Messages in this thread | | | Date | Mon, 23 Oct 2017 21:33:09 -0700 | From | Sodagudi Prasad <> | Subject | clock event device’s next event |
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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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