linux-kernel - Re: [PATCH 1/5] x86/smpboot: Add the missing description of possible

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Date:   Wed, 21 Mar 2018 17:34:12 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <linux-acpi@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <corbet@....net>,
        <rjw@...ysocki.net>, <lenb@...nel.org>, <hpa@...or.com>
Subject: Re: [PATCH 1/5] x86/smpboot: Add the missing description of
 possible_cpus

Hi Peter,

At 03/21/2018 05:08 PM, Peter Zijlstra wrote:
> On Wed, Mar 21, 2018 at 01:33:24PM +0800, Dou Liyang wrote:
>> How about:
>>
>> possible_cpus=	[s390,x86_64] Set the number of possible CPUs which
>> 		are determined by the ACPI tables MADT or mptables by
>> 		default. possible_cpus=n : n >= 1 enforces the possible
>> 		number to be 'n'.
>> 		While nr_cpus is also be set: nr_cpus=m, choice the
>> 		minimum one for the number of possible CPUs.
> 
> So what is the exact difference between possible_cpus and nr_cpus ? I

the possible_cpus= can reset the number of possible CPUs, even bigger
than 'num_processors + disabled_cpus', But nr_cpus= can't.

> konw maxcpus= limits the number of CPUs we bring up, and possible_cpus
> limits the possible_map, but I'm not entirely sure what nr_cpus does
> here.
> 

nr_cpus can limited the maximum CPUs that the kernel could support.

Here is a double check in case of using them at the same time, even if I
think just using possible_cpus= is enough. :-)

Thanks,
	dou.
> 
>