From: Valentin Schneider <valentin.schneider@arm.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
tglx@linutronix.de, bristot@redhat.com, yejune.deng@gmail.com
Subject: Re: [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread
Date: Tue, 11 May 2021 10:33:08 +0100 [thread overview]
Message-ID: <871rad399n.mognet@arm.com> (raw)
In-Reply-To: <YJozF+wmiMYuSa6/@gmail.com>
On 11/05/21 09:32, Ingo Molnar wrote:
> * Valentin Schneider <valentin.schneider@arm.com> wrote:
>> 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. :-)
>
Well I got something that seems to work, let me it test it some more and
convince myself it isn't completely bonkers and I'll toss it out.
> Thanks,
>
> Ingo
next prev parent reply other threads:[~2021-05-11 9:33 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-10 15:10 [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Valentin Schneider
2021-05-10 15:10 ` [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Valentin Schneider
2021-05-10 15:57 ` Valentin Schneider
2021-05-11 7:32 ` Ingo Molnar
2021-05-11 9:33 ` Valentin Schneider [this message]
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2021-05-10 15:10 ` [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed Valentin Schneider
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Yejune Deng
2021-05-19 9:02 ` tip-bot2 for Yejune Deng
2021-05-31 10:21 ` [PATCH] sched,init: Fix DEBUG_PREEMPT vs early boot Peter Zijlstra
2021-06-01 11:54 ` Valentin Schneider
2021-06-01 14:04 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-05-12 11:00 ` [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Peter Zijlstra
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