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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 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# Handle broadcast in default_idle_call()
43config GENERIC_CLOCKEVENTS_BROADCAST_IDLE
44 bool
45 depends on GENERIC_CLOCKEVENTS_BROADCAST
46
47# Automatically adjust the min. reprogramming time for
48# clock event device
49config GENERIC_CLOCKEVENTS_MIN_ADJUST
50 bool
51
52# Generic update of CMOS clock
53config GENERIC_CMOS_UPDATE
54 bool
55
56# Select to handle posix CPU timers from task_work
57# and not from the timer interrupt context
58config HAVE_POSIX_CPU_TIMERS_TASK_WORK
59 bool
60
61config POSIX_CPU_TIMERS_TASK_WORK
62 bool
63 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
64
65config LEGACY_TIMER_TICK
66 bool
67 help
68 The legacy timer tick helper is used by platforms that
69 lack support for the generic clockevent framework.
70 New platforms should use generic clockevents instead.
71
72config TIME_KUNIT_TEST
73 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
74 depends on KUNIT
75 default KUNIT_ALL_TESTS
76 help
77 Enable this option to test RTC library functions.
78
79 If unsure, say N.
80
81config CONTEXT_TRACKING
82 bool
83
84config CONTEXT_TRACKING_IDLE
85 bool
86 select CONTEXT_TRACKING
87 help
88 Tracks idle state on behalf of RCU.
89
90if GENERIC_CLOCKEVENTS
91menu "Timers subsystem"
92
93# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
94# only related to the tick functionality. Oneshot clockevent devices
95# are supported independent of this.
96config TICK_ONESHOT
97 bool
98
99config NO_HZ_COMMON
100 bool
101 select TICK_ONESHOT
102
103choice
104 prompt "Timer tick handling"
105 default NO_HZ_IDLE if NO_HZ
106
107config HZ_PERIODIC
108 bool "Periodic timer ticks (constant rate, no dynticks)"
109 help
110 This option keeps the tick running periodically at a constant
111 rate, even when the CPU doesn't need it.
112
113config NO_HZ_IDLE
114 bool "Idle dynticks system (tickless idle)"
115 select NO_HZ_COMMON
116 help
117 This option enables a tickless idle system: timer interrupts
118 will only trigger on an as-needed basis when the system is idle.
119 This is usually interesting for energy saving.
120
121 Most of the time you want to say Y here.
122
123config NO_HZ_FULL
124 bool "Full dynticks system (tickless)"
125 # NO_HZ_COMMON dependency
126 # We need at least one periodic CPU for timekeeping
127 depends on SMP
128 depends on HAVE_CONTEXT_TRACKING_USER
129 # VIRT_CPU_ACCOUNTING_GEN dependency
130 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
131 select NO_HZ_COMMON
132 select RCU_NOCB_CPU
133 select VIRT_CPU_ACCOUNTING_GEN
134 select IRQ_WORK
135 select CPU_ISOLATION
136 help
137 Adaptively try to shutdown the tick whenever possible, even when
138 the CPU is running tasks. Typically this requires running a single
139 task on the CPU. Chances for running tickless are maximized when
140 the task mostly runs in userspace and has few kernel activity.
141
142 You need to fill up the nohz_full boot parameter with the
143 desired range of dynticks CPUs to use it. This is implemented at
144 the expense of some overhead in user <-> kernel transitions:
145 syscalls, exceptions and interrupts.
146
147 By default, without passing the nohz_full parameter, this behaves just
148 like NO_HZ_IDLE.
149
150 If you're a distro say Y.
151
152endchoice
153
154config CONTEXT_TRACKING_USER
155 bool
156 depends on HAVE_CONTEXT_TRACKING_USER
157 select CONTEXT_TRACKING
158 help
159 Track transitions between kernel and user on behalf of RCU and
160 tickless cputime accounting. The former case relies on context
161 tracking to enter/exit RCU extended quiescent states.
162
163config CONTEXT_TRACKING_USER_FORCE
164 bool "Force user context tracking"
165 depends on CONTEXT_TRACKING_USER
166 default y if !NO_HZ_FULL
167 help
168 The major pre-requirement for full dynticks to work is to
169 support the user context tracking subsystem. But there are also
170 other dependencies to provide in order to make the full
171 dynticks working.
