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SubjectRe: [Query]: tick-sched: why don't we stop tick when we are running idle task?
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On 10 April 2014 20:09, Frederic Weisbecker <fweisbec@gmail.com> wrote:
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 9f8af69..1e2d6b7 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -202,13 +202,16 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
> void __tick_nohz_full_check(void)
> {
> struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
> + unsigned long flags;
>
> + local_irq_save(flags);

As we need to disable interrupts to read this variable, would it be
better to just remove this completely and use is_idle_task(current)
instead?

> if (tick_nohz_full_cpu(smp_processor_id())) {
> - if (ts->tick_stopped && !is_idle_task(current)) {
> + if (ts->tick_stopped && !ts->inidle)) {
> if (!can_stop_full_tick())
> tick_nohz_restart_sched_tick(ts, ktime_get());
> }
> }
> + local_irq_restore(flags);
> }

> If you like it I'll push it to Ingo.

Yes please. And thanks for the explanations. It was pretty useful.

I am looking to offload 1 second tick to timekeeping CPUs and so
going through these frameworks. I don't have a working solution yet
(even partially :)). Would send a RFC to you as soon as I get anything
working.

--
viresh


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