2 # Timer subsystem related configuration options
5 # Options selectable by arch Kconfig
7 # Watchdog function for clocksources to detect instabilities
8 config CLOCKSOURCE_WATCHDOG
11 # Architecture has extra clocksource data
12 config ARCH_CLOCKSOURCE_DATA
15 # Timekeeping vsyscall support
16 config GENERIC_TIME_VSYSCALL
19 # Timekeeping vsyscall support
20 config GENERIC_TIME_VSYSCALL_OLD
23 # Old style timekeeping
24 config ARCH_USES_GETTIMEOFFSET
27 # The generic clock events infrastructure
28 config GENERIC_CLOCKEVENTS
31 # Migration helper. Builds, but does not invoke
32 config GENERIC_CLOCKEVENTS_BUILD
35 depends on GENERIC_CLOCKEVENTS
37 # Architecture can handle broadcast in a driver-agnostic way
38 config ARCH_HAS_TICK_BROADCAST
41 # Clockevents broadcasting infrastructure
42 config GENERIC_CLOCKEVENTS_BROADCAST
44 depends on GENERIC_CLOCKEVENTS
46 # Automatically adjust the min. reprogramming time for
48 config GENERIC_CLOCKEVENTS_MIN_ADJUST
51 # Generic update of CMOS clock
52 config GENERIC_CMOS_UPDATE
55 if GENERIC_CLOCKEVENTS
56 menu "Timers subsystem"
58 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
59 # only related to the tick functionality. Oneshot clockevent devices
60 # are supported independ of this.
66 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
70 prompt "Timer tick handling"
71 default NO_HZ_IDLE if NO_HZ
74 bool "Periodic timer ticks (constant rate, no dynticks)"
76 This option keeps the tick running periodically at a constant
77 rate, even when the CPU doesn't need it.
80 bool "Idle dynticks system (tickless idle)"
81 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
84 This option enables a tickless idle system: timer interrupts
85 will only trigger on an as-needed basis when the system is idle.
86 This is usually interesting for energy saving.
88 Most of the time you want to say Y here.
91 bool "Full dynticks system (tickless)"
92 # NO_HZ_COMMON dependency
93 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
94 # We need at least one periodic CPU for timekeeping
96 # RCU_USER_QS dependency
97 depends on HAVE_CONTEXT_TRACKING
98 # VIRT_CPU_ACCOUNTING_GEN dependency
99 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
103 select VIRT_CPU_ACCOUNTING_GEN
106 Adaptively try to shutdown the tick whenever possible, even when
107 the CPU is running tasks. Typically this requires running a single
108 task on the CPU. Chances for running tickless are maximized when
109 the task mostly runs in userspace and has few kernel activity.
111 You need to fill up the nohz_full boot parameter with the
112 desired range of dynticks CPUs.
114 This is implemented at the expense of some overhead in user <-> kernel
115 transitions: syscalls, exceptions and interrupts. Even when it's
122 config NO_HZ_FULL_ALL
123 bool "Full dynticks system on all CPUs by default (except CPU 0)"
124 depends on NO_HZ_FULL
126 If the user doesn't pass the nohz_full boot option to
127 define the range of full dynticks CPUs, consider that all
128 CPUs in the system are full dynticks by default.
129 Note the boot CPU will still be kept outside the range to
130 handle the timekeeping duty.
132 config NO_HZ_FULL_SYSIDLE
133 bool "Detect full-system idle state for full dynticks system"
134 depends on NO_HZ_FULL
137 At least one CPU must keep the scheduling-clock tick running for
138 timekeeping purposes whenever there is a non-idle CPU, where
139 "non-idle" also includes dynticks CPUs as long as they are
140 running non-idle tasks. Because the underlying adaptive-tick
141 support cannot distinguish between all CPUs being idle and
142 all CPUs each running a single task in dynticks mode, the
143 underlying support simply ensures that there is always a CPU
144 handling the scheduling-clock tick, whether or not all CPUs
145 are idle. This Kconfig option enables scalable detection of
146 the all-CPUs-idle state, thus allowing the scheduling-clock
147 tick to be disabled when all CPUs are idle. Note that scalable
148 detection of the all-CPUs-idle state means that larger systems
149 will be slower to declare the all-CPUs-idle state.
151 Say Y if you would like to help debug all-CPUs-idle detection.
153 Say N if you are unsure.
155 config NO_HZ_FULL_SYSIDLE_SMALL
156 int "Number of CPUs above which large-system approach is used"
157 depends on NO_HZ_FULL_SYSIDLE
161 The full-system idle detection mechanism takes a lazy approach
162 on large systems, as is required to attain decent scalability.
163 However, on smaller systems, scalability is not anywhere near as
164 large a concern as is energy efficiency. The sysidle subsystem
165 therefore uses a fast but non-scalable algorithm for small
166 systems and a lazier but scalable algorithm for large systems.
167 This Kconfig parameter defines the number of CPUs in the largest
168 system that will be considered to be "small".
170 The default value will be fine in most cases. Battery-powered
171 systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
172 numbers of CPUs, and (3) are suffering from battery-lifetime
173 problems due to long sysidle latencies might wish to experiment
174 with larger values for this Kconfig parameter. On the other
175 hand, they might be even better served by disabling NO_HZ_FULL
176 entirely, given that NO_HZ_FULL is intended for HPC and
177 real-time workloads that at present do not tend to be run on
178 battery-powered systems.
180 Take the default if you are unsure.
183 bool "Old Idle dynticks config"
184 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
186 This is the old config entry that enables dynticks idle.
187 We keep it around for a little while to enforce backward
188 compatibility with older config files.
190 config HIGH_RES_TIMERS
191 bool "High Resolution Timer Support"
192 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
195 This option enables high resolution timer support. If your
196 hardware is not capable then this option only increases
197 the size of the kernel image.