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tick: Document tick_do_timer_cpu 

Taken straight from a tglx email ;)

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Andrew Morton 2013-11-15 14:15:33 -08:00 committed by Thomas Gleixner
parent da554eba2e
commit 050ded1bba
1 changed files with 15 additions and 0 deletions
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15
kernel/time/tick-common.c
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@ -33,6 +33,21 @@ DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
*/ */
ktime_t tick_next_period; ktime_t tick_next_period;
ktime_t tick_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; int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
/* /*