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