linux-kernel - Re: [RFC -tip] x86,apic -- reduce disable

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Date:	Sun, 5 Jul 2009 23:46:08 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <yinghai@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] x86,apic -- reduce disable_apic usage

[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
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