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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#
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