linux-kernel - Re: CPU Hotplugging disabled, still cpuhp/%d threads running in my 32-bit system

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Message-ID: <alpine.DEB.2.20.1701111011210.3579@nanos>
Date:   Wed, 11 Jan 2017 10:16:10 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Enrico Mioso <mrkiko.rs@...il.com>
cc:     linux-kernel@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Peter Zijlstra <peterz@...radead.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: CPU Hotplugging disabled, still cpuhp/%d threads running in my
 32-bit system

On Tue, 10 Jan 2017, Enrico Mioso wrote:

> Hello guys.
> I disabled CPU hotplugging in my .config: still I can see what follows in the
> process list.
> 
>    11 ?        S      0:00 [cpuhp/0]
>    12 ?        S      0:00 [cpuhp/1]
> 
> And from what I can see in kernel/cpu.c:574, this is related to CPU
> hotplugging.
> Is this normal? And, out of curiosity, why?

Yes. We need the threads for bringing up the CPUs and for modules and other
functionality to set up per cpu related things. The thread makes sure that
the code runs on the CPUs and handles the functionality related to
install/remove of hotplug callbacks.

Thanks,

	tglx