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# SPDX-License-Identifier: GPL-2.0-only
#
# Timer subsystem related configuration options
#
# Options selectable by arch Kconfig
# Watchdog function for clocksources to detect instabilities
config CLOCKSOURCE_WATCHDOG
bool
# Architecture has extra clocksource data
config ARCH_CLOCKSOURCE_DATA
bool
# Architecture has extra clocksource init called from registration
config ARCH_CLOCKSOURCE_INIT
bool
# Clocksources require validation of the clocksource against the last
# cycle update - x86/TSC misfeature
config CLOCKSOURCE_VALIDATE_LAST_CYCLE
bool
# Timekeeping vsyscall support
config GENERIC_TIME_VSYSCALL
bool
# The generic clock events infrastructure
config GENERIC_CLOCKEVENTS
def_bool !LEGACY_TIMER_TICK
# Architecture can handle broadcast in a driver-agnostic way
config ARCH_HAS_TICK_BROADCAST
bool
# Clockevents broadcasting infrastructure
config GENERIC_CLOCKEVENTS_BROADCAST
bool
depends on GENERIC_CLOCKEVENTS
# Handle broadcast in default_idle_call()
config GENERIC_CLOCKEVENTS_BROADCAST_IDLE
bool
depends on GENERIC_CLOCKEVENTS_BROADCAST
# Automatically adjust the min. reprogramming time for
# clock event device
config GENERIC_CLOCKEVENTS_MIN_ADJUST
bool
# Generic update of CMOS clock
config GENERIC_CMOS_UPDATE
bool
# Select to handle posix CPU timers from task_work
# and not from the timer interrupt context
config HAVE_POSIX_CPU_TIMERS_TASK_WORK
bool
config POSIX_CPU_TIMERS_TASK_WORK
bool
default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
config LEGACY_TIMER_TICK
bool
help
The legacy timer tick helper is used by platforms that
lack support for the generic clockevent framework.
New platforms should use generic clockevents instead.
config TIME_KUNIT_TEST
tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
depends on KUNIT
default KUNIT_ALL_TESTS
help
Enable this option to test RTC library functions.
If unsure, say N.
config CONTEXT_TRACKING
bool
config CONTEXT_TRACKING_IDLE
bool
select CONTEXT_TRACKING
help
Tracks idle state on behalf of RCU.
if GENERIC_CLOCKEVENTS
menu "Timers subsystem"
# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
# only related to the tick functionality. Oneshot clockevent devices
# are supported independent of this.
config TICK_ONESHOT
bool
config NO_HZ_COMMON
bool
select TICK_ONESHOT
choice
prompt "Timer tick handling"
default NO_HZ_IDLE if NO_HZ
config HZ_PERIODIC
bool "Periodic timer ticks (constant rate, no dynticks)"
help
This option keeps the tick running periodically at a constant
rate, even when the CPU doesn't need it.
config NO_HZ_IDLE
bool "Idle dynticks system (tickless idle)"
select NO_HZ_COMMON
help
This option enables a tickless idle system: timer interrupts
will only trigger on an as-needed basis when the system is idle.
This is usually interesting for energy saving.
Most of the time you want to say Y here.
config NO_HZ_FULL
bool "Full dynticks system (tickless)"
# NO_HZ_COMMON dependency
# We need at least one periodic CPU for timekeeping
depends on SMP
depends on HAVE_CONTEXT_TRACKING_USER
# VIRT_CPU_ACCOUNTING_GEN dependency
depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
select NO_HZ_COMMON
select RCU_NOCB_CPU
select VIRT_CPU_ACCOUNTING_GEN
select IRQ_WORK
select CPU_ISOLATION
help
Adaptively try to shutdown the tick whenever possible, even when
the CPU is running tasks. Typically this requires running a single
task on the CPU. Chances for running tickless are maximized when
the task mostly runs in userspace and has few kernel activity.
You need to fill up the nohz_full boot parameter with the
desired range of dynticks CPUs to use it. This is implemented at
the expense of some overhead in user <-> kernel transitions:
syscalls, exceptions and interrupts.
By default, without passing the nohz_full parameter, this behaves just
like NO_HZ_IDLE.
If you're a distro say Y.
endchoice
config CONTEXT_TRACKING_USER
bool
depends on HAVE_CONTEXT_TRACKING_USER
select CONTEXT_TRACKING
help
Track transitions between kernel and user on behalf of RCU and
tickless cputime accounting. The former case relies on context
tracking to enter/exit RCU extended quiescent states.
config CONTEXT_TRACKING_USER_FORCE
bool "Force user context tracking"
depends on CONTEXT_TRACKING_USER
default y if !NO_HZ_FULL
help
The major pre-requirement for full dynticks to work is to
support the user context tracking subsystem. But there are also
other dependencies to provide in order to make the full
dynticks working.
This option stands for testing when an arch implements the
user context tracking backend but doesn't yet fulfill all the
requirements to make the full dynticks feature working.
Without the full dynticks, there is no way to test the support
for user context tracking and the subsystems that rely on it: RCU
userspace extended quiescent state and tickless cputime
accounting. This option copes with the absence of the full
dynticks subsystem by forcing the user context tracking on all
CPUs in the system.
Say Y only if you're working on the development of an
architecture backend for the user context tracking.
Say N otherwise, this option brings an overhead that you
don't want in production.
config NO_HZ
bool "Old Idle dynticks config"
help
This is the old config entry that enables dynticks idle.
We keep it around for a little while to enforce backward
compatibility with older config files.
config HIGH_RES_TIMERS
bool "High Resolution Timer Support"
select TICK_ONESHOT
help
This option enables high resolution timer support. If your
hardware is not capable then this option only increases
the size of the kernel image.
config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
int "Clocksource watchdog maximum allowable skew (in μs)"
depends on CLOCKSOURCE_WATCHDOG
range 50 1000
default 125
help
Specify the maximum amount of allowable watchdog skew in
microseconds before reporting the clocksource to be unstable.
The default is based on a half-second clocksource watchdog
interval and NTP's maximum frequency drift of 500 parts
per million. If the clocksource is good enough for NTP,
it is good enough for the clocksource watchdog!
endmenu
endif
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