Re: Max CPUs on x86_64 under 2.6.x

[William Lee Irwin III]

"Colin Coe" <colin@xxxxxxxxxx> 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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