Hi Viresh and Thomas,
In the functions tick_nohz_stop_sched_tick(), when expires = KTIME_MAX
we are canceling the tick_sched_timer timer but we are not updating the
clock event device’s next_event to KTIME_MAX.
Due to that broadcast device’s next_event is not programmed properly and
resulting unnecessary wakeups for this cpu.
/*
* If the expiration time == KTIME_MAX, then we simply stop
* the tick timer.
*/
if (unlikely(expires == KTIME_MAX)) {
if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
hrtimer_cancel(&ts->sched_timer);
goto out;
}
After digging further, I see that following call flow is updating
tick_cpu_device state to shutdown state but clock event device
next_event is not updated to KTIME_MAX.
hrtimer_cancel -> __remove_hrtimer -> hrtimer_force_reprogram ->
tick_program_event.
int tick_program_event(ktime_t expires, int force)
{
struct clock_event_device *dev =
__this_cpu_read(tick_cpu_device.evtdev);
if (unlikely(expires == KTIME_MAX)) {
/*
* We don't need the clock event device any more, stop
it.
*/
clockevents_switch_state(dev,
CLOCK_EVT_STATE_ONESHOT_STOPPED);
return 0;
}
In the above tick_program_event() function clock event device’s
next_event is not getting updated as clockevents_program_event()
function not called after state update.
-thanks, Prasad
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