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Almost all machines use GENERIC_CLOCKEVENTS, so it feels wrong to require each one to select that symbol manually. Instead, enable it whenever CONFIG_LEGACY_TIMER_TICK is disabled as a simplification. It should be possible to select both GENERIC_CLOCKEVENTS and LEGACY_TIMER_TICK from an architecture now and decide at runtime between the two. For the clockevents arch-support.txt file, this means that additional architectures are marked as TODO when they have at least one machine that still uses LEGACY_TIMER_TICK, rather than being marked 'ok' when at least one machine has been converted. This means that both m68k and arm (for riscpc) revert to TODO. At this point, we could just always enable CONFIG_GENERIC_CLOCKEVENTS rather than leaving it off when not needed. I built an m68k defconfig kernel (using gcc-10.1.0) and found that this would add around 5.5KB in kernel image size: text data bss dec hex filename 3861936 1092236 196656 5150828 4e986c obj-m68k/vmlinux-no-clockevent 3866201 1093832 196184 5156217 4ead79 obj-m68k/vmlinux-clockevent On Arm (MACH_RPC), that difference appears to be twice as large, around 11KB on top of an 6MB vmlinux. Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Tested-by: Geert Uytterhoeven <geert@linux-m68k.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
176 lines
4.8 KiB
Plaintext
176 lines
4.8 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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#
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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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# Architecture has extra clocksource init called from registration
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config ARCH_CLOCKSOURCE_INIT
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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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# The generic clock events infrastructure
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config GENERIC_CLOCKEVENTS
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def_bool !LEGACY_TIMER_TICK
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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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# Select to handle posix CPU timers from task_work
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# and not from the timer interrupt context
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config HAVE_POSIX_CPU_TIMERS_TASK_WORK
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bool
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config POSIX_CPU_TIMERS_TASK_WORK
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bool
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default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
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config LEGACY_TIMER_TICK
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bool
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help
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The legacy timer tick helper is used by platforms that
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lack support for the generic clockevent framework.
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New platforms should use generic clockevents instead.
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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 independent 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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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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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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# We need at least one periodic CPU for timekeeping
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depends on SMP
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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_NOCB_CPU
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select VIRT_CPU_ACCOUNTING_GEN
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select IRQ_WORK
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select CPU_ISOLATION
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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 CONTEXT_TRACKING
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bool
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config CONTEXT_TRACKING_FORCE
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bool "Force context tracking"
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depends on CONTEXT_TRACKING
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default y if !NO_HZ_FULL
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help
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The major pre-requirement for full dynticks to work is to
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support the context tracking subsystem. But there are also
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other dependencies to provide in order to make the full
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dynticks working.
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This option stands for testing when an arch implements the
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context tracking backend but doesn't yet fullfill all the
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requirements to make the full dynticks feature working.
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Without the full dynticks, there is no way to test the support
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for context tracking and the subsystems that rely on it: RCU
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userspace extended quiescent state and tickless cputime
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accounting. This option copes with the absence of the full
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dynticks subsystem by forcing the context tracking on all
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CPUs in the system.
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Say Y only if you're working on the development of an
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architecture backend for the context tracking.
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Say N otherwise, this option brings an overhead that you
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don't want in production.
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config NO_HZ
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bool "Old Idle dynticks config"
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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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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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