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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# 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# Migration helper. Builds, but does not invoke
37config GENERIC_CLOCKEVENTS_BUILD
38	bool
39	default y
40	depends on GENERIC_CLOCKEVENTS
41
42# Architecture can handle broadcast in a driver-agnostic way
43config ARCH_HAS_TICK_BROADCAST
44	bool
45
46# Clockevents broadcasting infrastructure
47config GENERIC_CLOCKEVENTS_BROADCAST
48	bool
49	depends on GENERIC_CLOCKEVENTS
50
51# Automatically adjust the min. reprogramming time for
52# clock event device
53config GENERIC_CLOCKEVENTS_MIN_ADJUST
54	bool
55
56# Generic update of CMOS clock
57config GENERIC_CMOS_UPDATE
58	bool
59
60if GENERIC_CLOCKEVENTS
61menu "Timers subsystem"
62
63# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
64# only related to the tick functionality. Oneshot clockevent devices
65# are supported independ of this.
66config TICK_ONESHOT
67	bool
68
69config NO_HZ_COMMON
70	bool
71	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
72	select TICK_ONESHOT
73
74choice
75	prompt "Timer tick handling"
76	default NO_HZ_IDLE if NO_HZ
77
78config HZ_PERIODIC
79	bool "Periodic timer ticks (constant rate, no dynticks)"
80	help
81	  This option keeps the tick running periodically at a constant
82	  rate, even when the CPU doesn't need it.
83
84config NO_HZ_IDLE
85	bool "Idle dynticks system (tickless idle)"
86	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
87	select NO_HZ_COMMON
88	help
89	  This option enables a tickless idle system: timer interrupts
90	  will only trigger on an as-needed basis when the system is idle.
91	  This is usually interesting for energy saving.
92
93	  Most of the time you want to say Y here.
94
95config NO_HZ_FULL
96	bool "Full dynticks system (tickless)"
97	# NO_HZ_COMMON dependency
98	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
99	# We need at least one periodic CPU for timekeeping
100	depends on SMP
101	# RCU_USER_QS dependency
102	depends on HAVE_CONTEXT_TRACKING
103	# VIRT_CPU_ACCOUNTING_GEN dependency
104	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
105	select NO_HZ_COMMON
106	select RCU_USER_QS
107	select RCU_NOCB_CPU
108	select VIRT_CPU_ACCOUNTING_GEN
109	select IRQ_WORK
110	help
111	 Adaptively try to shutdown the tick whenever possible, even when
112	 the CPU is running tasks. Typically this requires running a single
113	 task on the CPU. Chances for running tickless are maximized when
114	 the task mostly runs in userspace and has few kernel activity.
115
116	 You need to fill up the nohz_full boot parameter with the
117	 desired range of dynticks CPUs.
118
119	 This is implemented at the expense of some overhead in user <-> kernel
120	 transitions: syscalls, exceptions and interrupts. Even when it's
121	 dynamically off.
122
123	 Say N.
124
125endchoice
126
127config NO_HZ_FULL_ALL
128       bool "Full dynticks system on all CPUs by default (except CPU 0)"
129       depends on NO_HZ_FULL
130       help
131         If the user doesn't pass the nohz_full boot option to
132	 define the range of full dynticks CPUs, consider that all
133	 CPUs in the system are full dynticks by default.
134	 Note the boot CPU will still be kept outside the range to
135	 handle the timekeeping duty.
136
137config NO_HZ_FULL_SYSIDLE
138	bool "Detect full-system idle state for full dynticks system"
139	depends on NO_HZ_FULL
140	default n
141	help
142	 At least one CPU must keep the scheduling-clock tick running for
143	 timekeeping purposes whenever there is a non-idle CPU, where
144	 "non-idle" also includes dynticks CPUs as long as they are
145	 running non-idle tasks.  Because the underlying adaptive-tick
146	 support cannot distinguish between all CPUs being idle and
147	 all CPUs each running a single task in dynticks mode, the
148	 underlying support simply ensures that there is always a CPU
149	 handling the scheduling-clock tick, whether or not all CPUs
150	 are idle.  This Kconfig option enables scalable detection of
151	 the all-CPUs-idle state, thus allowing the scheduling-clock
152	 tick to be disabled when all CPUs are idle.  Note that scalable
153	 detection of the all-CPUs-idle state means that larger systems
154	 will be slower to declare the all-CPUs-idle state.
155
156	 Say Y if you would like to help debug all-CPUs-idle detection.
157
158	 Say N if you are unsure.
159
160config NO_HZ_FULL_SYSIDLE_SMALL
161	int "Number of CPUs above which large-system approach is used"
162	depends on NO_HZ_FULL_SYSIDLE
163	range 1 NR_CPUS
164	default 8
165	help
166	 The full-system idle detection mechanism takes a lazy approach
167	 on large systems, as is required to attain decent scalability.
168	 However, on smaller systems, scalability is not anywhere near as
169	 large a concern as is energy efficiency.  The sysidle subsystem
170	 therefore uses a fast but non-scalable algorithm for small
171	 systems and a lazier but scalable algorithm for large systems.
172	 This Kconfig parameter defines the number of CPUs in the largest
173	 system that will be considered to be "small".
174
175	 The default value will be fine in most cases.	Battery-powered
176	 systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
177	 numbers of CPUs, and (3) are suffering from battery-lifetime
178	 problems due to long sysidle latencies might wish to experiment
179	 with larger values for this Kconfig parameter.  On the other
180	 hand, they might be even better served by disabling NO_HZ_FULL
181	 entirely, given that NO_HZ_FULL is intended for HPC and
182	 real-time workloads that at present do not tend to be run on
183	 battery-powered systems.
184
185	 Take the default if you are unsure.
186
187config NO_HZ
188	bool "Old Idle dynticks config"
189	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
190	help
191	  This is the old config entry that enables dynticks idle.
192	  We keep it around for a little while to enforce backward
193	  compatibility with older config files.
194
195config HIGH_RES_TIMERS
196	bool "High Resolution Timer Support"
197	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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
204endmenu
205endif
206