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

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Message-ID: <20111206135246.GC30018@elte.hu>
Date:	Tue, 6 Dec 2011 14:52:46 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Borislav Petkov <bp@...64.org>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	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>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>
Subject: Re: [PATCH v4 0/7] x86: BSP or CPU0 online/offline


* Borislav Petkov <bp@...64.org> wrote:

> On Tue, Dec 06, 2011 at 04:55:02PM +0530, Srivatsa S. Bhat wrote:
>
> > 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).
> 
> Just a reminder: before you guys go and wander off into the 
> woods of hypothetical with this, please make sure this use 
> case is relevant enough for the trouble. The only real reason 
> given so far AFAICT was RAS and to be able to offline BSP in 
> order to prolong system life before maintenance.
> 
> When you take it down for maintenance eventually, you don't 
> need to suspend but simply poweroff.

I think it's definitely a marginal and speculative feature - but 
the patches don't look overly complicated, so i'm not 
*completely* against removing various boot-CPU assumptions 
(although i'm predisposed against it) - if it is correct and if 
there's someone interested in doing proper patches.

All in one, the quality threshold for inclusion is very high but 
not an infinite number.

The specific point i tried to make about s2ram is to make sure 
it does not break during normal usage: for example someone 
offlines the boot CPU, but the box then gets suspended - that 
should not hang or crash.

Thanks,

	Ingo
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