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# Old style timekeeping
30config ARCH_USES_GETTIMEOFFSET
31	bool
32
33# The generic clock events infrastructure
34config GENERIC_CLOCKEVENTS
35	bool
36
37# Architecture can handle broadcast in a driver-agnostic way
38config ARCH_HAS_TICK_BROADCAST
39	bool
40
41# Clockevents broadcasting infrastructure
42config GENERIC_CLOCKEVENTS_BROADCAST
43	bool
44	depends on GENERIC_CLOCKEVENTS
45
46# Automatically adjust the min. reprogramming time for
47# clock event device
48config GENERIC_CLOCKEVENTS_MIN_ADJUST
49	bool
50
51# Generic update of CMOS clock
52config GENERIC_CMOS_UPDATE
53	bool
54
55if GENERIC_CLOCKEVENTS
56menu "Timers subsystem"
57
58# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
59# only related to the tick functionality. Oneshot clockevent devices
60# are supported independent of this.
61config TICK_ONESHOT
62	bool
63
64config NO_HZ_COMMON
65	bool
66	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
67	select TICK_ONESHOT
68
69choice
70	prompt "Timer tick handling"
71	default NO_HZ_IDLE if NO_HZ
72
73config HZ_PERIODIC
74	bool "Periodic timer ticks (constant rate, no dynticks)"
75	help
76	  This option keeps the tick running periodically at a constant
77	  rate, even when the CPU doesn't need it.
78
79config NO_HZ_IDLE
80	bool "Idle dynticks system (tickless idle)"
81	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
82	select NO_HZ_COMMON
83	help
84	  This option enables a tickless idle system: timer interrupts
85	  will only trigger on an as-needed basis when the system is idle.
86	  This is usually interesting for energy saving.
87
88	  Most of the time you want to say Y here.
89
90config NO_HZ_FULL
91	bool "Full dynticks system (tickless)"
92	# NO_HZ_COMMON dependency
93	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
94	# We need at least one periodic CPU for timekeeping
95	depends on SMP
96	depends on HAVE_CONTEXT_TRACKING
97	# VIRT_CPU_ACCOUNTING_GEN dependency
98	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
99	select NO_HZ_COMMON
100	select RCU_NOCB_CPU
101	select VIRT_CPU_ACCOUNTING_GEN
102	select IRQ_WORK
103	select CPU_ISOLATION
104	help
105	 Adaptively try to shutdown the tick whenever possible, even when
106	 the CPU is running tasks. Typically this requires running a single
107	 task on the CPU. Chances for running tickless are maximized when
108	 the task mostly runs in userspace and has few kernel activity.
109
110	 You need to fill up the nohz_full boot parameter with the
111	 desired range of dynticks CPUs.
112
113	 This is implemented at the expense of some overhead in user <-> kernel
114	 transitions: syscalls, exceptions and interrupts. Even when it's
115	 dynamically off.
116
117	 Say N.
118
119endchoice
120
121config CONTEXT_TRACKING
122       bool
123
124config CONTEXT_TRACKING_FORCE
125	bool "Force context tracking"
126	depends on CONTEXT_TRACKING
127	default y if !NO_HZ_FULL
128	help
129	  The major pre-requirement for full dynticks to work is to
130	  support the context tracking subsystem. But there are also
131	  other dependencies to provide in order to make the full
132	  dynticks working.
133
134	  This option stands for testing when an arch implements the
135	  context tracking backend but doesn't yet fullfill all the
136	  requirements to make the full dynticks feature working.
137	  Without the full dynticks, there is no way to test the support
138	  for context tracking and the subsystems that rely on it: RCU
139	  userspace extended quiescent state and tickless cputime
140	  accounting. This option copes with the absence of the full
141	  dynticks subsystem by forcing the context tracking on all
142	  CPUs in the system.
143
144	  Say Y only if you're working on the development of an
145	  architecture backend for the context tracking.
146
147	  Say N otherwise, this option brings an overhead that you
148	  don't want in production.
149
150config NO_HZ
151	bool "Old Idle dynticks config"
152	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
153	help
154	  This is the old config entry that enables dynticks idle.
155	  We keep it around for a little while to enforce backward
156	  compatibility with older config files.
157
158config HIGH_RES_TIMERS
159	bool "High Resolution Timer Support"
160	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
161	select TICK_ONESHOT
162	help
163	  This option enables high resolution timer support. If your
164	  hardware is not capable then this option only increases
165	  the size of the kernel image.
166
167endmenu
168endif
169