Date: Mon, 3 Jan 2005 18:20:34 -0800
From: William Lee Irwin III <wli@holomorphy.com>
To: Andi Kleen <ak@muc.de>
Cc: colin@coesta.com, linux-kernel@vger.kernel.org
Subject: Re: Max CPUs on x86_64 under 2.6.x
Message-ID: <20050104022034.GB2708@holomorphy.com>
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"Colin Coe" <colin@coesta.com> writes:
>> Why is the number of CPUs on the x86_64 architecture only 8 but under i386
>> it is 255?
>> I've searched the list archives and Google but can't find an answer.

On Tue, Jan 04, 2005 at 01:34:50AM +0100, Andi Kleen wrote:
> Post 2.6.10 x86-64 will support more CPUs. 2.6.10 actually does too,
> but the Kconfig hadn't been changed then. Previously there was an
> 8 CPU APIC driver limit, however it turned out later that it doesn't
> apply to some Opteron machines.

Barring cpus with a different onboard interrupt controller from the
xAPIC or the use of external interrupt controllers to assist with cpu
addressing, 255 serves as an architectural limit for Opteron as well.


-- wli
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