diff options
| author | Andrew Morton <akpm@linux-foundation.org> | 2013-11-15 14:15:33 -0800 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2013-11-19 14:59:50 +0100 |
| commit | 050ded1bbaea3331745cf2782315f5bc2582d083 (patch) | |
| tree | 0d7005962a2611c254cec27736cb5750bea2b58c /kernel/time | |
| parent | da554eba2e68c8ec051977db5ee1f42d384a01ed (diff) | |
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>
Diffstat (limited to 'kernel/time')
| -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 64522ecdfe0e..162b03ab0ad2 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; /* |