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
55# Select to handle posix CPU timers from task_work
56# and not from the timer interrupt context
57config HAVE_POSIX_CPU_TIMERS_TASK_WORK
58	bool
59
60config POSIX_CPU_TIMERS_TASK_WORK
61	bool
62	default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
63
64if GENERIC_CLOCKEVENTS
65menu "Timers subsystem"
66
67# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
68# only related to the tick functionality. Oneshot clockevent devices
69# are supported independent of this.
70config TICK_ONESHOT
71	bool
72
73config NO_HZ_COMMON
74	bool
75	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
76	select TICK_ONESHOT
77
78choice
79	prompt "Timer tick handling"
80	default NO_HZ_IDLE if NO_HZ
81
82config HZ_PERIODIC
83	bool "Periodic timer ticks (constant rate, no dynticks)"
84	help
85	  This option keeps the tick running periodically at a constant
86	  rate, even when the CPU doesn't need it.
87
88config NO_HZ_IDLE
89	bool "Idle dynticks system (tickless idle)"
90	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
91	select NO_HZ_COMMON
92	help
93	  This option enables a tickless idle system: timer interrupts
94	  will only trigger on an as-needed basis when the system is idle.
95	  This is usually interesting for energy saving.
96
97	  Most of the time you want to say Y here.
98
99config NO_HZ_FULL
100	bool "Full dynticks system (tickless)"
101	# NO_HZ_COMMON dependency
102	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
103	# We need at least one periodic CPU for timekeeping
104	depends on SMP
105	depends on HAVE_CONTEXT_TRACKING
106	# VIRT_CPU_ACCOUNTING_GEN dependency
107	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
108	select NO_HZ_COMMON
109	select RCU_NOCB_CPU
110	select VIRT_CPU_ACCOUNTING_GEN
111	select IRQ_WORK
112	select CPU_ISOLATION
113	help
114	 Adaptively try to shutdown the tick whenever possible, even when
115	 the CPU is running tasks. Typically this requires running a single
116	 task on the CPU. Chances for running tickless are maximized when
117	 the task mostly runs in userspace and has few kernel activity.
118
119	 You need to fill up the nohz_full boot parameter with the
120	 desired range of dynticks CPUs.
121
122	 This is implemented at the expense of some overhead in user <-> kernel
123	 transitions: syscalls, exceptions and interrupts. Even when it's
124	 dynamically off.
125
126	 Say N.
127
128endchoice
129
130config CONTEXT_TRACKING
131       bool
132
133config CONTEXT_TRACKING_FORCE
134	bool "Force context tracking"
135	depends on CONTEXT_TRACKING
136	default y if !NO_HZ_FULL
137	help
138	  The major pre-requirement for full dynticks to work is to
139	  support the context tracking subsystem. But there are also
140	  other dependencies to provide in order to make the full
141	  dynticks working.
142
143	  This option stands for testing when an arch implements the
144	  context tracking backend but doesn't yet fullfill all the
145	  requirements to make the full dynticks feature working.
146	  Without the full dynticks, there is no way to test the support
147	  for context tracking and the subsystems that rely on it: RCU
148	  userspace extended quiescent state and tickless cputime
149	  accounting. This option copes with the absence of the full
150	  dynticks subsystem by forcing the context tracking on all
151	  CPUs in the system.
152
153	  Say Y only if you're working on the development of an
154	  architecture backend for the context tracking.
155
156	  Say N otherwise, this option brings an overhead that you
157	  don't want in production.
158
159config NO_HZ
160	bool "Old Idle dynticks config"
161	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
162	help
163	  This is the old config entry that enables dynticks idle.
164	  We keep it around for a little while to enforce backward
165	  compatibility with older config files.
166
167config HIGH_RES_TIMERS
168	bool "High Resolution Timer Support"
169	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
170	select TICK_ONESHOT
171	help
172	  This option enables high resolution timer support. If your
173	  hardware is not capable then this option only increases
174	  the size of the kernel image.
175
176endmenu
177endif
178