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

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Message-ID: <20180321090826.GW4043@hirez.programming.kicks-ass.net>
Date:   Wed, 21 Mar 2018 10:08:26 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
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

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
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.