Re: [Query]: tick-sched: why don't we stop tick when we are running idle task?

[Viresh Kumar]

On 9 April 2014 16:03, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> Hi Frederic,
>
> File: kernel/time/tick-sched.c
> Function: tick_nohz_full_stop_tick()
>
> We are doing this:
>
> if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
>         return;
>
> Which means: if a FULL_NO_HZ cpu is running idle task currently,
> don't stop its tick..
>
> I couldn't understand why. Can you please help here?

Is it because of this code ? :

void tick_nohz_irq_exit(void)
{
        struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

        if (ts->inidle)
                __tick_nohz_idle_enter(ts);
        else
                tick_nohz_full_stop_tick(ts);
}

i.e. tick_nohz_full_stop_tick() would never be called while we have
'inidle' set or we are running idle task?

In this case as well, we don't really need that check to be present.
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