Commit 050ded1b authored by Andrew Morton's avatar Andrew Morton Committed by Thomas Gleixner
Browse files

tick: Document tick_do_timer_cpu 



Taken straight from a tglx email ;)

Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent da554eba

kernel/time/tick-common.c

+15 −0
Original line number Diff line number Diff line
@@ -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;



/*