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