linux-kernel - Re: [PATCH RFC] x86/acpi: don't ignore I/O APICs just because there's no local APIC

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Message-ID: <m1zlc5jqac.fsf@fess.ebiederm.org>
Date:	Thu, 18 Jun 2009 12:27:39 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Len Brown <lenb@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH RFC] x86/acpi: don't ignore I/O APICs just because there's no local APIC

Jeremy Fitzhardinge <jeremy@...p.org> writes:

> On 06/18/09 09:08, Len Brown wrote:
>>> In principle, the local APIC and the I/O APIC are distinct (but related)
>>> components, which can be independently present.
>>>     
>>
>> bzzzzt, but thanks for playing:-)
>>   
>
> Perhaps I should have expressed that a bit more clearly:  you could, if
> mad, build a machine with I/O APICs and some other mechanism for
> delivering the interrupts to CPUs.  In practice, I doubt anyone ever
> has, or ever would.
>
> The only actual exception I know of is Xen's replacement of the physical
> local APIC with a paravirtualized interrupt interface.

No one ever has.  Xen doesn't have I/O APICs either.  Not in any real
sense.  Xen just has devices that looking like I/O apics if you don't
look close.

Eric

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