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