linux-imx/kernel/time/Kconfig

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