1# SPDX-License-Identifier: GPL-2.0-only 2# 3# Timer subsystem related configuration options 4# 5 6# Options selectable by arch Kconfig 7 8# Watchdog function for clocksources to detect instabilities 9config CLOCKSOURCE_WATCHDOG 10 bool 11 12# Architecture has extra clocksource data 13config ARCH_CLOCKSOURCE_DATA 14 bool 15 16# Architecture has extra clocksource init called from registration 17config ARCH_CLOCKSOURCE_INIT 18 bool 19 20config ARCH_WANTS_CLOCKSOURCE_READ_INLINE 21 bool 22 23# Timekeeping vsyscall support 24config GENERIC_TIME_VSYSCALL 25 bool 26 27# The generic clock events infrastructure 28config GENERIC_CLOCKEVENTS 29 def_bool !LEGACY_TIMER_TICK 30 31# Architecture can handle broadcast in a driver-agnostic way 32config ARCH_HAS_TICK_BROADCAST 33 bool 34 35# Clockevents broadcasting infrastructure 36config GENERIC_CLOCKEVENTS_BROADCAST 37 bool 38 depends on GENERIC_CLOCKEVENTS 39 40# Handle broadcast in default_idle_call() 41config GENERIC_CLOCKEVENTS_BROADCAST_IDLE 42 bool 43 depends on GENERIC_CLOCKEVENTS_BROADCAST 44 45# Automatically adjust the min. reprogramming time for 46# clock event device 47config GENERIC_CLOCKEVENTS_MIN_ADJUST 48 bool 49 50config GENERIC_CLOCKEVENTS_COUPLED 51 bool 52 53# Generic update of CMOS clock 54config GENERIC_CMOS_UPDATE 55 bool 56 57# Select to handle posix CPU timers from task_work 58# and not from the timer interrupt context 59config HAVE_POSIX_CPU_TIMERS_TASK_WORK 60 bool 61 62config POSIX_CPU_TIMERS_TASK_WORK 63 bool 64 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK 65 66config LEGACY_TIMER_TICK 67 bool 68 help 69 The legacy timer tick helper is used by platforms that 70 lack support for the generic clockevent framework. 71 New platforms should use generic clockevents instead. 72 73config TIME_KUNIT_TEST 74 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS 75 depends on KUNIT 76 default KUNIT_ALL_TESTS 77 help 78 Enable this option to test RTC library functions. 79 80 If unsure, say N. 81 82config CONTEXT_TRACKING 83 bool 84 85config CONTEXT_TRACKING_IDLE 86 bool 87 select CONTEXT_TRACKING 88 help 89 Tracks idle state on behalf of RCU. 90 91menu "Timers subsystem" 92 93if GENERIC_CLOCKEVENTS 94# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 95# only related to the tick functionality. Oneshot clockevent devices 96# are supported independent of this. 97config TICK_ONESHOT 98 bool 99 100config NO_HZ_COMMON 101 bool 102 select TICK_ONESHOT 103 104choice 105 prompt "Timer tick handling" 106 default NO_HZ_IDLE if NO_HZ 107 108config HZ_PERIODIC 109 bool "Periodic timer ticks (constant rate, no dynticks)" 110 help 111 This option keeps the tick running periodically at a constant 112 rate, even when the CPU doesn't need it. 113 114config NO_HZ_IDLE 115 bool "Idle dynticks system (tickless idle)" 116 select NO_HZ_COMMON 117 help 118 This option enables a tickless idle system: timer interrupts 119 will only trigger on an as-needed basis when the system is idle. 120 This is usually interesting for energy saving. 121 122 Most of the time you want to say Y here. 123 124config NO_HZ_FULL 125 bool "Full dynticks system (tickless)" 126 # NO_HZ_COMMON dependency 127 # We need at least one periodic CPU for timekeeping 128 depends on SMP 129 depends on HAVE_CONTEXT_TRACKING_USER 130 # VIRT_CPU_ACCOUNTING_GEN dependency 131 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 132 select NO_HZ_COMMON 133 select RCU_NOCB_CPU 134 select VIRT_CPU_ACCOUNTING_GEN 135 select IRQ_WORK 136 select CPU_ISOLATION 137 help 138 Adaptively try to shutdown the tick whenever possible, even when 139 the CPU is running tasks. Typically this requires running a single 140 task on the CPU. Chances for running tickless are maximized when 141 the task mostly runs in userspace and has few kernel activity. 142 143 You need to fill up the nohz_full boot parameter with the 144 desired range of dynticks CPUs to use it. This is implemented at 145 the expense of some overhead in user <-> kernel transitions: 146 syscalls, exceptions and interrupts. 147 148 By default, without passing the nohz_full parameter, this behaves just 149 like NO_HZ_IDLE. 150 151 If you're a distro say Y. 152 153endchoice 154 155config CONTEXT_TRACKING_USER 156 bool 157 depends on HAVE_CONTEXT_TRACKING_USER 158 select CONTEXT_TRACKING 159 help 160 Track transitions between kernel and user on behalf of RCU and 161 tickless cputime accounting. The former case relies on context 162 tracking to enter/exit RCU extended quiescent states. 163 164config CONTEXT_TRACKING_USER_FORCE 165 bool "Force user context tracking" 166 depends on CONTEXT_TRACKING_USER 167 default y if !NO_HZ_FULL 168 help 169 The major pre-requirement for full dynticks to work is to 170 support the user context tracking subsystem. But there are also 171 other dependencies to provide in order to make the full 172 dynticks working. 173 174 This option stands for testing when an arch implements the 175 user context tracking backend but doesn't yet fulfill all the 176 requirements to make the full dynticks feature working. 177 Without the full dynticks, there is no way to test the support 178 for user context tracking and the subsystems that rely on it: RCU 179 userspace extended quiescent state and tickless cputime 180 accounting. This option copes with the absence of the full 181 dynticks subsystem by forcing the user context tracking on all 182 CPUs in the system. 183 184 Say Y only if you're working on the development of an 185 architecture backend for the user context tracking. 186 187 Say N otherwise, this option brings an overhead that you 188 don't want in production. 189 190config NO_HZ 191 bool "Old Idle dynticks config" 192 help 193 This is the old config entry that enables dynticks idle. 194 We keep it around for a little while to enforce backward 195 compatibility with older config files. 196 197config HIGH_RES_TIMERS 198 bool "High Resolution Timer Support" 199 select TICK_ONESHOT 200 help 201 This option enables high resolution timer support. If your 202 hardware is not capable then this option only increases 203 the size of the kernel image. 204 205config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 206 int "Clocksource watchdog maximum allowable skew (in microseconds)" 207 depends on CLOCKSOURCE_WATCHDOG 208 range 50 1000 209 default 125 210 help 211 Specify the maximum amount of allowable watchdog skew in 212 microseconds before reporting the clocksource to be unstable. 213 The default is based on a half-second clocksource watchdog 214 interval and NTP's maximum frequency drift of 500 parts 215 per million. If the clocksource is good enough for NTP, 216 it is good enough for the clocksource watchdog! 217endif 218 219config POSIX_AUX_CLOCKS 220 bool "Enable auxiliary POSIX clocks" 221 depends on POSIX_TIMERS 222 help 223 Auxiliary POSIX clocks are clocks which can be steered 224 independently of the core timekeeper, which controls the 225 MONOTONIC, REALTIME, BOOTTIME and TAI clocks. They are useful to 226 provide e.g. lockless time accessors to independent PTP clocks 227 and other clock domains, which are not correlated to the TAI/NTP 228 notion of time. 229 230endmenu 231