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 53config GENERIC_CLOCKEVENTS_COUPLED_INLINE 54 select GENERIC_CLOCKEVENTS_COUPLED 55 bool 56 57# Generic update of CMOS clock 58config GENERIC_CMOS_UPDATE 59 bool 60 61# Select to handle posix CPU timers from task_work 62# and not from the timer interrupt context 63config HAVE_POSIX_CPU_TIMERS_TASK_WORK 64 bool 65 66config POSIX_CPU_TIMERS_TASK_WORK 67 bool 68 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK 69 70config LEGACY_TIMER_TICK 71 bool 72 help 73 The legacy timer tick helper is used by platforms that 74 lack support for the generic clockevent framework. 75 New platforms should use generic clockevents instead. 76 77config TIME_KUNIT_TEST 78 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS 79 depends on KUNIT 80 default KUNIT_ALL_TESTS 81 help 82 Enable this option to test RTC library functions. 83 84 If unsure, say N. 85 86config CONTEXT_TRACKING 87 bool 88 89config CONTEXT_TRACKING_IDLE 90 bool 91 select CONTEXT_TRACKING 92 help 93 Tracks idle state on behalf of RCU. 94 95menu "Timers subsystem" 96 97if GENERIC_CLOCKEVENTS 98# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 99# only related to the tick functionality. Oneshot clockevent devices 100# are supported independent of this. 101config TICK_ONESHOT 102 bool 103 104config NO_HZ_COMMON 105 bool 106 select TICK_ONESHOT 107 108choice 109 prompt "Timer tick handling" 110 default NO_HZ_IDLE if NO_HZ 111 112config HZ_PERIODIC 113 bool "Periodic timer ticks (constant rate, no dynticks)" 114 help 115 This option keeps the tick running periodically at a constant 116 rate, even when the CPU doesn't need it. 117 118config NO_HZ_IDLE 119 bool "Idle dynticks system (tickless idle)" 120 select NO_HZ_COMMON 121 help 122 This option enables a tickless idle system: timer interrupts 123 will only trigger on an as-needed basis when the system is idle. 124 This is usually interesting for energy saving. 125 126 Most of the time you want to say Y here. 127 128config NO_HZ_FULL 129 bool "Full dynticks system (tickless)" 130 # NO_HZ_COMMON dependency 131 # We need at least one periodic CPU for timekeeping 132 depends on SMP 133 depends on HAVE_CONTEXT_TRACKING_USER 134 # VIRT_CPU_ACCOUNTING_GEN dependency 135 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 136 select NO_HZ_COMMON 137 select RCU_NOCB_CPU 138 select VIRT_CPU_ACCOUNTING_GEN 139 select IRQ_WORK 140 select CPU_ISOLATION 141 help 142 Adaptively try to shutdown the tick whenever possible, even when 143 the CPU is running tasks. Typically this requires running a single 144 task on the CPU. Chances for running tickless are maximized when 145 the task mostly runs in userspace and has few kernel activity. 146 147 You need to fill up the nohz_full boot parameter with the 148 desired range of dynticks CPUs to use it. This is implemented at 149 the expense of some overhead in user <-> kernel transitions: 150 syscalls, exceptions and interrupts. 151 152 By default, without passing the nohz_full parameter, this behaves just 153 like NO_HZ_IDLE. 154 155 If you're a distro say Y. 156 157endchoice 158 159config CONTEXT_TRACKING_USER 160 bool 161 depends on HAVE_CONTEXT_TRACKING_USER 162 select CONTEXT_TRACKING 163 help 164 Track transitions between kernel and user on behalf of RCU and 165 tickless cputime accounting. The former case relies on context 166 tracking to enter/exit RCU extended quiescent states. 167 168config CONTEXT_TRACKING_USER_FORCE 169 bool "Force user context tracking" 170 depends on CONTEXT_TRACKING_USER 171 default y if !NO_HZ_FULL 172 help 173 The major pre-requirement for full dynticks to work is to 174 support the user context tracking subsystem. But there are also 175 other dependencies to provide in order to make the full 176 dynticks working. 177 178 This option stands for testing when an arch implements the 179 user context tracking backend but doesn't yet fulfill all the 180 requirements to make the full dynticks feature working. 181 Without the full dynticks, there is no way to test the support 182 for user context tracking and the subsystems that rely on it: RCU 183 userspace extended quiescent state and tickless cputime 184 accounting. This option copes with the absence of the full 185 dynticks subsystem by forcing the user context tracking on all 186 CPUs in the system. 187 188 Say Y only if you're working on the development of an 189 architecture backend for the user context tracking. 190 191 Say N otherwise, this option brings an overhead that you 192 don't want in production. 193 194config NO_HZ 195 bool "Old Idle dynticks config" 196 help 197 This is the old config entry that enables dynticks idle. 198 We keep it around for a little while to enforce backward 199 compatibility with older config files. 200 201config HIGH_RES_TIMERS 202 bool "High Resolution Timer Support" 203 select TICK_ONESHOT 204 help 205 This option enables high resolution timer support. If your 206 hardware is not capable then this option only increases 207 the size of the kernel image. 208 209config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 210 int "Clocksource watchdog maximum allowable skew (in microseconds)" 211 depends on CLOCKSOURCE_WATCHDOG 212 range 50 1000 213 default 125 214 help 215 Specify the maximum amount of allowable watchdog skew in 216 microseconds before reporting the clocksource to be unstable. 217 The default is based on a half-second clocksource watchdog 218 interval and NTP's maximum frequency drift of 500 parts 219 per million. If the clocksource is good enough for NTP, 220 it is good enough for the clocksource watchdog! 221endif 222 223config POSIX_AUX_CLOCKS 224 bool "Enable auxiliary POSIX clocks" 225 depends on POSIX_TIMERS 226 help 227 Auxiliary POSIX clocks are clocks which can be steered 228 independently of the core timekeeper, which controls the 229 MONOTONIC, REALTIME, BOOTTIME and TAI clocks. They are useful to 230 provide e.g. lockless time accessors to independent PTP clocks 231 and other clock domains, which are not correlated to the TAI/NTP 232 notion of time. 233 234endmenu 235