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 bool 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 60if GENERIC_CLOCKEVENTS 61menu "Timers subsystem" 62 63# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 64# only related to the tick functionality. Oneshot clockevent devices 65# are supported independent of this. 66config TICK_ONESHOT 67 bool 68 69config NO_HZ_COMMON 70 bool 71 select TICK_ONESHOT 72 73choice 74 prompt "Timer tick handling" 75 default NO_HZ_IDLE if NO_HZ 76 77config HZ_PERIODIC 78 bool "Periodic timer ticks (constant rate, no dynticks)" 79 help 80 This option keeps the tick running periodically at a constant 81 rate, even when the CPU doesn't need it. 82 83config NO_HZ_IDLE 84 bool "Idle dynticks system (tickless idle)" 85 select NO_HZ_COMMON 86 help 87 This option enables a tickless idle system: timer interrupts 88 will only trigger on an as-needed basis when the system is idle. 89 This is usually interesting for energy saving. 90 91 Most of the time you want to say Y here. 92 93config NO_HZ_FULL 94 bool "Full dynticks system (tickless)" 95 # NO_HZ_COMMON dependency 96 # We need at least one periodic CPU for timekeeping 97 depends on SMP 98 depends on HAVE_CONTEXT_TRACKING 99 # VIRT_CPU_ACCOUNTING_GEN dependency 100 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 101 select NO_HZ_COMMON 102 select RCU_NOCB_CPU 103 select VIRT_CPU_ACCOUNTING_GEN 104 select IRQ_WORK 105 select CPU_ISOLATION 106 help 107 Adaptively try to shutdown the tick whenever possible, even when 108 the CPU is running tasks. Typically this requires running a single 109 task on the CPU. Chances for running tickless are maximized when 110 the task mostly runs in userspace and has few kernel activity. 111 112 You need to fill up the nohz_full boot parameter with the 113 desired range of dynticks CPUs. 114 115 This is implemented at the expense of some overhead in user <-> kernel 116 transitions: syscalls, exceptions and interrupts. Even when it's 117 dynamically off. 118 119 Say N. 120 121endchoice 122 123config CONTEXT_TRACKING 124 bool 125 126config CONTEXT_TRACKING_FORCE 127 bool "Force context tracking" 128 depends on CONTEXT_TRACKING 129 default y if !NO_HZ_FULL 130 help 131 The major pre-requirement for full dynticks to work is to 132 support the context tracking subsystem. But there are also 133 other dependencies to provide in order to make the full 134 dynticks working. 135 136 This option stands for testing when an arch implements the 137 context tracking backend but doesn't yet fullfill all the 138 requirements to make the full dynticks feature working. 139 Without the full dynticks, there is no way to test the support 140 for context tracking and the subsystems that rely on it: RCU 141 userspace extended quiescent state and tickless cputime 142 accounting. This option copes with the absence of the full 143 dynticks subsystem by forcing the context tracking on all 144 CPUs in the system. 145 146 Say Y only if you're working on the development of an 147 architecture backend for the context tracking. 148 149 Say N otherwise, this option brings an overhead that you 150 don't want in production. 151 152config NO_HZ 153 bool "Old Idle dynticks config" 154 help 155 This is the old config entry that enables dynticks idle. 156 We keep it around for a little while to enforce backward 157 compatibility with older config files. 158 159config HIGH_RES_TIMERS 160 bool "High Resolution Timer Support" 161 select TICK_ONESHOT 162 help 163 This option enables high resolution timer support. If your 164 hardware is not capable then this option only increases 165 the size of the kernel image. 166 167endmenu 168endif 169