linux-kernel - Re: the maxcpus= boot parameter broke somewhere along the line

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Message-ID: <x49sjgmgpwc.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 02 Apr 2012 10:38:27 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	Nick Bowler <nbowler@...iptictech.com>,
	linux-kernel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>
Subject: Re: the maxcpus= boot parameter broke somewhere along the line

"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> writes:

> On 04/02/2012 07:35 PM, Jeff Moyer wrote:
>
>> "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> writes:
>> 
>>> Looking at the mention of udev above, and considering the commit you bisected
>>> to, I think it would be good to see whether someone is writing 1 to
>>> /sys/device/system/cpu/cpu*/online and hence the cpus are getting hot-added
>>> towards the end of boot. Maybe that sounds stupid, but worth a try :)
>>>
>>> So can you try the debug patch below? It applies on latest linux-3.3-rc6+
>> 
>> Sorry it took me so long to get back to you.  You're patch did, in fact,
>> trigger:
>> 
>> udev: starting version 147
>> CPU 3 online initated from userspace
>> SMP alternatives: switching to SMP code
>> WARNING! power/level is deprecated; use power/control instead
>> Booting Node 0 Processor 3 APIC 0x3
>> NMI watchdog: enabled, takes one hw-pmu counter.
>> CPU 1 online initated from userspace
>> Booting Node 0 Processor 1 APIC 0x2
>> NMI watchdog: enabled, takes one hw-pmu counter.
>> CPU 2 online initated from userspace
>> Booting Node 0 Processor 2 APIC 0x1
>> NMI watchdog: enabled, takes one hw-pmu counter.
>> CPU 1 online initated from userspace
>> CPU 3 online initated from userspace
>> CPU 2 online initated from userspace
>> 
>
>
> Aha! Just like I thought!
> So there is no kernel bug with respect to the maxcpus= boot parameter :-)

But this IS a change in behaviour (using older kernels, the maxcpus=
boot parameter works just fine).  So, what exactly has changed is my
question, and what is the right way to fix it?

Cheers,
Jeff
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