LXR linux/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
   8config CLOCKSOURCE_WATCHDOG
   9        bool
  10
  11# Architecture has extra clocksource data
  12config ARCH_CLOCKSOURCE_DATA
  13        bool
  14
  15# Clocksources require validation of the clocksource against the last
  16# cycle update - x86/TSC misfeature
  17config CLOCKSOURCE_VALIDATE_LAST_CYCLE
  18        bool
  19
  20# Timekeeping vsyscall support
  21config GENERIC_TIME_VSYSCALL
  22        bool
  23
  24# Timekeeping vsyscall support
  25config GENERIC_TIME_VSYSCALL_OLD
  26        bool
  27
  28# Old style timekeeping
  29config ARCH_USES_GETTIMEOFFSET
  30        bool
  31
  32# The generic clock events infrastructure
  33config GENERIC_CLOCKEVENTS
  34        bool
  35
  36# Architecture can handle broadcast in a driver-agnostic way
  37config ARCH_HAS_TICK_BROADCAST
  38        bool
  39
  40# Clockevents broadcasting infrastructure
  41config GENERIC_CLOCKEVENTS_BROADCAST
  42        bool
  43        depends on GENERIC_CLOCKEVENTS
  44
  45# Automatically adjust the min. reprogramming time for
  46# clock event device
  47config GENERIC_CLOCKEVENTS_MIN_ADJUST
  48        bool
  49
  50# Generic update of CMOS clock
  51config GENERIC_CMOS_UPDATE
  52        bool
  53
  54if GENERIC_CLOCKEVENTS
  55menu "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.
  60config TICK_ONESHOT
  61        bool
  62
  63config NO_HZ_COMMON
  64        bool
  65        depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
  66        select TICK_ONESHOT
  67
  68choice
  69        prompt "Timer tick handling"
  70        default NO_HZ_IDLE if NO_HZ
  71
  72config 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
  78config 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
  89config 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
 117endchoice
 118
 119config 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
 129config NO_HZ_FULL_SYSIDLE
 130        bool "Detect full-system idle state for full dynticks system"
 131        depends on NO_HZ_FULL
 132        default n
 133        help
 134         At least one CPU must keep the scheduling-clock tick running for
 135         timekeeping purposes whenever there is a non-idle CPU, where
 136         "non-idle" also includes dynticks CPUs as long as they are
 137         running non-idle tasks.  Because the underlying adaptive-tick
 138         support cannot distinguish between all CPUs being idle and
 139         all CPUs each running a single task in dynticks mode, the
 140         underlying support simply ensures that there is always a CPU
 141         handling the scheduling-clock tick, whether or not all CPUs
 142         are idle.  This Kconfig option enables scalable detection of
 143         the all-CPUs-idle state, thus allowing the scheduling-clock
 144         tick to be disabled when all CPUs are idle.  Note that scalable
 145         detection of the all-CPUs-idle state means that larger systems
 146         will be slower to declare the all-CPUs-idle state.
 147
 148         Say Y if you would like to help debug all-CPUs-idle detection.
 149
 150         Say N if you are unsure.
 151
 152config NO_HZ_FULL_SYSIDLE_SMALL
 153        int "Number of CPUs above which large-system approach is used"
 154        depends on NO_HZ_FULL_SYSIDLE
 155        range 1 NR_CPUS
 156        default 8
 157        help
 158         The full-system idle detection mechanism takes a lazy approach
 159         on large systems, as is required to attain decent scalability.
 160         However, on smaller systems, scalability is not anywhere near as
 161         large a concern as is energy efficiency.  The sysidle subsystem
 162         therefore uses a fast but non-scalable algorithm for small
 163         systems and a lazier but scalable algorithm for large systems.
 164         This Kconfig parameter defines the number of CPUs in the largest
 165         system that will be considered to be "small".
 166
 167         The default value will be fine in most cases.  Battery-powered
 168         systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
 169         numbers of CPUs, and (3) are suffering from battery-lifetime
 170         problems due to long sysidle latencies might wish to experiment
 171         with larger values for this Kconfig parameter.  On the other
 172         hand, they might be even better served by disabling NO_HZ_FULL
 173         entirely, given that NO_HZ_FULL is intended for HPC and
 174         real-time workloads that at present do not tend to be run on
 175         battery-powered systems.
 176
 177         Take the default if you are unsure.
 178
 179config NO_HZ
 180        bool "Old Idle dynticks config"
 181        depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 182        help
 183          This is the old config entry that enables dynticks idle.
 184          We keep it around for a little while to enforce backward
 185          compatibility with older config files.
 186
 187config HIGH_RES_TIMERS
 188        bool "High Resolution Timer Support"
 189        depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 190        select TICK_ONESHOT
 191        help
 192          This option enables high resolution timer support. If your
 193          hardware is not capable then this option only increases
 194          the size of the kernel image.
 195
 196endmenu
 197endif
 198