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 # Timekeeping vsyscall support
  25 config GENERIC_TIME_VSYSCALL_OLD
  26         bool
  27
  28 # Old style timekeeping
  29 config ARCH_USES_GETTIMEOFFSET
  30         bool
  31
  32 # The generic clock events infrastructure
  33 config GENERIC_CLOCKEVENTS
  34         bool
  35
  36 # Architecture can handle broadcast in a driver-agnostic way
  37 config ARCH_HAS_TICK_BROADCAST
  38         bool
  39
  40 # Clockevents broadcasting infrastructure
  41 config GENERIC_CLOCKEVENTS_BROADCAST
  42         bool
  43         depends on GENERIC_CLOCKEVENTS
  44
  45 # Automatically adjust the min. reprogramming time for
  46 # clock event device
  47 config GENERIC_CLOCKEVENTS_MIN_ADJUST
  48         bool
  49
  50 # Generic update of CMOS clock
  51 config GENERIC_CMOS_UPDATE
  52         bool
  53
  54 if GENERIC_CLOCKEVENTS
  55 menu "Timers subsystem"
  56
  57 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
  58 # only related to the tick functionality. Oneshot clockevent devices
  59 # are supported independ of this.
  60 config TICK_ONESHOT
  61         bool
  62
  63 config NO_HZ_COMMON
  64         bool
  65         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  66         select TICK_ONESHOT
  67
  68 choice
  69         prompt "Timer tick handling"
  70         default NO_HZ_IDLE if NO_HZ
  71
  72 config HZ_PERIODIC
  73         bool "Periodic timer ticks (constant rate, no dynticks)"
  74         help
  75           This option keeps the tick running periodically at a constant
  76           rate, even when the CPU doesn't need it.
  77
  78 config NO_HZ_IDLE
  79         bool "Idle dynticks system (tickless idle)"
  80         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  81         select NO_HZ_COMMON
  82         help
  83           This option enables a tickless idle system: timer interrupts
  84           will only trigger on an as-needed basis when the system is idle.
  85           This is usually interesting for energy saving.
  86
  87           Most of the time you want to say Y here.
  88
  89 config NO_HZ_FULL
  90         bool "Full dynticks system (tickless)"
  91         # NO_HZ_COMMON dependency
  92         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  93         # We need at least one periodic CPU for timekeeping
  94         depends on SMP
  95         depends on HAVE_CONTEXT_TRACKING
  96         # VIRT_CPU_ACCOUNTING_GEN dependency
  97         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
  98         select NO_HZ_COMMON
  99         select RCU_NOCB_CPU
 100         select VIRT_CPU_ACCOUNTING_GEN
 101         select IRQ_WORK
 102         help
 103          Adaptively try to shutdown the tick whenever possible, even when
 104          the CPU is running tasks. Typically this requires running a single
 105          task on the CPU. Chances for running tickless are maximized when
 106          the task mostly runs in userspace and has few kernel activity.
 107
 108          You need to fill up the nohz_full boot parameter with the
 109          desired range of dynticks CPUs.
 110
 111          This is implemented at the expense of some overhead in user <-> kernel
 112          transitions: syscalls, exceptions and interrupts. Even when it's
 113          dynamically off.
 114
 115          Say N.
 116
 117 endchoice
 118
 119 config NO_HZ_FULL_ALL
 120        bool "Full dynticks system on all CPUs by default (except CPU 0)"
 121        depends on NO_HZ_FULL
 122        help
 123          If the user doesn't pass the nohz_full boot option to
 124          define the range of full dynticks CPUs, consider that all
 125          CPUs in the system are full dynticks by default.
 126          Note the boot CPU will still be kept outside the range to
 127          handle the timekeeping duty.
 128
 129 config NO_HZ
 130         bool "Old Idle dynticks config"
 131         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 132         help
 133           This is the old config entry that enables dynticks idle.
 134           We keep it around for a little while to enforce backward
 135           compatibility with older config files.
 136
 137 config HIGH_RES_TIMERS
 138         bool "High Resolution Timer Support"
 139         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 140         select TICK_ONESHOT
 141         help
 142           This option enables high resolution timer support. If your
 143           hardware is not capable then this option only increases
 144           the size of the kernel image.
 145
 146 endmenu
 147 endif