172
173 This option stands for testing when an arch implements the
174 user context tracking backend but doesn't yet fulfill all the
175 requirements to make the full dynticks feature working.
176 Without the full dynticks, there is no way to test the support
177 for user context tracking and the subsystems that rely on it: RCU
178 userspace extended quiescent state and tickless cputime
179 accounting. This option copes with the absence of the full
180 dynticks subsystem by forcing the user context tracking on all
181 CPUs in the system.
182
183 Say Y only if you're working on the development of an
184 architecture backend for the user context tracking.
185
186 Say N otherwise, this option brings an overhead that you
187 don't want in production.
188
189config NO_HZ
190 bool "Old Idle dynticks config"
191 help
192 This is the old config entry that enables dynticks idle.
193 We keep it around for a little while to enforce backward
194 compatibility with older config files.
195
196config HIGH_RES_TIMERS
197 bool "High Resolution Timer Support"
198 select TICK_ONESHOT
199 help
200 This option enables high resolution timer support. If your
201 hardware is not capable then this option only increases
202 the size of the kernel image.
203
204config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
205 int "Clocksource watchdog maximum allowable skew (in μs)"
206 depends on CLOCKSOURCE_WATCHDOG
207 range 50 1000
208 default 125
209 help
210 Specify the maximum amount of allowable watchdog skew in
211 microseconds before reporting the clocksource to be unstable.
212 The default is based on a half-second clocksource watchdog
213 interval and NTP's maximum frequency drift of 500 parts
214 per million. If the clocksource is good enough for NTP,
215 it is good enough for the clocksource watchdog!
216
217endmenu
218endif
1#
2# Timer subsystem related configuration options
3#
4
5# Options selectable by arch Kconfig
6
7# Watchdog function for clocksources to detect instabilities
8config CLOCKSOURCE_WATCHDOG
9 bool
10
11# Architecture has extra clocksource data
12config ARCH_CLOCKSOURCE_DATA
13 bool
14
15# Clocksources require validation of the clocksource against the last
16# cycle update - x86/TSC misfeature
17config CLOCKSOURCE_VALIDATE_LAST_CYCLE
18 bool
19
20# Timekeeping vsyscall support
21config GENERIC_TIME_VSYSCALL
22 bool
23
24# Timekeeping vsyscall support
25config GENERIC_TIME_VSYSCALL_OLD
26 bool
27
28# Old style timekeeping
29config ARCH_USES_GETTIMEOFFSET
30 bool
31
32# The generic clock events infrastructure
33config GENERIC_CLOCKEVENTS
34 bool
35
36# Architecture can handle broadcast in a driver-agnostic way
37config ARCH_HAS_TICK_BROADCAST
38 bool
39
40# Clockevents broadcasting infrastructure
41config GENERIC_CLOCKEVENTS_BROADCAST
42 bool
43 depends on GENERIC_CLOCKEVENTS
44
45# Automatically adjust the min. reprogramming time for
46# clock event device
47config GENERIC_CLOCKEVENTS_MIN_ADJUST
48 bool
49
50# Generic update of CMOS clock
51config GENERIC_CMOS_UPDATE
52 bool
53
54if GENERIC_CLOCKEVENTS
55menu "Timers subsystem"
56
57# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
58# only related to the tick functionality. Oneshot clockevent devices
59# are supported independ of this.
60config TICK_ONESHOT
61 bool
62
63config NO_HZ_COMMON
64 bool
65 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
66 select TICK_ONESHOT
67
68choice
69 prompt "Timer tick handling"
70 default NO_HZ_IDLE if NO_HZ
71
72config HZ_PERIODIC
73 bool "Periodic timer ticks (constant rate, no dynticks)"
74 help
75 This option keeps the tick running periodically at a constant
76 rate, even when the CPU doesn't need it.
77
78config NO_HZ_IDLE
79 bool "Idle dynticks system (tickless idle)"
80 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
81 select NO_HZ_COMMON
82 help
83 This option enables a tickless idle system: timer interrupts
84 will only trigger on an as-needed basis when the system is idle.
