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

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Message-ID: <4F79B891.8020704@linux.vnet.ibm.com>
Date:	Mon, 02 Apr 2012 20:02:49 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Jeff Moyer <jmoyer@...hat.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

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 :-)
 
Regards,
Srivatsa S. Bhat

> Checking through udev rules, I found this in
> /lib/udev/rules.d/40-redhat.rules (this is a RHEL 6 install, btw):
> 
> ACTION=="add", KERNEL=="cpu[0-9]*", RUN+="/bin/bash -c 'echo 1 > /sys/devices/system/cpu/%k/online'"
> 
> So, what do you suppose is the right way to fix this?
> 
> Cheers,
> Jeff
> 
> Kay, you can read up on the rest of the thread here:
> https://lkml.org/lkml/2012/3/6/242
> 


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