diff options
| author | Andrew Morton <akpm@linux-foundation.org> | 2013-11-05 16:54:55 +1100 |
|---|---|---|
| committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2013-11-05 16:54:55 +1100 |
| commit | 69d585c225fe6dd456278703d06eb746a370cab1 (patch) | |
| tree | 4d2c1929eb74b56c2e4065ae4d3d6d9cc248f884 /kernel | |
| parent | e29a1deed5a387889eaf1f2311c243c67d67b24f (diff) | |
kernel/time/tick-common.c: document tick_do_timer_cpu
Taken straight from a tglx email ;)
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'kernel')
| -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; /* |