On Sat, 24 Dec 2016, Frederic Weisbecker wrote:
> static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
> ktime_t now, int cpu)
> {
> - struct clock_event_device *dev =
> __this_cpu_read(tick_cpu_device.evtdev);
> u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
> unsigned long seq, basejiff;
> ktime_t tick;
> @@ -767,7 +766,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct
> tick_sched *ts,
> tick.tv64 = expires;
>
> /* Skip reprogram of event if its not changed */
> - if (ts->tick_stopped && (expires == dev->next_event.tv64))
> + if (ts->tick_stopped && (expires == ts->next_tick.tv64))
> goto out;
Good catch!
>
> /*
> @@ -787,6 +786,8 @@ static ktime_t tick_nohz_stop_sched_tick(struct
> tick_sched *ts,
> trace_tick_stop(1, TICK_DEP_MASK_NONE);
> }
>
> + ts->next_tick = tick;
> +
> /*
> * If the expiration time == KTIME_MAX, then we simply stop
> * the tick timer.
> @@ -803,7 +804,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct
> tick_sched *ts,
> tick_program_event(tick, 1);
> out:
> /* Update the estimated sleep length */
> - ts->sleep_length = ktime_sub(dev->next_event, now);
> + ts->sleep_length = ktime_sub(ts->next_tick, now);
This is wrong. If the next event is earlier than the next estimated tick
then tick_nohz_get_sleep_length() will return crap and the idle governor
will go into a deeper C-state than sensible.
Thanks,
tglx
