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 # Timekeeping vsyscall support
  16 config GENERIC_TIME_VSYSCALL
  17         bool
  18
  19 # Timekeeping vsyscall support
  20 config GENERIC_TIME_VSYSCALL_OLD
  21         bool
  22
  23 # ktime_t scalar 64bit nsec representation
  24 config KTIME_SCALAR
  25         bool
  26
  27 # Old style timekeeping
  28 config ARCH_USES_GETTIMEOFFSET
  29         bool
  30
  31 # The generic clock events infrastructure
  32 config GENERIC_CLOCKEVENTS
  33         bool
  34
  35 # Migration helper. Builds, but does not invoke
  36 config GENERIC_CLOCKEVENTS_BUILD
  37         bool
  38         default y
  39         depends on GENERIC_CLOCKEVENTS
  40
  41 # Architecture can handle broadcast in a driver-agnostic way
  42 config ARCH_HAS_TICK_BROADCAST
  43         bool
  44
  45 # Clockevents broadcasting infrastructure
  46 config GENERIC_CLOCKEVENTS_BROADCAST
  47         bool
  48         depends on GENERIC_CLOCKEVENTS
  49
  50 # Automatically adjust the min. reprogramming time for
  51 # clock event device
  52 config GENERIC_CLOCKEVENTS_MIN_ADJUST
  53         bool
  54
  55 # Generic update of CMOS clock
  56 config GENERIC_CMOS_UPDATE
  57         bool
  58
  59 if GENERIC_CLOCKEVENTS
  60 menu "Timers subsystem"
  61
  62 # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
  63 # only related to the tick functionality. Oneshot clockevent devices
  64 # are supported independ of this.
  65 config TICK_ONESHOT
  66         bool
  67
  68 config NO_HZ_COMMON
  69         bool
  70         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  71         select TICK_ONESHOT
  72
  73 choice
  74         prompt "Timer tick handling"
  75         default NO_HZ_IDLE if NO_HZ
  76
  77 config HZ_PERIODIC
  78         bool "Periodic timer ticks (constant rate, no dynticks)"
  79         help
  80           This option keeps the tick running periodically at a constant
  81           rate, even when the CPU doesn't need it.
  82
  83 config NO_HZ_IDLE
  84         bool "Idle dynticks system (tickless idle)"
  85         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  86         select NO_HZ_COMMON
  87         help
  88           This option enables a tickless idle system: timer interrupts
  89           will only trigger on an as-needed basis when the system is idle.
  90           This is usually interesting for energy saving.
  91
  92           Most of the time you want to say Y here.
  93
  94 config NO_HZ_FULL
  95         bool "Full dynticks system (tickless)"
  96         # NO_HZ_COMMON dependency
  97         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  98         # We need at least one periodic CPU for timekeeping
  99         depends on SMP
 100         # RCU_USER_QS dependency
 101         depends on HAVE_CONTEXT_TRACKING
 102         # VIRT_CPU_ACCOUNTING_GEN dependency
 103         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 104         select NO_HZ_COMMON
 105         select RCU_USER_QS
 106         select RCU_NOCB_CPU
 107         select VIRT_CPU_ACCOUNTING_GEN
 108         select IRQ_WORK
 109         help
 110          Adaptively try to shutdown the tick whenever possible, even when
 111          the CPU is running tasks. Typically this requires running a single
 112          task on the CPU. Chances for running tickless are maximized when
 113          the task mostly runs in userspace and has few kernel activity.
 114
 115          You need to fill up the nohz_full boot parameter with the
 116          desired range of dynticks CPUs.
 117
 118          This is implemented at the expense of some overhead in user <-> kernel
 119          transitions: syscalls, exceptions and interrupts. Even when it's
 120          dynamically off.
 121
 122          Say N.
 123
 124 endchoice
 125
 126 config NO_HZ_FULL_ALL
 127        bool "Full dynticks system on all CPUs by default"
 128        depends on NO_HZ_FULL
 129        help
 130          If the user doesn't pass the nohz_full boot option to
 131          define the range of full dynticks CPUs, consider that all
 132          CPUs in the system are full dynticks by default.
 133          Note the boot CPU will still be kept outside the range to
 134          handle the timekeeping duty.
 135
 136 config NO_HZ_FULL_SYSIDLE
 137         bool "Detect full-system idle state for full dynticks system"
 138         depends on NO_HZ_FULL
 139         default n
 140         help
 141          At least one CPU must keep the scheduling-clock tick running for
 142          timekeeping purposes whenever there is a non-idle CPU, where
 143          "non-idle" also includes dynticks CPUs as long as they are
 144          running non-idle tasks.  Because the underlying adaptive-tick
 145          support cannot distinguish between all CPUs being idle and
 146          all CPUs each running a single task in dynticks mode, the
 147          underlying support simply ensures that there is always a CPU
 148          handling the scheduling-clock tick, whether or not all CPUs
 149          are idle.  This Kconfig option enables scalable detection of
 150          the all-CPUs-idle state, thus allowing the scheduling-clock
 151          tick to be disabled when all CPUs are idle.  Note that scalable
 152          detection of the all-CPUs-idle state means that larger systems
 153          will be slower to declare the all-CPUs-idle state.
 154
 155          Say Y if you would like to help debug all-CPUs-idle detection.
 156
 157          Say N if you are unsure.
 158
 159 config NO_HZ_FULL_SYSIDLE_SMALL
 160         int "Number of CPUs above which large-system approach is used"
 161         depends on NO_HZ_FULL_SYSIDLE
 162         range 1 NR_CPUS
 163         default 8
 164         help
 165          The full-system idle detection mechanism takes a lazy approach
 166          on large systems, as is required to attain decent scalability.
 167          However, on smaller systems, scalability is not anywhere near as
 168          large a concern as is energy efficiency.  The sysidle subsystem
 169          therefore uses a fast but non-scalable algorithm for small
 170          systems and a lazier but scalable algorithm for large systems.
 171          This Kconfig parameter defines the number of CPUs in the largest
 172          system that will be considered to be "small".
 173
 174          The default value will be fine in most cases.  Battery-powered
 175          systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
 176          numbers of CPUs, and (3) are suffering from battery-lifetime
 177          problems due to long sysidle latencies might wish to experiment
 178          with larger values for this Kconfig parameter.  On the other
 179          hand, they might be even better served by disabling NO_HZ_FULL
 180          entirely, given that NO_HZ_FULL is intended for HPC and
 181          real-time workloads that at present do not tend to be run on
 182          battery-powered systems.
 183
 184          Take the default if you are unsure.
 185
 186 config NO_HZ
 187         bool "Old Idle dynticks config"
 188         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 189         help
 190           This is the old config entry that enables dynticks idle.
 191           We keep it around for a little while to enforce backward
 192           compatibility with older config files.
 193
 194 config HIGH_RES_TIMERS
 195         bool "High Resolution Timer Support"
 196         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 197         select TICK_ONESHOT
 198         help
 199           This option enables high resolution timer support. If your
 200           hardware is not capable then this option only increases
 201           the size of the kernel image.
 202
 203 endmenu
 204 endif