0001 # SPDX-License-Identifier: GPL-2.0-only
0002 #
0003 # Timer subsystem related configuration options
0004 #
0005
0006 # Options selectable by arch Kconfig
0007
0008 # Watchdog function for clocksources to detect instabilities
0009 config CLOCKSOURCE_WATCHDOG
0010 bool
0011
0012 # Architecture has extra clocksource data
0013 config ARCH_CLOCKSOURCE_DATA
0014 bool
0015
0016 # Architecture has extra clocksource init called from registration
0017 config ARCH_CLOCKSOURCE_INIT
0018 bool
0019
0020 # Clocksources require validation of the clocksource against the last
0021 # cycle update - x86/TSC misfeature
0022 config CLOCKSOURCE_VALIDATE_LAST_CYCLE
0023 bool
0024
0025 # Timekeeping vsyscall support
0026 config GENERIC_TIME_VSYSCALL
0027 bool
0028
0029 # The generic clock events infrastructure
0030 config GENERIC_CLOCKEVENTS
0031 def_bool !LEGACY_TIMER_TICK
0032
0033 # Architecture can handle broadcast in a driver-agnostic way
0034 config ARCH_HAS_TICK_BROADCAST
0035 bool
0036
0037 # Clockevents broadcasting infrastructure
0038 config GENERIC_CLOCKEVENTS_BROADCAST
0039 bool
0040 depends on GENERIC_CLOCKEVENTS
0041
0042 # Automatically adjust the min. reprogramming time for
0043 # clock event device
0044 config GENERIC_CLOCKEVENTS_MIN_ADJUST
0045 bool
0046
0047 # Generic update of CMOS clock
0048 config GENERIC_CMOS_UPDATE
0049 bool
0050
0051 # Select to handle posix CPU timers from task_work
0052 # and not from the timer interrupt context
0053 config HAVE_POSIX_CPU_TIMERS_TASK_WORK
0054 bool
0055
0056 config POSIX_CPU_TIMERS_TASK_WORK
0057 bool
0058 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
0059
0060 config LEGACY_TIMER_TICK
0061 bool
0062 help
0063 The legacy timer tick helper is used by platforms that
0064 lack support for the generic clockevent framework.
0065 New platforms should use generic clockevents instead.
0066
0067 config TIME_KUNIT_TEST
0068 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
0069 depends on KUNIT
0070 default KUNIT_ALL_TESTS
0071 help
0072 Enable this option to test RTC library functions.
0073
0074 If unsure, say N.
0075
0076 config CONTEXT_TRACKING
0077 bool
0078
0079 config CONTEXT_TRACKING_IDLE
0080 bool
0081 select CONTEXT_TRACKING
0082 help
0083 Tracks idle state on behalf of RCU.
0084
0085 if GENERIC_CLOCKEVENTS
0086 menu "Timers subsystem"
0087
0088 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
0089 # only related to the tick functionality. Oneshot clockevent devices
0090 # are supported independent of this.
0091 config TICK_ONESHOT
0092 bool
0093
0094 config NO_HZ_COMMON
0095 bool
0096 select TICK_ONESHOT
0097
0098 choice
0099 prompt "Timer tick handling"
0100 default NO_HZ_IDLE if NO_HZ
0101
0102 config HZ_PERIODIC
0103 bool "Periodic timer ticks (constant rate, no dynticks)"
0104 help
0105 This option keeps the tick running periodically at a constant
0106 rate, even when the CPU doesn't need it.
0107
0108 config NO_HZ_IDLE
0109 bool "Idle dynticks system (tickless idle)"
0110 select NO_HZ_COMMON
0111 help
0112 This option enables a tickless idle system: timer interrupts
0113 will only trigger on an as-needed basis when the system is idle.
0114 This is usually interesting for energy saving.
0115
0116 Most of the time you want to say Y here.
0117
0118 config NO_HZ_FULL
0119 bool "Full dynticks system (tickless)"
0120 # NO_HZ_COMMON dependency
0121 # We need at least one periodic CPU for timekeeping
0122 depends on SMP
0123 depends on HAVE_CONTEXT_TRACKING_USER
0124 # VIRT_CPU_ACCOUNTING_GEN dependency
0125 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
0126 select NO_HZ_COMMON
0127 select RCU_NOCB_CPU
0128 select VIRT_CPU_ACCOUNTING_GEN
0129 select IRQ_WORK
0130 select CPU_ISOLATION
0131 help
0132 Adaptively try to shutdown the tick whenever possible, even when
0133 the CPU is running tasks. Typically this requires running a single
0134 task on the CPU. Chances for running tickless are maximized when
0135 the task mostly runs in userspace and has few kernel activity.
0136
0137 You need to fill up the nohz_full boot parameter with the
0138 desired range of dynticks CPUs to use it. This is implemented at
0139 the expense of some overhead in user <-> kernel transitions:
0140 syscalls, exceptions and interrupts.
0141
0142 By default, without passing the nohz_full parameter, this behaves just
0143 like NO_HZ_IDLE.
0144
0145 If you're a distro say Y.
0146
0147 endchoice
0148
0149 config CONTEXT_TRACKING_USER
0150 bool
0151 depends on HAVE_CONTEXT_TRACKING_USER
0152 select CONTEXT_TRACKING
0153 help
0154 Track transitions between kernel and user on behalf of RCU and
0155 tickless cputime accounting. The former case relies on context
0156 tracking to enter/exit RCU extended quiescent states.
0157
0158 config CONTEXT_TRACKING_USER_FORCE
0159 bool "Force user context tracking"
0160 depends on CONTEXT_TRACKING_USER
0161 default y if !NO_HZ_FULL
0162 help
0163 The major pre-requirement for full dynticks to work is to
0164 support the user context tracking subsystem. But there are also
0165 other dependencies to provide in order to make the full
0166 dynticks working.
0167
0168 This option stands for testing when an arch implements the
0169 user context tracking backend but doesn't yet fulfill all the
0170 requirements to make the full dynticks feature working.
0171 Without the full dynticks, there is no way to test the support
0172 for user context tracking and the subsystems that rely on it: RCU
0173 userspace extended quiescent state and tickless cputime
0174 accounting. This option copes with the absence of the full
0175 dynticks subsystem by forcing the user context tracking on all
0176 CPUs in the system.
0177
0178 Say Y only if you're working on the development of an
0179 architecture backend for the user context tracking.
0180
0181 Say N otherwise, this option brings an overhead that you
0182 don't want in production.
0183
0184 config NO_HZ
0185 bool "Old Idle dynticks config"
0186 help
0187 This is the old config entry that enables dynticks idle.
0188 We keep it around for a little while to enforce backward
0189 compatibility with older config files.
0190
0191 config HIGH_RES_TIMERS
0192 bool "High Resolution Timer Support"
0193 select TICK_ONESHOT
0194 help
0195 This option enables high resolution timer support. If your
0196 hardware is not capable then this option only increases
0197 the size of the kernel image.
0198
0199 config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
0200 int "Clocksource watchdog maximum allowable skew (in μs)"
0201 depends on CLOCKSOURCE_WATCHDOG
0202 range 50 1000
0203 default 100
0204 help
0205 Specify the maximum amount of allowable watchdog skew in
0206 microseconds before reporting the clocksource to be unstable.
0207
0208 endmenu
0209 endif
