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 67if GENERIC_CLOCKEVENTS 68menu "Timers subsystem" 69 70# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 71# only related to the tick functionality. Oneshot clockevent devices 72# are supported independent of this. 73config TICK_ONESHOT 74 bool 75 76config NO_HZ_COMMON 77 bool 78 select TICK_ONESHOT 79 80choice 81 prompt "Timer tick handling" 82 default NO_HZ_IDLE if NO_HZ 83 84config HZ_PERIODIC 85 bool "Periodic timer ticks (constant rate, no dynticks)" 86 help 87 This option keeps the tick running periodically at a constant 88 rate, even when the CPU doesn't need it. 89 90config NO_HZ_IDLE 91 bool "Idle dynticks system (tickless idle)" 92 select NO_HZ_COMMON 93 help 94 This option enables a tickless idle system: timer interrupts 95 will only trigger on an as-needed basis when the system is idle. 96 This is usually interesting for energy saving. 97 98 Most of the time you want to say Y here. 99 100config NO_HZ_FULL 101 bool "Full dynticks system (tickless)" 102 # NO_HZ_COMMON dependency 103 # We need at least one periodic CPU for timekeeping 104 depends on SMP 105 depends on HAVE_CONTEXT_TRACKING 106 # VIRT_CPU_ACCOUNTING_GEN dependency 107 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 108 select NO_HZ_COMMON 109 select RCU_NOCB_CPU 110 select VIRT_CPU_ACCOUNTING_GEN 111 select IRQ_WORK 112 select CPU_ISOLATION 113 help 114 Adaptively try to shutdown the tick whenever possible, even when 115 the CPU is running tasks. Typically this requires running a single 116 task on the CPU. Chances for running tickless are maximized when 117 the task mostly runs in userspace and has few kernel activity. 118 119 You need to fill up the nohz_full boot parameter with the 120 desired range of dynticks CPUs. 121 122 This is implemented at the expense of some overhead in user <-> kernel 123 transitions: syscalls, exceptions and interrupts. Even when it's 124 dynamically off. 125 126 Say N. 127 128endchoice 129 130config CONTEXT_TRACKING 131 bool 132 133config CONTEXT_TRACKING_FORCE 134 bool "Force context tracking" 135 depends on CONTEXT_TRACKING 136 default y if !NO_HZ_FULL 137 help 138 The major pre-requirement for full dynticks to work is to 139 support the context tracking subsystem. But there are also 140 other dependencies to provide in order to make the full 141 dynticks working. 142 143 This option stands for testing when an arch implements the 144 context tracking backend but doesn't yet fullfill all the 145 requirements to make the full dynticks feature working. 146 Without the full dynticks, there is no way to test the support 147 for context tracking and the subsystems that rely on it: RCU 148 userspace extended quiescent state and tickless cputime 149 accounting. This option copes with the absence of the full 150 dynticks subsystem by forcing the context tracking on all 151 CPUs in the system. 152 153 Say Y only if you're working on the development of an 154 architecture backend for the context tracking. 155 156 Say N otherwise, this option brings an overhead that you 157 don't want in production. 158 159config NO_HZ 160 bool "Old Idle dynticks config" 161 help 162 This is the old config entry that enables dynticks idle. 163 We keep it around for a little while to enforce backward 164 compatibility with older config files. 165 166config HIGH_RES_TIMERS 167 bool "High Resolution Timer Support" 168 select TICK_ONESHOT 169 help 170 This option enables high resolution timer support. If your 171 hardware is not capable then this option only increases 172 the size of the kernel image. 173 174endmenu 175endif 176