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 # The generic clock events infrastructure
  30 config GENERIC_CLOCKEVENTS
  31         def_bool !LEGACY_TIMER_TICK
  32
  33 # Architecture can handle broadcast in a driver-agnostic way
  34 config ARCH_HAS_TICK_BROADCAST
  35         bool
  36
  37 # Clockevents broadcasting infrastructure
  38 config GENERIC_CLOCKEVENTS_BROADCAST
  39         bool
  40         depends on GENERIC_CLOCKEVENTS
  41
  42 # Automatically adjust the min. reprogramming time for
  43 # clock event device
  44 config GENERIC_CLOCKEVENTS_MIN_ADJUST
  45         bool
  46
  47 # Generic update of CMOS clock
  48 config GENERIC_CMOS_UPDATE
  49         bool
  50
  51 # Select to handle posix CPU timers from task_work
  52 # and not from the timer interrupt context
  53 config HAVE_POSIX_CPU_TIMERS_TASK_WORK
  54         bool
  55
  56 config POSIX_CPU_TIMERS_TASK_WORK
  57         bool
  58         default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
  59
  60 config 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
  67 if GENERIC_CLOCKEVENTS
  68 menu "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.
  73 config TICK_ONESHOT
  74         bool
  75
  76 config NO_HZ_COMMON
  77         bool
  78         select TICK_ONESHOT
  79
  80 choice
  81         prompt "Timer tick handling"
  82         default NO_HZ_IDLE if NO_HZ
  83
  84 config 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
  90 config 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
 100 config 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
 128 endchoice
 129
 130 config CONTEXT_TRACKING
 131        bool
 132
 133 config 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
 159 config 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
 166 config 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
 174 endmenu
 175 endif