85 This is usually interesting for energy saving.
86
87 Most of the time you want to say Y here.
88
89config NO_HZ_FULL
90 bool "Full dynticks system (tickless)"
91 # NO_HZ_COMMON dependency
92 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
93 # We need at least one periodic CPU for timekeeping
94 depends on SMP
95 depends on HAVE_CONTEXT_TRACKING
96 # VIRT_CPU_ACCOUNTING_GEN dependency
97 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
98 select NO_HZ_COMMON
99 select RCU_NOCB_CPU
100 select VIRT_CPU_ACCOUNTING_GEN
101 select IRQ_WORK
102 help
103 Adaptively try to shutdown the tick whenever possible, even when
104 the CPU is running tasks. Typically this requires running a single
105 task on the CPU. Chances for running tickless are maximized when
106 the task mostly runs in userspace and has few kernel activity.
107
108 You need to fill up the nohz_full boot parameter with the
109 desired range of dynticks CPUs.
110
111 This is implemented at the expense of some overhead in user <-> kernel
112 transitions: syscalls, exceptions and interrupts. Even when it's
113 dynamically off.
114
115 Say N.
116
117endchoice
118
119config NO_HZ_FULL_ALL
120 bool "Full dynticks system on all CPUs by default (except CPU 0)"
121 depends on NO_HZ_FULL
122 help
123 If the user doesn't pass the nohz_full boot option to
124 define the range of full dynticks CPUs, consider that all
125 CPUs in the system are full dynticks by default.
126 Note the boot CPU will still be kept outside the range to
127 handle the timekeeping duty.
128
129config NO_HZ_FULL_SYSIDLE
130 bool "Detect full-system idle state for full dynticks system"
131 depends on NO_HZ_FULL
132 default n
133 help
134 At least one CPU must keep the scheduling-clock tick running for
135 timekeeping purposes whenever there is a non-idle CPU, where
136 "non-idle" also includes dynticks CPUs as long as they are
137 running non-idle tasks. Because the underlying adaptive-tick
138 support cannot distinguish between all CPUs being idle and
139 all CPUs each running a single task in dynticks mode, the
140 underlying support simply ensures that there is always a CPU
141 handling the scheduling-clock tick, whether or not all CPUs
142 are idle. This Kconfig option enables scalable detection of
143 the all-CPUs-idle state, thus allowing the scheduling-clock
144 tick to be disabled when all CPUs are idle. Note that scalable
145 detection of the all-CPUs-idle state means that larger systems
146 will be slower to declare the all-CPUs-idle state.
147
148 Say Y if you would like to help debug all-CPUs-idle detection.
149
150 Say N if you are unsure.
151
152config NO_HZ_FULL_SYSIDLE_SMALL
153 int "Number of CPUs above which large-system approach is used"
154 depends on NO_HZ_FULL_SYSIDLE
155 range 1 NR_CPUS
156 default 8
157 help
158 The full-system idle detection mechanism takes a lazy approach
159 on large systems, as is required to attain decent scalability.
160 However, on smaller systems, scalability is not anywhere near as
161 large a concern as is energy efficiency. The sysidle subsystem
162 therefore uses a fast but non-scalable algorithm for small
163 systems and a lazier but scalable algorithm for large systems.
164 This Kconfig parameter defines the number of CPUs in the largest
165 system that will be considered to be "small".
166
167 The default value will be fine in most cases. Battery-powered
168 systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
169 numbers of CPUs, and (3) are suffering from battery-lifetime
170 problems due to long sysidle latencies might wish to experiment
171 with larger values for this Kconfig parameter. On the other
172 hand, they might be even better served by disabling NO_HZ_FULL
173 entirely, given that NO_HZ_FULL is intended for HPC and
174 real-time workloads that at present do not tend to be run on
175 battery-powered systems.
176
177 Take the default if you are unsure.
178
179config NO_HZ
180 bool "Old Idle dynticks config"
181 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
182 help
183 This is the old config entry that enables dynticks idle.
184 We keep it around for a little while to enforce backward
185 compatibility with older config files.
186
187config HIGH_RES_TIMERS
188 bool "High Resolution Timer Support"
189 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
190 select TICK_ONESHOT
191 help
192 This option enables high resolution timer support. If your
193 hardware is not capable then this option only increases
194 the size of the kernel image.
195
196endmenu
197endif