# clock event device
44config GENERIC_CLOCKEVENTS_MIN_ADJUST
45	bool
46
47# Generic update of CMOS clock
48config GENERIC_CMOS_UPDATE
49	bool
50
51# Select to handle posix CPU timers from task_work
52# and not from the timer interrupt context
53config HAVE_POSIX_CPU_TIMERS_TASK_WORK
54	bool
55
56config POSIX_CPU_TIMERS_TASK_WORK
57	bool
58	default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
59
60config LEGACY_TIMER_TICK
61	bool
62	help
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.
66
67config TIME_KUNIT_TEST
68	tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
69	depends on KUNIT
70	default KUNIT_ALL_TESTS
71	help
72	  Enable this option to test RTC library functions.
73
74	  If unsure, say N.
75
76if GENERIC_CLOCKEVENTS
77menu "Timers subsystem"
78
79# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
80# only related to the tick functionality. Oneshot clockevent devices
81# are supported independent of this.
82config TICK_ONESHOT
83	bool
84
85config NO_HZ_COMMON
86	bool
87	select TICK_ONESHOT
88
89choice
90	prompt "Timer tick handling"
91	default NO_HZ_IDLE if NO_HZ
92
93config HZ_PERIODIC
94	bool "Periodic timer ticks (constant rate, no dynticks)"
95	help
96	  This option keeps the tick running periodically at a constant
97	  rate, even when the CPU doesn't need it.
98
99config NO_HZ_IDLE
100	bool "Idle dynticks system (tickless idle)"
101	select NO_HZ_COMMON
102	help
103	  This option enables a tickless idle system: timer interrupts
104	  will only trigger on an as-needed basis when the system is idle.
105	  This is usually interesting for energy saving.
106
107	  Most of the time you want to say Y here.
108
109config NO_HZ_FULL
110	bool "Full dynticks system (tickless)"
111	# NO_HZ_COMMON dependency
112	# We need at least one periodic CPU for timekeeping
113	depends on SMP
114	depends on HAVE_CONTEXT_TRACKING
115	# VIRT_CPU_ACCOUNTING_GEN dependency
116	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
117	select NO_HZ_COMMON
118	select RCU_NOCB_CPU
119	select VIRT_CPU_ACCOUNTING_GEN
120	select IRQ_WORK
121	select CPU_ISOLATION
122	help
123	 Adaptively try to shutdown the tick whenever possible, even when
124	 the CPU is running tasks. Typically this requires running a single
125	 task on the CPU. Chances for running tickless are maximized when
126	 the task mostly runs in userspace and has few kernel activity.
127
128	 You need to fill up the nohz_full boot parameter with the
129	 desired range of dynticks CPUs to use it. This is implemented at
130	 the expense of some overhead in user <-> kernel transitions:
131	 syscalls, exceptions and interrupts.
132
133	 By default, without passing the nohz_full parameter, this behaves just
134	 like NO_HZ_IDLE.
135
136	 If you're a distro say Y.
137
138endchoice
139
140config CONTEXT_TRACKING
141       bool
142
143config CONTEXT_TRACKING_FORCE
144	bool "Force context tracking"
145	depends on CONTEXT_TRACKING
146	default y if !NO_HZ_FULL
147	help
148	  The major pre-requirement for full dynticks to work is to
149	  support the context tracking subsystem. But there are also
150	  other dependencies to provide in order to make the full
151	  dynticks working.
152
153	  This option stands for testing when an arch implements the
154	  context tracking backend but doesn't yet fulfill all the
155	  requirements to make the full dynticks feature working.
156	  Without the full dynticks, there is no way to test the support
157	  for context tracking and the subsystems that rely on it: RCU
158	  userspace extended quiescent state and tickless cputime
159	  accounting. This option copes with the absence of the full
160	  dynticks subsystem by forcing the context tracking on all
161	  CPUs in the system.
162
163	  Say Y only if you're working on the development of an
164	  architecture backend for the context tracking.
165
166	  Say N otherwise, this option brings an overhead that you
167	  don't want in production.
168
169config NO_HZ
170	bool "Old Idle dynticks config"
171	help
172	  This is the old config entry that enables dynticks idle.
173	  We keep it around for a little while to enforce backward
174	  compatibility with older config files.
175
176config HIGH_RES_TIMERS
177	bool "High Resolution Timer Support"
178	select TICK_ONESHOT
179	help
180	  This option enables high resolution timer support. If your
181	  hardware is not capable then this option only increases
182	  the size of the kernel image.
183
184endmenu
185endif
186