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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2013-12-04 08:52:09 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-12-04 08:52:09 -0800 |
| commit | 1ab231b274ba51a54acebec23c6aded0f3cdf54e (patch) | |
| tree | 2ce15cb4ba9adf3e041eb9d1b26f63292c953094 /kernel/time/tick-common.c | |
| parent | dea4f48a0a301b23c65af8e4fe8ccf360c272fbf (diff) | |
| parent | 0e576acbc1d9600cf2d9b4a141a2554639959d50 (diff) | |
Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer fixes from Thomas Gleixner:
- timekeeping: Cure a subtle drift issue on GENERIC_TIME_VSYSCALL_OLD
- nohz: Make CONFIG_NO_HZ=n and nohz=off command line option behave the
same way. Fixes a long standing load accounting wreckage.
- clocksource/ARM: Kconfig update to avoid ARM=n wreckage
- clocksource/ARM: Fixlets for the AT91 and SH clocksource/clockevents
- Trivial documentation update and kzalloc conversion from akpms pile
* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
nohz: Fix another inconsistency between CONFIG_NO_HZ=n and nohz=off
time: Fix 1ns/tick drift w/ GENERIC_TIME_VSYSCALL_OLD
clocksource: arm_arch_timer: Hide eventstream Kconfig on non-ARM
clocksource: sh_tmu: Add clk_prepare/unprepare support
clocksource: sh_tmu: Release clock when sh_tmu_register() fails
clocksource: sh_mtu2: Add clk_prepare/unprepare support
clocksource: sh_mtu2: Release clock when sh_mtu2_register() fails
ARM: at91: rm9200: switch back to clockevents_config_and_register
tick: Document tick_do_timer_cpu
timer: Convert kmalloc_node(...GFP_ZERO...) to kzalloc_node(...)
NOHZ: Check for nohz active instead of nohz enabled
Diffstat (limited to 'kernel/time/tick-common.c')
| -rw-r--r-- | kernel/time/tick-common.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 64522ecdfe0..162b03ab0ad 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -33,6 +33,21 @@ DEFINE_PER_CPU(struct tick_device, tick_cpu_device); */ ktime_t tick_next_period; ktime_t tick_period; + +/* + * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR + * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This + * variable has two functions: + * + * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the + * timekeeping lock all at once. Only the CPU which is assigned to do the + * update is handling it. + * + * 2) Hand off the duty in the NOHZ idle case by setting the value to + * TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks + * at it will take over and keep the time keeping alive. The handover + * procedure also covers cpu hotplug. + */ int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT; /* |