linux-kernel - maxcpus confusion

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Message-ID: <e56b3c83-1488-e104-0d1d-f21f8c0116b1@infradead.org>
Date:   Fri, 1 Dec 2017 12:58:47 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     X86 ML <x86@...nel.org>
Subject: maxcpus confusion

Hi,

I used "maxcpus=1" on a recent x86 boot (4.15-rc1) and got 4 CPUs (all of
them AFAICT).  When I use "nr_cpus=1", I do get a hard limit of one CPU.


A few boot log excerpts:

[    0.000000] smpboot: Allowing 8 CPUs, 4 hotplug CPUs
...
[    0.030007] smp: Bringing up secondary CPUs ...
[    0.030109] smp: Brought up 1 node, 1 CPU
[    0.030181] smpboot: Max logical packages: 4
[    0.030255] smpboot: Total of 1 processors activated (4789.06 BogoMIPS)


Is systemd (or something else) later onlining the other CPUs?

/sys/devices/system/cpu/online is 0-3
/sys/devices/system/cpu/offline is 4-7


Full boot log is attached.


thanks.
-- 
~Randy

View attachment "log-maxcpus1.out" of type "text/plain" (168293 bytes)