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

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Message-ID: <alpine.LNX.2.20.1701111408230.7486@localhost.localdomain>
Date:   Wed, 11 Jan 2017 14:08:49 +0100 (CET)
From:   Enrico Mioso <mrkiko.rs@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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

Thank you very much Thomas, really.
Enrico


Enrico Mioso
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On Wed, 11 Jan 2017, Thomas Gleixner wrote:

> Date: Wed, 11 Jan 2017 10:16:10
> 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
>