kernel/time/Kconfig

   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
   9 config CLOCKSOURCE_WATCHDOG
  10         bool
  11
  12 # Architecture has extra clocksource data
  13 config ARCH_CLOCKSOURCE_DATA
  14         bool
  15
  16 # Architecture has extra clocksource init called from registration
  17 config ARCH_CLOCKSOURCE_INIT
  18         bool
  19
  20 # Clocksources require validation of the clocksource against the last
  21 # cycle update - x86/TSC misfeature
  22 config CLOCKSOURCE_VALIDATE_LAST_CYCLE
  23         bool
  24
  25 # Timekeeping vsyscall support
  26 config GENERIC_TIME_VSYSCALL
  27         bool
  28
  29 # Old style timekeeping
  30 config ARCH_USES_GETTIMEOFFSET
  31         bool
  32
  33 # The generic clock events infrastructure
  34 config GENERIC_CLOCKEVENTS
  35         bool
  36
  37 # Architecture can handle broadcast in a driver-agnostic way
  38 config ARCH_HAS_TICK_BROADCAST
  39         bool
  40
  41 # Clockevents broadcasting infrastructure
  42 config GENERIC_CLOCKEVENTS_BROADCAST
  43         bool
  44         depends on GENERIC_CLOCKEVENTS
  45
  46 # Automatically adjust the min. reprogramming time for
  47 # clock event device
  48 config GENERIC_CLOCKEVENTS_MIN_ADJUST
  49         bool
  50
  51 # Generic update of CMOS clock
  52 config GENERIC_CMOS_UPDATE
  53         bool
  54
  55 if GENERIC_CLOCKEVENTS
  56 menu "Timers subsystem"
  57
  58 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
  59 # only related to the tick functionality. Oneshot clockevent devices
  60 # are supported independent of this.
  61 config TICK_ONESHOT
  62         bool
  63
  64 config NO_HZ_COMMON
  65         bool
  66         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  67         select TICK_ONESHOT
  68
  69 choice
  70         prompt "Timer tick handling"
  71         default NO_HZ_IDLE if NO_HZ
  72
  73 config HZ_PERIODIC
  74         bool "Periodic timer ticks (constant rate, no dynticks)"
  75         help
  76           This option keeps the tick running periodically at a constant
  77           rate, even when the CPU doesn't need it.
  78
  79 config NO_HZ_IDLE
  80         bool "Idle dynticks system (tickless idle)"
  81         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  82         select NO_HZ_COMMON
  83         help
  84           This option enables a tickless idle system: timer interrupts
  85           will only trigger on an as-needed basis when the system is idle.
  86           This is usually interesting for energy saving.
  87
  88           Most of the time you want to say Y here.
  89
  90 config NO_HZ_FULL
  91         bool "Full dynticks system (tickless)"
  92         # NO_HZ_COMMON dependency
  93         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  94         # We need at least one periodic CPU for timekeeping
  95         depends on SMP
  96         depends on HAVE_CONTEXT_TRACKING
  97         # VIRT_CPU_ACCOUNTING_GEN dependency
  98         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
  99         select NO_HZ_COMMON
 100         select RCU_NOCB_CPU
 101         select VIRT_CPU_ACCOUNTING_GEN
 102         select IRQ_WORK
 103         select CPU_ISOLATION
 104         help
 105          Adaptively try to shutdown the tick whenever possible, even when
 106          the CPU is running tasks. Typically this requires running a single
 107          task on the CPU. Chances for running tickless are maximized when
 108          the task mostly runs in userspace and has few kernel activity.
 109
 110          You need to fill up the nohz_full boot parameter with the
 111          desired range of dynticks CPUs.
 112
 113          This is implemented at the expense of some overhead in user <-> kernel
 114          transitions: syscalls, exceptions and interrupts. Even when it's
 115          dynamically off.
 116
 117          Say N.
 118
 119 endchoice
 120
 121 config CONTEXT_TRACKING
 122        bool
 123
 124 config CONTEXT_TRACKING_FORCE
 125         bool "Force context tracking"
 126         depends on CONTEXT_TRACKING
 127         default y if !NO_HZ_FULL
 128         help
 129           The major pre-requirement for full dynticks to work is to
 130           support the context tracking subsystem. But there are also
 131           other dependencies to provide in order to make the full
 132           dynticks working.
 133
 134           This option stands for testing when an arch implements the
 135           context tracking backend but doesn't yet fullfill all the
 136           requirements to make the full dynticks feature working.
 137           Without the full dynticks, there is no way to test the support
 138           for context tracking and the subsystems that rely on it: RCU
 139           userspace extended quiescent state and tickless cputime
 140           accounting. This option copes with the absence of the full
 141           dynticks subsystem by forcing the context tracking on all
 142           CPUs in the system.
 143
 144           Say Y only if you're working on the development of an
 145           architecture backend for the context tracking.
 146
 147           Say N otherwise, this option brings an overhead that you
 148           don't want in production.
 149
 150 config NO_HZ
 151         bool "Old Idle dynticks config"
 152         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 153         help
 154           This is the old config entry that enables dynticks idle.
 155           We keep it around for a little while to enforce backward
 156           compatibility with older config files.
 157
 158 config HIGH_RES_TIMERS
 159         bool "High Resolution Timer Support"
 160         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 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
 167 endmenu
 168 endif