xref: /openbmc/linux/kernel/time/Kconfig (revision e23feb16)
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 64BIT
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"
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
205