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

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Message-ID: <4EDDFB8E.10801@linux.vnet.ibm.com>
Date:	Tue, 06 Dec 2011 16:55:02 +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 04:17 PM, Srivatsa S. Bhat wrote:

> 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.
> 


By the way, this problem is not tied to CPU0 alone, it exists for any
CPU! (as long as we are talking about plugging in/out CPUs physically).

Regards,
Srivatsa S. Bhat

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