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 # Migration helper. Builds, but does not invoke
  37 config GENERIC_CLOCKEVENTS_BUILD
  38         bool
  39         default y
  40         depends on GENERIC_CLOCKEVENTS
  41
  42 # Architecture can handle broadcast in a driver-agnostic way
  43 config ARCH_HAS_TICK_BROADCAST
  44         bool
  45
  46 # Clockevents broadcasting infrastructure
  47 config GENERIC_CLOCKEVENTS_BROADCAST
  48         bool
  49         depends on GENERIC_CLOCKEVENTS
  50
  51 # Automatically adjust the min. reprogramming time for
  52 # clock event device
  53 config GENERIC_CLOCKEVENTS_MIN_ADJUST
  54         bool
  55
  56 # Generic update of CMOS clock
  57 config GENERIC_CMOS_UPDATE
  58         bool
  59
  60 if GENERIC_CLOCKEVENTS
  61 menu "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 independ of this.
  66 config TICK_ONESHOT
  67         bool
  68
  69 config NO_HZ_COMMON
  70         bool
  71         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  72         select TICK_ONESHOT
  73
  74 choice
  75         prompt "Timer tick handling"
  76         default NO_HZ_IDLE if NO_HZ
  77
  78 config HZ_PERIODIC
  79         bool "Periodic timer ticks (constant rate, no dynticks)"
  80         help
  81           This option keeps the tick running periodically at a constant
  82           rate, even when the CPU doesn't need it.
  83
  84 config NO_HZ_IDLE
  85         bool "Idle dynticks system (tickless idle)"
  86         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  87         select NO_HZ_COMMON
  88         help
  89           This option enables a tickless idle system: timer interrupts
  90           will only trigger on an as-needed basis when the system is idle.
  91           This is usually interesting for energy saving.
  92
  93           Most of the time you want to say Y here.
  94
  95 config NO_HZ_FULL
  96         bool "Full dynticks system (tickless)"
  97         # NO_HZ_COMMON dependency
  98         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  99         # We need at least one periodic CPU for timekeeping
 100         depends on SMP
 101         # RCU_USER_QS dependency
 102         depends on HAVE_CONTEXT_TRACKING
 103         # VIRT_CPU_ACCOUNTING_GEN dependency
 104         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 105         select NO_HZ_COMMON
 106         select RCU_USER_QS
 107         select RCU_NOCB_CPU
 108         select VIRT_CPU_ACCOUNTING_GEN
 109         select IRQ_WORK
 110         help
 111          Adaptively try to shutdown the tick whenever possible, even when
 112          the CPU is running tasks. Typically this requires running a single
 113          task on the CPU. Chances for running tickless are maximized when
 114          the task mostly runs in userspace and has few kernel activity.
 115
 116          You need to fill up the nohz_full boot parameter with the
 117          desired range of dynticks CPUs.
 118
 119          This is implemented at the expense of some overhead in user <-> kernel
 120          transitions: syscalls, exceptions and interrupts. Even when it's
 121          dynamically off.
 122
 123          Say N.
 124
 125 endchoice
 126
 127 config NO_HZ_FULL_ALL
 128        bool "Full dynticks system on all CPUs by default (except CPU 0)"
 129        depends on NO_HZ_FULL
 130        help
 131          If the user doesn't pass the nohz_full boot option to
 132          define the range of full dynticks CPUs, consider that all
 133          CPUs in the system are full dynticks by default.
 134          Note the boot CPU will still be kept outside the range to
 135          handle the timekeeping duty.
 136
 137 config NO_HZ_FULL_SYSIDLE
 138         bool "Detect full-system idle state for full dynticks system"
 139         depends on NO_HZ_FULL
 140         default n
 141         help
 142          At least one CPU must keep the scheduling-clock tick running for
 143          timekeeping purposes whenever there is a non-idle CPU, where
 144          "non-idle" also includes dynticks CPUs as long as they are
 145          running non-idle tasks.  Because the underlying adaptive-tick
 146          support cannot distinguish between all CPUs being idle and
 147          all CPUs each running a single task in dynticks mode, the
 148          underlying support simply ensures that there is always a CPU
 149          handling the scheduling-clock tick, whether or not all CPUs
 150          are idle.  This Kconfig option enables scalable detection of
 151          the all-CPUs-idle state, thus allowing the scheduling-clock
 152          tick to be disabled when all CPUs are idle.  Note that scalable
 153          detection of the all-CPUs-idle state means that larger systems
 154          will be slower to declare the all-CPUs-idle state.
 155
 156          Say Y if you would like to help debug all-CPUs-idle detection.
 157
 158          Say N if you are unsure.
 159
 160 config NO_HZ_FULL_SYSIDLE_SMALL
 161         int "Number of CPUs above which large-system approach is used"
 162         depends on NO_HZ_FULL_SYSIDLE
 163         range 1 NR_CPUS
 164         default 8
 165         help
 166          The full-system idle detection mechanism takes a lazy approach
 167          on large systems, as is required to attain decent scalability.
 168          However, on smaller systems, scalability is not anywhere near as
 169          large a concern as is energy efficiency.  The sysidle subsystem
 170          therefore uses a fast but non-scalable algorithm for small
 171          systems and a lazier but scalable algorithm for large systems.
 172          This Kconfig parameter defines the number of CPUs in the largest
 173          system that will be considered to be "small".
 174
 175          The default value will be fine in most cases.  Battery-powered
 176          systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
 177          numbers of CPUs, and (3) are suffering from battery-lifetime
 178          problems due to long sysidle latencies might wish to experiment
 179          with larger values for this Kconfig parameter.  On the other
 180          hand, they might be even better served by disabling NO_HZ_FULL
 181          entirely, given that NO_HZ_FULL is intended for HPC and
 182          real-time workloads that at present do not tend to be run on
 183          battery-powered systems.
 184
 185          Take the default if you are unsure.
 186
 187 config NO_HZ
 188         bool "Old Idle dynticks config"
 189         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 190         help
 191           This is the old config entry that enables dynticks idle.
 192           We keep it around for a little while to enforce backward
 193           compatibility with older config files.
 194
 195 config HIGH_RES_TIMERS
 196         bool "High Resolution Timer Support"
 197         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 198         select TICK_ONESHOT
 199         help
 200           This option enables high resolution timer support. If your
 201           hardware is not capable then this option only increases
 202           the size of the kernel image.
 203
 204 endmenu
 205 endif