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

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Date:   Wed, 21 Mar 2018 10:41:21 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Dou Liyang <douly.fnst@...fujitsu.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-acpi@...r.kernel.org, linux-doc@...r.kernel.org,
        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, 21 Mar 2018, 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
> 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 limits the number of CPUs the kernel will handle. Think of it as a
boot time override of NR_CPUs.

Way too many commandline switches though.

Thanks,

	tglx