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SubjectRe: [PATCH -tip] x86: do_boot_cpu - check if we have ESR register
On Wed, 22 Oct 2008, Ingo Molnar wrote:

> ah, Compaq - how many CPUs does that box support? If it's 8 or more then
> perhaps they turned off the real local APIC, fudged some chipset glue to
> emulate APIC functionality and thus were able to use 8 or more of these
> chips? The built-in lapic would only go up to 4 CPUs. (or maybe even
> just up to dual, depending on the model)

Hmm, interesting. The integrated APIC should support up to 14 CPUs
(assuming one ID is needed for the I/O APIC). One cannot preclude silicon
errata affecting the less common hardware configurations though. It would
be interesting to see a full bootstrap log with all the APIC debug
information enabled. That would probably clarify matters a bit.

Note that Compaq would have to come with their own solution about the
discrete APIC as the 82489DX went out of production many years ago -- ten
at the very least. OTOH, they could have stockpiled them back then. ;)
This is one of the few manufacturers I would actually suspect doing so as
they always seemed keen on going SMP. Good to know we can support these
boxes at all these days.

> This reminds us that all the is-integrated-lapic checks still matter
> today.

Quite surprising indeed.


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