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Date: Sun, 05 Jul 2009 12:18:00 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Cyrill Gorcunov <gorcunov@gmail.com>
CC: "Maciej W. Rozycki" <macro@linux-mips.org>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>, Yinghai Lu <yinghai@kernel.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC -tip] x86,apic -- reduce disable_apic usage
References: <20090705162044.GC4791@lenovo> <alpine.LFD.2.00.0907051737100.13862@eddie.linux-mips.org> <4A50E323.6060109@zytor.com> <20090705190211.GK4791@lenovo>
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Cyrill Gorcunov wrote:
> 
> Peter, Maciej but how kernel behaved on older cpu long time ago?
> 
> I mean -- should user pass "lapic" cmdline option too be
> able to use apic functionality? (i'm asking since I just
> don't know how it had been working before). Current
> code (if only I'm not _missing_ something) relies on cpu_has_apic
> bit. And even if MP table has been parsed and APIC base found,
> cpu_has_apic could be not set so detect_init_APIC will fail
> if no "lapic" option passed (in case of old cpu without this cpuid
> bit produced) as we eventually stay with pic mode.
> 

Well, systems with discrete APICs were few and far between.  I'm not
sure if there are any such systems still in meaningful existence (kind
of like Voyager.)  That makes it a bit hard to test things, and
certainly means we shouldn't bend over backwards in doing *anything*
that could possibly break other machines.

	-hpa

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