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# Deferred rearming of the hrtimer interrupt 62config HRTIMER_REARM_DEFERRED 63 def_bool n 64 65# Select to handle posix CPU timers from task_work 66# and not from the timer interrupt context 67config HAVE_POSIX_CPU_TIMERS_TASK_WORK 68 bool 69 70config POSIX_CPU_TIMERS_TASK_WORK 71 bool 72 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK 73 74config LEGACY_TIMER_TICK 75 bool 76 help 77 The legacy timer tick helper is used by platforms that 78 lack support for the generic clockevent framework. 79 New platforms should use generic clockevents instead. 80 81config TIME_KUNIT_TEST 82 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS 83 depends on KUNIT 84 default KUNIT_ALL_TESTS 85 help 86 Enable this option to test RTC library functions. 87 88 If unsure, say N. 89 90config CONTEXT_TRACKING 91 bool 92 93config CONTEXT_TRACKING_IDLE 94 bool 95 select CONTEXT_TRACKING 96 help 97 Tracks idle state on behalf of RCU. 98 99menu "Timers subsystem" 100 101if GENERIC_CLOCKEVENTS 102# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 103# only related to the tick functionality. Oneshot clockevent devices 104# are supported independent of this. 105config TICK_ONESHOT 106 bool 107 108config NO_HZ_COMMON 109 bool 110 select TICK_ONESHOT 111 112choice 113 prompt "Timer tick handling" 114 default NO_HZ_IDLE if NO_HZ 115 116config HZ_PERIODIC 117 bool "Periodic timer ticks (constant rate, no dynticks)" 118 help 119 This option keeps the tick running periodically at a constant 120 rate, even when the CPU doesn't need it. 121 122config NO_HZ_IDLE 123 bool "Idle dynticks system (tickless idle)" 124 select NO_HZ_COMMON 125 help 126 This option enables a tickless idle system: timer interrupts 127 will only trigger on an as-needed basis when the system is idle. 128 This is usually interesting for energy saving. 129 130 Most of the time you want to say Y here. 131 132config NO_HZ_FULL 133 bool "Full dynticks system (tickless)" 134 # NO_HZ_COMMON dependency 135 # We need at least one periodic CPU for timekeeping 136 depends on SMP 137 depends on HAVE_CONTEXT_TRACKING_USER 138 # VIRT_CPU_ACCOUNTING_GEN dependency 139 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 140 select NO_HZ_COMMON 141 select RCU_NOCB_CPU 142 select VIRT_CPU_ACCOUNTING_GEN 143 select IRQ_WORK 144 select CPU_ISOLATION 145 help 146 Adaptively try to shutdown the tick whenever possible, even when 147 the CPU is running tasks. Typically this requires running a single 148 task on the CPU. Chances for running tickless are maximized when 149 the task mostly runs in userspace and has few kernel activity. 150 151 You need to fill up the nohz_full boot parameter with the 152 desired range of dynticks CPUs to use it. This is implemented at 153 the expense of some overhead in user <-> kernel transitions: 154 syscalls, exceptions and interrupts. 155 156 By default, without passing the nohz_full parameter, this behaves just 157 like NO_HZ_IDLE. 158 159 If you're a distro say Y. 160 161endchoice 162 163config CONTEXT_TRACKING_USER 164 bool 165 depends on HAVE_CONTEXT_TRACKING_USER 166 select CONTEXT_TRACKING 167 help 168 Track transitions between kernel and user on behalf of RCU and 169 tickless cputime accounting. The former case relies on context 170 tracking to enter/exit RCU extended quiescent states. 171 172config CONTEXT_TRACKING_USER_FORCE 173 bool "Force user context tracking" 174 depends on CONTEXT_TRACKING_USER 175 default y if !NO_HZ_FULL 176 help 177 The major pre-requirement for full dynticks to work is to 178 support the user context tracking subsystem. But there are also 179 other dependencies to provide in order to make the full 180 dynticks working. 181 182 This option stands for testing when an arch implements the 183 user context tracking backend but doesn't yet fulfill all the 184 requirements to make the full dynticks feature working. 185 Without the full dynticks, there is no way to test the support 186 for user context tracking and the subsystems that rely on it: RCU 187 userspace extended quiescent state and tickless cputime 188 accounting. This option copes with the absence of the full 189 dynticks subsystem by forcing the user context tracking on all 190 CPUs in the system. 191 192 Say Y only if you're working on the development of an 193 architecture backend for the user context tracking. 194 195 Say N otherwise, this option brings an overhead that you 196 don't want in production. 197 198config NO_HZ 199 bool "Old Idle dynticks config" 200 help 201 This is the old config entry that enables dynticks idle. 202 We keep it around for a little while to enforce backward 203 compatibility with older config files. 204 205config HIGH_RES_TIMERS 206 bool "High Resolution Timer Support" 207 select TICK_ONESHOT 208 help 209 This option enables high resolution timer support. If your 210 hardware is not capable then this option only increases 211 the size of the kernel image. 212 213config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 214 int "Clocksource watchdog maximum allowable skew (in microseconds)" 215 depends on CLOCKSOURCE_WATCHDOG 216 range 50 1000 217 default 125 218 help 219 Specify the maximum amount of allowable watchdog skew in 220 microseconds before reporting the clocksource to be unstable. 221 The default is based on a half-second clocksource watchdog 222 interval and NTP's maximum frequency drift of 500 parts 223 per million. If the clocksource is good enough for NTP, 224 it is good enough for the clocksource watchdog! 225endif 226 227config POSIX_AUX_CLOCKS 228 bool "Enable auxiliary POSIX clocks" 229 depends on POSIX_TIMERS 230 help 231 Auxiliary POSIX clocks are clocks which can be steered 232 independently of the core timekeeper, which controls the 233 MONOTONIC, REALTIME, BOOTTIME and TAI clocks. They are useful to 234 provide e.g. lockless time accessors to independent PTP clocks 235 and other clock domains, which are not correlated to the TAI/NTP 236 notion of time. 237 238endmenu 239