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SubjectRe: [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread

* Valentin Schneider <valentin.schneider@arm.com> wrote:

> On 10/05/21 16:10, Valentin Schneider wrote:
> > This requires some extra iffery as init_idle()
> > call be called more than once on the same idle task.
> >
>
> While I'm at it, do we actually still need to suffer through this?

No.

> AFAICT the extra calls are due to idle_thread_get() (used in cpuhp)
> calling init_idle(). However it looks to me that since
>
> 3bb5d2ee396a ("smp, idle: Allocate idle thread for each possible cpu during boot")
>
> we don't need to do that: we already have a
>
> for_each_possible_cpu(cpu)
> init_idle(cpu)
>
> issued at init. So can't we "simply" rely on that init-time creation,
> given it's done against the possible mask? I think the only thing that
> might need doing at later hotplug is making sure the preempt count is
> right (secondary startups seem to all prepare the idle task by issuing a
> preempt_disable()).

Best-case it works, worst-case we discover an unclean assumption in the
init sequence and it works after we fix that.

Win-win. :-)

Thanks,

Ingo

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