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Message-ID: <92645B27BF79D04FBD2B0F8494FFD0F91F2222@G1W3649.americas.hpqcorp.net>
Date: Wed, 19 Dec 2012 10:36:00 +0000
From: "Zhang, Lin-Bao (Linux Kernel R&D)" <linbao.zhang@...com>
To: Yinghai Lu <yinghai@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
"mingo@...hat.com" <mingo@...hat.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
"jarkko.sakkinen@...el.com" <jarkko.sakkinen@...el.com>,
"joerg.roedel@....com" <joerg.roedel@....com>,
"agordeev@...hat.com" <agordeev@...hat.com>
Subject: RE: Why Linux kernel forced to enter X2APIC mode( just because of
booting cpu has supported x2apic) without depending on BIOS' setting in
MSR->x2apic enablement bit ?
Hi Yinghai ,
Actually ,my question like this:
OS can really enable x2apic correctly without BIOS' help in this case :
BIOS has claimed definitely it doesn't enable x2apic ,but OS feel it can enable x2apic(based on BSP supports x2apic) ).
If Linux don't need BIOS' help , how did linux kernel reach this action?
I am reading this related code, I just see Linux kernel judge cpu_has_x2apic() ,if yes, it will set MSR, certainly , IR works right.
We can think BIOS' supporting is not necessary ?
Thanks very much .
-- Bob(LinBao Zhang)
HP linux kernel enginner
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