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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# Timekeeping vsyscall support
16config GENERIC_TIME_VSYSCALL
17 bool
18
19# Timekeeping vsyscall support
20config GENERIC_TIME_VSYSCALL_OLD
21 bool
22
23# ktime_t scalar 64bit nsec representation
24config KTIME_SCALAR
25 bool
26
27# Old style timekeeping
28config ARCH_USES_GETTIMEOFFSET
29 bool
30
31# The generic clock events infrastructure
32config GENERIC_CLOCKEVENTS
33 bool
34
35# Migration helper. Builds, but does not invoke
36config GENERIC_CLOCKEVENTS_BUILD
37 bool
38 default y
39 depends on GENERIC_CLOCKEVENTS
40
41# Architecture can handle broadcast in a driver-agnostic way
42config ARCH_HAS_TICK_BROADCAST
43 bool
44
45# Clockevents broadcasting infrastructure
46config GENERIC_CLOCKEVENTS_BROADCAST
47 bool
48 depends on GENERIC_CLOCKEVENTS
49
50# Automatically adjust the min. reprogramming time for
51# clock event device
52config GENERIC_CLOCKEVENTS_MIN_ADJUST
53 bool
54
55# Generic update of CMOS clock
56config GENERIC_CMOS_UPDATE
57 bool
58
59if GENERIC_CLOCKEVENTS
60menu "Timers subsystem"
61
62# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
63# only related to the tick functionality. Oneshot clockevent devices
64# are supported independ of this.
65config TICK_ONESHOT
66 bool
67
68config NO_HZ_COMMON
69 bool
70 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
71 select TICK_ONESHOT
72
73choice
74 prompt "Timer tick handling"
75 default NO_HZ_IDLE if NO_HZ
76
77config HZ_PERIODIC
78 bool "Periodic timer ticks (constant rate, no dynticks)"
79 help
80 This option keeps the tick running periodically at a constant
81 rate, even when the CPU doesn't need it.
82
83config NO_HZ_IDLE
84 bool "Idle dynticks system (tickless idle)"
85 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
86 select NO_HZ_COMMON
87 help
88 This option enables a tickless idle system: timer interrupts
89 will only trigger on an as-needed basis when the system is idle.
90 This is usually interesting for energy saving.
91
92 Most of the time you want to say Y here.
93
94config NO_HZ_FULL
95 bool "Full dynticks system (tickless)"
96 # NO_HZ_COMMON dependency
97 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
98 # We need at least one periodic CPU for timekeeping
99 depends on SMP
100 # RCU_USER_QS dependency
101 depends on HAVE_CONTEXT_TRACKING
102 # VIRT_CPU_ACCOUNTING_GEN dependency
103 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
104 select NO_HZ_COMMON
105 select RCU_USER_QS
106 select RCU_NOCB_CPU
107 select VIRT_CPU_ACCOUNTING_GEN
108 select IRQ_WORK
109 help
110 Adaptively try to shutdown the tick whenever possible, even when
111 the CPU is running tasks. Typically this requires running a single
112 task on the CPU. Chances for running tickless are maximized when
113 the task mostly runs in userspace and has few kernel activity.
114
115 You need to fill up the nohz_full boot parameter with the
116 desired range of dynticks CPUs.
117
118 This is implemented at the expense of some overhead in user <-> kernel
119 transitions: syscalls, exceptions and interrupts. Even when it's
120 dynamically off.
121
122 Say N.
123
124endchoice
125
126config NO_HZ_FULL_ALL
127 bool "Full dynticks system on all CPUs by default (except CPU 0)"
128 depends on NO_HZ_FULL
129 help
130 If the user doesn't pass the nohz_full boot option to
131 define the range of full dynticks CPUs, consider that all
132 CPUs in the system are full dynticks by default.
133 Note the boot CPU will still be kept outside the range to
134 handle the timekeeping duty.
135
136config NO_HZ_FULL_SYSIDLE
137 bool "Detect full-system idle state for full dynticks system"
138 depends on NO_HZ_FULL
139 default n
140 help
141 At least one CPU must keep the scheduling-clock tick running for
142 timekeeping purposes whenever there is a non-idle CPU, where
143 "non-idle" also includes dynticks CPUs as long as they are
144 running non-idle tasks. Because the underlying adaptive-tick
145 support cannot distinguish between all CPUs being idle and
146 all CPUs each running a single task in dynticks mode, the
147 underlying support simply ensures that there is always a CPU
148 handling the scheduling-clock tick, whether or not all CPUs
149 are idle. This Kconfig option enables scalable detection of
150 the all-CPUs-idle state, thus allowing the scheduling-clock
151 tick to be disabled when all CPUs are idle. Note that scalable
152 detection of the all-CPUs-idle state means that larger systems
153 will be slower to declare the all-CPUs-idle state.
154
155 Say Y if you would like to help debug all-CPUs-idle detection.
156
157 Say N if you are unsure.
158
159config NO_HZ_FULL_SYSIDLE_SMALL
160 int "Number of CPUs above which large-system approach is used"
161 depends on NO_HZ_FULL_SYSIDLE
162 range 1 NR_CPUS
163 default 8
164 help
165 The full-system idle detection mechanism takes a lazy approach
166 on large systems, as is required to attain decent scalability.
167 However, on smaller systems, scalability is not anywhere near as
168 large a concern as is energy efficiency. The sysidle subsystem
169 therefore uses a fast but non-scalable algorithm for small
170 systems and a lazier but scalable algorithm for large systems.
171 This Kconfig parameter defines the number of CPUs in the largest
172 system that will be considered to be "small".
173
174 The default value will be fine in most cases. Battery-powered
175 systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
176 numbers of CPUs, and (3) are suffering from battery-lifetime
177 problems due to long sysidle latencies might wish to experiment
178 with larger values for this Kconfig parameter. On the other
179 hand, they might be even better served by disabling NO_HZ_FULL
180 entirely, given that NO_HZ_FULL is intended for HPC and
181 real-time workloads that at present do not tend to be run on
182 battery-powered systems.
183
184 Take the default if you are unsure.
185
186config NO_HZ
187 bool "Old Idle dynticks config"
188 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
189 help
190 This is the old config entry that enables dynticks idle.
191 We keep it around for a little while to enforce backward
192 compatibility with older config files.
193
194config HIGH_RES_TIMERS
195 bool "High Resolution Timer Support"
196 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
197 select TICK_ONESHOT
198 help
199 This option enables high resolution timer support. If your
200 hardware is not capable then this option only increases
201 the size of the kernel image.
202
203endmenu
204endif
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