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#
# 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
# 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
# Timekeeping vsyscall support
config GENERIC_TIME_VSYSCALL_OLD
bool
# Old style timekeeping
config ARCH_USES_GETTIMEOFFSET
bool
# The generic clock events infrastructure
config GENERIC_CLOCKEVENTS
bool
# 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
# 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
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 independ of this.
config TICK_ONESHOT
bool
config NO_HZ_COMMON
bool
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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)"
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
# We need at least one periodic CPU for timekeeping
depends on SMP
depends on HAVE_CONTEXT_TRACKING
# 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
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.
This is implemented at the expense of some overhead in user <-> kernel
transitions: syscalls, exceptions and interrupts. Even when it's
dynamically off.
Say N.
endchoice
config NO_HZ_FULL_ALL
bool "Full dynticks system on all CPUs by default (except CPU 0)"
depends on NO_HZ_FULL
help
If the user doesn't pass the nohz_full boot option to
define the range of full dynticks CPUs, consider that all
CPUs in the system are full dynticks by default.
Note the boot CPU will still be kept outside the range to
handle the timekeeping duty.
config NO_HZ_FULL_SYSIDLE
bool "Detect full-system idle state for full dynticks system"
depends on NO_HZ_FULL
default n
help
At least one CPU must keep the scheduling-clock tick running for
timekeeping purposes whenever there is a non-idle CPU, where
"non-idle" also includes dynticks CPUs as long as they are
running non-idle tasks. Because the underlying adaptive-tick
support cannot distinguish between all CPUs being idle and
all CPUs each running a single task in dynticks mode, the
underlying support simply ensures that there is always a CPU
handling the scheduling-clock tick, whether or not all CPUs
are idle. This Kconfig option enables scalable detection of
the all-CPUs-idle state, thus allowing the scheduling-clock
tick to be disabled when all CPUs are idle. Note that scalable
detection of the all-CPUs-idle state means that larger systems
will be slower to declare the all-CPUs-idle state.
Say Y if you would like to help debug all-CPUs-idle detection.
Say N if you are unsure.
config NO_HZ_FULL_SYSIDLE_SMALL
int "Number of CPUs above which large-system approach is used"
depends on NO_HZ_FULL_SYSIDLE
range 1 NR_CPUS
default 8
help
The full-system idle detection mechanism takes a lazy approach
on large systems, as is required to attain decent scalability.
However, on smaller systems, scalability is not anywhere near as
large a concern as is energy efficiency. The sysidle subsystem
therefore uses a fast but non-scalable algorithm for small
systems and a lazier but scalable algorithm for large systems.
This Kconfig parameter defines the number of CPUs in the largest
system that will be considered to be "small".
The default value will be fine in most cases. Battery-powered
systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
numbers of CPUs, and (3) are suffering from battery-lifetime
problems due to long sysidle latencies might wish to experiment
with larger values for this Kconfig parameter. On the other
hand, they might be even better served by disabling NO_HZ_FULL
entirely, given that NO_HZ_FULL is intended for HPC and
real-time workloads that at present do not tend to be run on
battery-powered systems.
Take the default if you are unsure.
config NO_HZ
bool "Old Idle dynticks config"
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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"
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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.
endmenu
endif
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