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Date: Sun, 5 Jul 2009 23:46:08 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: "H. Peter Anvin" <hpa@zytor.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
Message-ID: <20090705194608.GL4791@lenovo>
References: <20090705162044.GC4791@lenovo> <alpine.LFD.2.00.0907051737100.13862@eddie.linux-mips.org> <4A50E323.6060109@zytor.com> <20090705190211.GK4791@lenovo> <4A50FC68.1030002@zytor.com>
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[H. Peter Anvin - Sun, Jul 05, 2009 at 12:18:00PM -0700]
| 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
| 

Then this patch (eventually) should be dropped. I need to re-check
all this.

	-- Cyrill