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09ec54429c
The only user of the cycle_last validation is the x86 TSC. In order to
provide NMI safe accessor functions for clock monotonic and
monotonic_raw we need to do that in the core.
We can't do the TSC specific
if (now < cycle_last)
now = cycle_last;
for the other wrapping around clocksources, but TSC has
CLOCKSOURCE_MASK(64) which actually does not mask out anything so if
now is less than cycle_last the subtraction will give a negative
result. So we can check for that in clocksource_delta() and return 0
for that case.
Implement and enable it for x86
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
205 lines
6.4 KiB
Text
205 lines
6.4 KiB
Text
#
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# Timer subsystem related configuration options
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#
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# Options selectable by arch Kconfig
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# Watchdog function for clocksources to detect instabilities
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config CLOCKSOURCE_WATCHDOG
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bool
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# Architecture has extra clocksource data
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config ARCH_CLOCKSOURCE_DATA
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bool
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# Clocksources require validation of the clocksource against the last
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# cycle update - x86/TSC misfeature
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config CLOCKSOURCE_VALIDATE_LAST_CYCLE
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bool
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# Timekeeping vsyscall support
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config GENERIC_TIME_VSYSCALL
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bool
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# Timekeeping vsyscall support
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config GENERIC_TIME_VSYSCALL_OLD
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bool
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# Old style timekeeping
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config ARCH_USES_GETTIMEOFFSET
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bool
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# The generic clock events infrastructure
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config GENERIC_CLOCKEVENTS
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bool
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# Migration helper. Builds, but does not invoke
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config GENERIC_CLOCKEVENTS_BUILD
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bool
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default y
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depends on GENERIC_CLOCKEVENTS
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# Architecture can handle broadcast in a driver-agnostic way
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config ARCH_HAS_TICK_BROADCAST
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bool
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# Clockevents broadcasting infrastructure
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config GENERIC_CLOCKEVENTS_BROADCAST
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bool
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depends on GENERIC_CLOCKEVENTS
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# Automatically adjust the min. reprogramming time for
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# clock event device
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config GENERIC_CLOCKEVENTS_MIN_ADJUST
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bool
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# Generic update of CMOS clock
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config GENERIC_CMOS_UPDATE
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bool
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if GENERIC_CLOCKEVENTS
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menu "Timers subsystem"
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# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
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# only related to the tick functionality. Oneshot clockevent devices
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# are supported independ of this.
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config TICK_ONESHOT
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bool
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config NO_HZ_COMMON
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bool
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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select TICK_ONESHOT
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choice
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prompt "Timer tick handling"
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default NO_HZ_IDLE if NO_HZ
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config HZ_PERIODIC
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bool "Periodic timer ticks (constant rate, no dynticks)"
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help
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This option keeps the tick running periodically at a constant
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rate, even when the CPU doesn't need it.
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config NO_HZ_IDLE
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bool "Idle dynticks system (tickless idle)"
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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select NO_HZ_COMMON
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help
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This option enables a tickless idle system: timer interrupts
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will only trigger on an as-needed basis when the system is idle.
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This is usually interesting for energy saving.
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Most of the time you want to say Y here.
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config NO_HZ_FULL
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bool "Full dynticks system (tickless)"
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# NO_HZ_COMMON dependency
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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# We need at least one periodic CPU for timekeeping
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depends on SMP
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# RCU_USER_QS dependency
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depends on HAVE_CONTEXT_TRACKING
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# VIRT_CPU_ACCOUNTING_GEN dependency
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depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
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select NO_HZ_COMMON
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select RCU_USER_QS
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select RCU_NOCB_CPU
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select VIRT_CPU_ACCOUNTING_GEN
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select IRQ_WORK
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help
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Adaptively try to shutdown the tick whenever possible, even when
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the CPU is running tasks. Typically this requires running a single
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task on the CPU. Chances for running tickless are maximized when
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the task mostly runs in userspace and has few kernel activity.
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You need to fill up the nohz_full boot parameter with the
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desired range of dynticks CPUs.
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This is implemented at the expense of some overhead in user <-> kernel
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transitions: syscalls, exceptions and interrupts. Even when it's
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dynamically off.
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Say N.
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endchoice
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config NO_HZ_FULL_ALL
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bool "Full dynticks system on all CPUs by default (except CPU 0)"
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depends on NO_HZ_FULL
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help
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If the user doesn't pass the nohz_full boot option to
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define the range of full dynticks CPUs, consider that all
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CPUs in the system are full dynticks by default.
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Note the boot CPU will still be kept outside the range to
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handle the timekeeping duty.
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config NO_HZ_FULL_SYSIDLE
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bool "Detect full-system idle state for full dynticks system"
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depends on NO_HZ_FULL
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default n
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help
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At least one CPU must keep the scheduling-clock tick running for
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timekeeping purposes whenever there is a non-idle CPU, where
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"non-idle" also includes dynticks CPUs as long as they are
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running non-idle tasks. Because the underlying adaptive-tick
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support cannot distinguish between all CPUs being idle and
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all CPUs each running a single task in dynticks mode, the
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underlying support simply ensures that there is always a CPU
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handling the scheduling-clock tick, whether or not all CPUs
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are idle. This Kconfig option enables scalable detection of
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the all-CPUs-idle state, thus allowing the scheduling-clock
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tick to be disabled when all CPUs are idle. Note that scalable
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detection of the all-CPUs-idle state means that larger systems
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will be slower to declare the all-CPUs-idle state.
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Say Y if you would like to help debug all-CPUs-idle detection.
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Say N if you are unsure.
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config NO_HZ_FULL_SYSIDLE_SMALL
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int "Number of CPUs above which large-system approach is used"
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depends on NO_HZ_FULL_SYSIDLE
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range 1 NR_CPUS
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default 8
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help
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The full-system idle detection mechanism takes a lazy approach
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on large systems, as is required to attain decent scalability.
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However, on smaller systems, scalability is not anywhere near as
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large a concern as is energy efficiency. The sysidle subsystem
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therefore uses a fast but non-scalable algorithm for small
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systems and a lazier but scalable algorithm for large systems.
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This Kconfig parameter defines the number of CPUs in the largest
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system that will be considered to be "small".
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The default value will be fine in most cases. Battery-powered
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systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
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numbers of CPUs, and (3) are suffering from battery-lifetime
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problems due to long sysidle latencies might wish to experiment
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with larger values for this Kconfig parameter. On the other
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hand, they might be even better served by disabling NO_HZ_FULL
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entirely, given that NO_HZ_FULL is intended for HPC and
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real-time workloads that at present do not tend to be run on
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battery-powered systems.
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Take the default if you are unsure.
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config NO_HZ
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bool "Old Idle dynticks config"
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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help
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This is the old config entry that enables dynticks idle.
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We keep it around for a little while to enforce backward
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compatibility with older config files.
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config HIGH_RES_TIMERS
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bool "High Resolution Timer Support"
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depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
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select TICK_ONESHOT
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help
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This option enables high resolution timer support. If your
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hardware is not capable then this option only increases
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the size of the kernel image.
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endmenu
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endif
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