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 20# Clocksources require validation of the clocksource against the last 21# cycle update - x86/TSC misfeature 22config CLOCKSOURCE_VALIDATE_LAST_CYCLE 23 bool 24 25# Timekeeping vsyscall support 26config GENERIC_TIME_VSYSCALL 27 bool 28 29# The generic clock events infrastructure 30config GENERIC_CLOCKEVENTS 31 def_bool !LEGACY_TIMER_TICK 32 33# Architecture can handle broadcast in a driver-agnostic way 34config ARCH_HAS_TICK_BROADCAST 35 bool 36 37# Clockevents broadcasting infrastructure 38config GENERIC_CLOCKEVENTS_BROADCAST 39 bool 40 depends on GENERIC_CLOCKEVENTS 41 42# Handle broadcast in default_idle_call() 43config GENERIC_CLOCKEVENTS_BROADCAST_IDLE 44 bool 45 depends on GENERIC_CLOCKEVENTS_BROADCAST 46 47# Automatically adjust the min. reprogramming time for 48# clock event device 49config GENERIC_CLOCKEVENTS_MIN_ADJUST 50 bool 51 52# Generic update of CMOS clock 53config GENERIC_CMOS_UPDATE 54 bool 55 56# Select to handle posix CPU timers from task_work 57# and not from the timer interrupt context 58config HAVE_POSIX_CPU_TIMERS_TASK_WORK 59 bool 60 61config POSIX_CPU_TIMERS_TASK_WORK 62 bool 63 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK 64 65config LEGACY_TIMER_TICK 66 bool 67 help 68 The legacy timer tick helper is used by platforms that 69 lack support for the generic clockevent framework. 70 New platforms should use generic clockevents instead. 71 72config TIME_KUNIT_TEST 73 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS 74 depends on KUNIT 75 default KUNIT_ALL_TESTS 76 help 77 Enable this option to test RTC library functions. 78 79 If unsure, say N. 80 81config CONTEXT_TRACKING 82 bool 83 84config CONTEXT_TRACKING_IDLE 85 bool 86 select CONTEXT_TRACKING 87 help 88 Tracks idle state on behalf of RCU. 89 90if GENERIC_CLOCKEVENTS 91menu "Timers subsystem" 92 93# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 94# only related to the tick functionality. Oneshot clockevent devices 95# are supported independent of this. 96config TICK_ONESHOT 97 bool 98 99config NO_HZ_COMMON 100 bool 101 select TICK_ONESHOT 102 103choice 104 prompt "Timer tick handling" 105 default NO_HZ_IDLE if NO_HZ 106 107config HZ_PERIODIC 108 bool "Periodic timer ticks (constant rate, no dynticks)" 109 help 110 This option keeps the tick running periodically at a constant 111 rate, even when the CPU doesn't need it. 112 113config NO_HZ_IDLE 114 bool "Idle dynticks system (tickless idle)" 115 select NO_HZ_COMMON 116 help 117 This option enables a tickless idle system: timer interrupts 118 will only trigger on an as-needed basis when the system is idle. 119 This is usually interesting for energy saving. 120 121 Most of the time you want to say Y here. 122 123config NO_HZ_FULL 124 bool "Full dynticks system (tickless)" 125 # NO_HZ_COMMON dependency 126 # We need at least one periodic CPU for timekeeping 127 depends on SMP 128 depends on HAVE_CONTEXT_TRACKING_USER 129 # VIRT_CPU_ACCOUNTING_GEN dependency 130 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 131 select NO_HZ_COMMON 132 select RCU_NOCB_CPU 133 select VIRT_CPU_ACCOUNTING_GEN 134 select IRQ_WORK 135 select CPU_ISOLATION 136 help 137 Adaptively try to shutdown the tick whenever possible, even when 138 the CPU is running tasks. Typically this requires running a single 139 task on the CPU. Chances for running tickless are maximized when 140 the task mostly runs in userspace and has few kernel activity. 141 142 You need to fill up the nohz_full boot parameter with the 143 desired range of dynticks CPUs to use it. This is implemented at 144 the expense of some overhead in user <-> kernel transitions: 145 syscalls, exceptions and interrupts. 146 147 By default, without passing the nohz_full parameter, this behaves just 148 like NO_HZ_IDLE. 149 150 If you're a distro say Y. 151 152endchoice 153 154config CONTEXT_TRACKING_USER 155 bool 156 depends on HAVE_CONTEXT_TRACKING_USER 157 select CONTEXT_TRACKING 158 help 159 Track transitions between kernel and user on behalf of RCU and 160 tickless cputime accounting. The former case relies on context 161 tracking to enter/exit RCU extended quiescent states. 162 163config CONTEXT_TRACKING_USER_FORCE 164 bool "Force user context tracking" 165 depends on CONTEXT_TRACKING_USER 166 default y if !NO_HZ_FULL 167 help 168 The major pre-requirement for full dynticks to work is to 169 support the user context tracking subsystem. But there are also 170 other dependencies to provide in order to make the full 171 dynticks working. 172 173 This option stands for testing when an arch implements the 174 user context tracking backend but doesn't yet fulfill all the 175 requirements to make the full dynticks feature working. 176 Without the full dynticks, there is no way to test the support 177 for user context tracking and the subsystems that rely on it: RCU 178 userspace extended quiescent state and tickless cputime 179 accounting. This option copes with the absence of the full 180 dynticks subsystem by forcing the user context tracking on all 181 CPUs in the system. 182 183 Say Y only if you're working on the development of an 184 architecture backend for the user context tracking. 185 186 Say N otherwise, this option brings an overhead that you 187 don't want in production. 188 189config NO_HZ 190 bool "Old Idle dynticks config" 191 help 192 This is the old config entry that enables dynticks idle. 193 We keep it around for a little while to enforce backward 194 compatibility with older config files. 195 196config HIGH_RES_TIMERS 197 bool "High Resolution Timer Support" 198 select TICK_ONESHOT 199 help 200 This option enables high resolution timer support. If your 201 hardware is not capable then this option only increases 202 the size of the kernel image. 203 204config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 205 int "Clocksource watchdog maximum allowable skew (in μs)" 206 depends on CLOCKSOURCE_WATCHDOG 207 range 50 1000 208 default 125 209 help 210 Specify the maximum amount of allowable watchdog skew in 211 microseconds before reporting the clocksource to be unstable. 212 The default is based on a half-second clocksource watchdog 213 interval and NTP's maximum frequency drift of 500 parts 214 per million. If the clocksource is good enough for NTP, 215 it is good enough for the clocksource watchdog! 216 217endmenu 218endif 219