6832d9652f
Pull timers/nohz changes from Ingo Molnar: "It mostly contains fixes and full dynticks off-case optimizations, by Frederic Weisbecker" * 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits) nohz: Include local CPU in full dynticks global kick nohz: Optimize full dynticks's sched hooks with static keys nohz: Optimize full dynticks state checks with static keys nohz: Rename a few state variables vtime: Always debug check snapshot source _before_ updating it vtime: Always scale generic vtime accounting results vtime: Optimize full dynticks accounting off case with static keys vtime: Describe overriden functions in dedicated arch headers m68k: hardirq_count() only need preempt_mask.h hardirq: Split preempt count mask definitions context_tracking: Split low level state headers vtime: Fix racy cputime delta update vtime: Remove a few unneeded generic vtime state checks context_tracking: User/kernel broundary cross trace events context_tracking: Optimize context switch off case with static keys context_tracking: Optimize guest APIs off case with static key context_tracking: Optimize main APIs off case with static key context_tracking: Ground setup for static key use context_tracking: Remove full dynticks' hacky dependency on wide context tracking nohz: Only enable context tracking on full dynticks CPUs ...
6.2 KiB
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
Timekeeping vsyscall support
config GENERIC_TIME_VSYSCALL bool
Timekeeping vsyscall support
config GENERIC_TIME_VSYSCALL_OLD bool
ktime_t scalar 64bit nsec representation
config KTIME_SCALAR bool
Old style timekeeping
config ARCH_USES_GETTIMEOFFSET bool
The generic clock events infrastructure
config GENERIC_CLOCKEVENTS bool
Migration helper. Builds, but does not invoke
config GENERIC_CLOCKEVENTS_BUILD bool default y depends on GENERIC_CLOCKEVENTS
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 # RCU_USER_QS dependency depends on HAVE_CONTEXT_TRACKING # VIRT_CPU_ACCOUNTING_GEN dependency depends on 64BIT select NO_HZ_COMMON select RCU_USER_QS 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" 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