linux-kernel - Re: [PATCH v4 0/7] x86: BSP or CPU0 online/offline

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Message-ID: <4EDDF2DE.7020701@linux.vnet.ibm.com>
Date:	Tue, 06 Dec 2011 16:17:58 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Fenghua Yu <fenghua.yu@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Len Brown <len.brown@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>,
	Tejun Heo <tj@...nel.org>, Borislav Petkov <bp@...64.org>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>
Subject: Re: [PATCH v4 0/7] x86: BSP or CPU0 online/offline

On 12/06/2011 04:05 PM, Ingo Molnar wrote:

> 
> * Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> 
>>> But the hibernation angle should be considered. Hibernation 
>>> already has to deal with the case where someone physically 
>>> unplugs a CPU and then resumes from the disk image, right? 
>>> How does the hibernation code handle that case currently?
>>
>> Oh, wait a minute. Are we talking about physical CPU Hotplug 
>> in between hibernation and restore? AFAIK, currently we don't 
>> handle that at all. [...]
> 
> Well, not hotplug, but plain old-fashioned: 'hibernate the box, 
> take out a CPU physically and thaw' kind of hardware change.
>


Well, actually that's what I meant, taking this same idea a bit
further: hibernate the box, take out a CPU physically, insert a
slightly different CPU (which needs a different microcode image)
and thaw.

In this case, the other patch that I mentioned in my previous mail
would be required (or an equivalent), because the optimization
patch which is now in mainline, would apply the same old microcode
image on this new CPU too, blindly.

 
> How will the hibernation code handle this case?


I am not familiar with how the rest of the hibernation code handles
the case you described. I just happen to know about the microcode
case needing some more work for this to work reliably.

Regards,
Srivatsa S. Bhat
IBM Linux Technology Center

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