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 76if GENERIC_CLOCKEVENTS 77menu "Timers subsystem" 78 79# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 80# only related to the tick functionality. Oneshot clockevent devices 81# are supported independent of this. 82config TICK_ONESHOT 83 bool 84 85config NO_HZ_COMMON 86 bool 87 select TICK_ONESHOT 88 89choice 90 prompt "Timer tick handling" 91 default NO_HZ_IDLE if NO_HZ 92 93config HZ_PERIODIC 94 bool "Periodic timer ticks (constant rate, no dynticks)" 95 help 96 This option keeps the tick running periodically at a constant 97 rate, even when the CPU doesn't need it. 98 99config NO_HZ_IDLE 100 bool "Idle dynticks system (tickless idle)" 101 select NO_HZ_COMMON 102 help 103 This option enables a tickless idle system: timer interrupts 104 will only trigger on an as-needed basis when the system is idle. 105 This is usually interesting for energy saving. 106 107 Most of the time you want to say Y here. 108 109config NO_HZ_FULL 110 bool "Full dynticks system (tickless)" 111 # NO_HZ_COMMON dependency 112 # We need at least one periodic CPU for timekeeping 113 depends on SMP 114 depends on HAVE_CONTEXT_TRACKING 115 # VIRT_CPU_ACCOUNTING_GEN dependency 116 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 117 select NO_HZ_COMMON 118 select RCU_NOCB_CPU 119 select VIRT_CPU_ACCOUNTING_GEN 120 select IRQ_WORK 121 select CPU_ISOLATION 122 help 123 Adaptively try to shutdown the tick whenever possible, even when 124 the CPU is running tasks. Typically this requires running a single 125 task on the CPU. Chances for running tickless are maximized when 126 the task mostly runs in userspace and has few kernel activity. 127 128 You need to fill up the nohz_full boot parameter with the 129 desired range of dynticks CPUs to use it. This is implemented at 130 the expense of some overhead in user <-> kernel transitions: 131 syscalls, exceptions and interrupts. 132 133 By default, without passing the nohz_full parameter, this behaves just 134 like NO_HZ_IDLE. 135 136 If you're a distro say Y. 137 138endchoice 139 140config CONTEXT_TRACKING 141 bool 142 143config CONTEXT_TRACKING_FORCE 144 bool "Force context tracking" 145 depends on CONTEXT_TRACKING 146 default y if !NO_HZ_FULL 147 help 148 The major pre-requirement for full dynticks to work is to 149 support the context tracking subsystem. But there are also 150 other dependencies to provide in order to make the full 151 dynticks working. 152 153 This option stands for testing when an arch implements the 154 context tracking backend but doesn't yet fulfill all the 155 requirements to make the full dynticks feature working. 156 Without the full dynticks, there is no way to test the support 157 for context tracking and the subsystems that rely on it: RCU 158 userspace extended quiescent state and tickless cputime 159 accounting. This option copes with the absence of the full 160 dynticks subsystem by forcing the context tracking on all 161 CPUs in the system. 162 163 Say Y only if you're working on the development of an 164 architecture backend for the context tracking. 165 166 Say N otherwise, this option brings an overhead that you 167 don't want in production. 168 169config NO_HZ 170 bool "Old Idle dynticks config" 171 help 172 This is the old config entry that enables dynticks idle. 173 We keep it around for a little while to enforce backward 174 compatibility with older config files. 175 176config HIGH_RES_TIMERS 177 bool "High Resolution Timer Support" 178 select TICK_ONESHOT 179 help 180 This option enables high resolution timer support. If your 181 hardware is not capable then this option only increases 182 the size of the kernel image. 183 184endmenu 185endif 186