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         # RCU_USER_QS dependency
  96         depends on HAVE_CONTEXT_TRACKING
  97         # VIRT_CPU_ACCOUNTING_GEN dependency
  98         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
  99         select NO_HZ_COMMON
 100         select RCU_USER_QS
 101         select RCU_NOCB_CPU
 102         select VIRT_CPU_ACCOUNTING_GEN
 103         select IRQ_WORK
 104         help
 105          Adaptively try to shutdown the tick whenever possible, even when
 106          the CPU is running tasks. Typically this requires running a single
 107          task on the CPU. Chances for running tickless are maximized when
 108          the task mostly runs in userspace and has few kernel activity.
 109
 110          You need to fill up the nohz_full boot parameter with the
 111          desired range of dynticks CPUs.
 112
 113          This is implemented at the expense of some overhead in user <-> kernel
 114          transitions: syscalls, exceptions and interrupts. Even when it's
 115          dynamically off.
 116
 117          Say N.
 118
 119 endchoice
 120
 121 config NO_HZ_FULL_ALL
 122        bool "Full dynticks system on all CPUs by default (except CPU 0)"
 123        depends on NO_HZ_FULL
 124        help
 125          If the user doesn't pass the nohz_full boot option to
 126          define the range of full dynticks CPUs, consider that all
 127          CPUs in the system are full dynticks by default.
 128          Note the boot CPU will still be kept outside the range to
 129          handle the timekeeping duty.
 130
 131 config NO_HZ_FULL_SYSIDLE
 132         bool "Detect full-system idle state for full dynticks system"
 133         depends on NO_HZ_FULL
 134         default n
 135         help
 136          At least one CPU must keep the scheduling-clock tick running for
 137          timekeeping purposes whenever there is a non-idle CPU, where
 138          "non-idle" also includes dynticks CPUs as long as they are
 139          running non-idle tasks.  Because the underlying adaptive-tick
 140          support cannot distinguish between all CPUs being idle and
 141          all CPUs each running a single task in dynticks mode, the
 142          underlying support simply ensures that there is always a CPU
 143          handling the scheduling-clock tick, whether or not all CPUs
 144          are idle.  This Kconfig option enables scalable detection of
 145          the all-CPUs-idle state, thus allowing the scheduling-clock
 146          tick to be disabled when all CPUs are idle.  Note that scalable
 147          detection of the all-CPUs-idle state means that larger systems
 148          will be slower to declare the all-CPUs-idle state.
 149
 150          Say Y if you would like to help debug all-CPUs-idle detection.
 151
 152          Say N if you are unsure.
 153
 154 config NO_HZ_FULL_SYSIDLE_SMALL
 155         int "Number of CPUs above which large-system approach is used"
 156         depends on NO_HZ_FULL_SYSIDLE
 157         range 1 NR_CPUS
 158         default 8
 159         help
 160          The full-system idle detection mechanism takes a lazy approach
 161          on large systems, as is required to attain decent scalability.
 162          However, on smaller systems, scalability is not anywhere near as
 163          large a concern as is energy efficiency.  The sysidle subsystem
 164          therefore uses a fast but non-scalable algorithm for small
 165          systems and a lazier but scalable algorithm for large systems.
 166          This Kconfig parameter defines the number of CPUs in the largest
 167          system that will be considered to be "small".
 168
 169          The default value will be fine in most cases.  Battery-powered
 170          systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
 171          numbers of CPUs, and (3) are suffering from battery-lifetime
 172          problems due to long sysidle latencies might wish to experiment
 173          with larger values for this Kconfig parameter.  On the other
 174          hand, they might be even better served by disabling NO_HZ_FULL
 175          entirely, given that NO_HZ_FULL is intended for HPC and
 176          real-time workloads that at present do not tend to be run on
 177          battery-powered systems.
 178
 179          Take the default if you are unsure.
 180
 181 config NO_HZ
 182         bool "Old Idle dynticks config"
 183         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 184         help
 185           This is the old config entry that enables dynticks idle.
 186           We keep it around for a little while to enforce backward
 187           compatibility with older config files.
 188
 189 config HIGH_RES_TIMERS
 190         bool "High Resolution Timer Support"
 191         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 192         select TICK_ONESHOT
 193         help
 194           This option enables high resolution timer support. If your
 195           hardware is not capable then this option only increases
 196           the size of the kernel image.
 197
 198 endmenu
 199 endif