kernel/time/Kconfig

   1 #
   2 # Timer subsystem related configuration options
   3 #
   4
   5 # Options selectable by arch Kconfig
   6
   7 # Watchdog function for clocksources to detect instabilities
   8 config CLOCKSOURCE_WATCHDOG
   9         bool
  10
  11 # Architecture has extra clocksource data
  12 config ARCH_CLOCKSOURCE_DATA
  13         bool
  14
  15 # Clocksources require validation of the clocksource against the last
  16 # cycle update - x86/TSC misfeature
  17 config CLOCKSOURCE_VALIDATE_LAST_CYCLE
  18         bool
  19
  20 # Timekeeping vsyscall support
  21 config GENERIC_TIME_VSYSCALL
  22         bool
  23
  24 # Old style timekeeping
  25 config ARCH_USES_GETTIMEOFFSET
  26         bool
  27
  28 # The generic clock events infrastructure
  29 config GENERIC_CLOCKEVENTS
  30         bool
  31
  32 # Architecture can handle broadcast in a driver-agnostic way
  33 config ARCH_HAS_TICK_BROADCAST
  34         bool
  35
  36 # Clockevents broadcasting infrastructure
  37 config GENERIC_CLOCKEVENTS_BROADCAST
  38         bool
  39         depends on GENERIC_CLOCKEVENTS
  40
  41 # Automatically adjust the min. reprogramming time for
  42 # clock event device
  43 config GENERIC_CLOCKEVENTS_MIN_ADJUST
  44         bool
  45
  46 # Generic update of CMOS clock
  47 config GENERIC_CMOS_UPDATE
  48         bool
  49
  50 if GENERIC_CLOCKEVENTS
  51 menu "Timers subsystem"
  52
  53 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
  54 # only related to the tick functionality. Oneshot clockevent devices
  55 # are supported independent of this.
  56 config TICK_ONESHOT
  57         bool
  58
  59 config NO_HZ_COMMON
  60         bool
  61         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  62         select TICK_ONESHOT
  63
  64 choice
  65         prompt "Timer tick handling"
  66         default NO_HZ_IDLE if NO_HZ
  67
  68 config HZ_PERIODIC
  69         bool "Periodic timer ticks (constant rate, no dynticks)"
  70         help
  71           This option keeps the tick running periodically at a constant
  72           rate, even when the CPU doesn't need it.
  73
  74 config NO_HZ_IDLE
  75         bool "Idle dynticks system (tickless idle)"
  76         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  77         select NO_HZ_COMMON
  78         help
  79           This option enables a tickless idle system: timer interrupts
  80           will only trigger on an as-needed basis when the system is idle.
  81           This is usually interesting for energy saving.
  82
  83           Most of the time you want to say Y here.
  84
  85 config NO_HZ_FULL
  86         bool "Full dynticks system (tickless)"
  87         # NO_HZ_COMMON dependency
  88         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  89         # We need at least one periodic CPU for timekeeping
  90         depends on SMP
  91         depends on HAVE_CONTEXT_TRACKING
  92         # VIRT_CPU_ACCOUNTING_GEN dependency
  93         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
  94         select NO_HZ_COMMON
  95         select RCU_NOCB_CPU
  96         select VIRT_CPU_ACCOUNTING_GEN
  97         select IRQ_WORK
  98         help
  99          Adaptively try to shutdown the tick whenever possible, even when
 100          the CPU is running tasks. Typically this requires running a single
 101          task on the CPU. Chances for running tickless are maximized when
 102          the task mostly runs in userspace and has few kernel activity.
 103
 104          You need to fill up the nohz_full boot parameter with the
 105          desired range of dynticks CPUs.
 106
 107          This is implemented at the expense of some overhead in user <-> kernel
 108          transitions: syscalls, exceptions and interrupts. Even when it's
 109          dynamically off.
 110
 111          Say N.
 112
 113 endchoice
 114
 115 config NO_HZ_FULL_ALL
 116        bool "Full dynticks system on all CPUs by default (except CPU 0)"
 117        depends on NO_HZ_FULL
 118        help
 119          If the user doesn't pass the nohz_full boot option to
 120          define the range of full dynticks CPUs, consider that all
 121          CPUs in the system are full dynticks by default.
 122          Note the boot CPU will still be kept outside the range to
 123          handle the timekeeping duty.
 124
 125 config NO_HZ
 126         bool "Old Idle dynticks config"
 127         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 128         help
 129           This is the old config entry that enables dynticks idle.
 130           We keep it around for a little while to enforce backward
 131           compatibility with older config files.
 132
 133 config HIGH_RES_TIMERS
 134         bool "High Resolution Timer Support"
 135         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 136         select TICK_ONESHOT
 137         help
 138           This option enables high resolution timer support. If your
 139           hardware is not capable then this option only increases
 140           the size of the kernel image.
 141
 142 endmenu
 143 endif