linux-kernel - Re: [PATCH v5 10/12] x86/mtrr/main.c: Ask the first online CPU to save mtrr

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Message-ID: <4F136A50.80203@zytor.com>
Date:	Sun, 15 Jan 2012 16:07:44 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Brian Gerst <brgerst@...il.com>
CC:	Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	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>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Chen Gong <gong.chen@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v5 10/12] x86/mtrr/main.c: Ask the first online CPU to
 save mtrr

On 01/12/2012 04:33 AM, Brian Gerst wrote:
> On Wed, Jan 11, 2012 at 12:04 PM, Fenghua Yu <fenghua.yu@...el.com> wrote:
>> From: Fenghua Yu <fenghua.yu@...el.com>
>>
>> Ask the first online CPU to save mtrr instead of asking BSP. BSP could be
>> offline when mtrr_save_state() is called.
> 
> If you can use any non-boot cpu to save the MTRRs why not just use the
> current cpu?  They should all be in sync anyways.
> 

A much bigger question: why do we ever bother saving the MTRR state per
se?  We examine the MTRR state -- we have to -- during boot, and it
should never diverge from the state set by the OS from that point on --
we'll need to set it back to that.  So we should just keep track of what
the correct MTRR state is at all times.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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