Date: Sun, 14 Sep 1997 14:46:24 +0800 From: Peter Wemm <peter@spinner.dialix.com.au> To: Terry Lambert <tlambert@primenet.com> Cc: missmanp@milo.cfw.com (Paul Missman), freebsd-smp@freebsd.org Subject: Re: SMP in FreeBSD 3.x.x Message-ID: <199709140646.OAA22630@spinner.dialix.com.au> In-Reply-To: Your message of "Sun, 14 Sep 1997 04:24:08 GMT." <199709140424.VAA07740@usr08.primenet.com>
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Terry Lambert wrote:
> > I see that the SMP source was merged with the 3.x.x development kernal.
> > Does this mean that 3.x.x, when released, will seamlessly support 1 - N
> > processors? Also, what do you imagine maximum N will be at 3.x.x release
> > time? I believe the original Intel spec was up to 4 processors, but I see
a
> > lot of 8 processor servers coming out lately.
>
> A system can have up to 32 APICs. It is the APIC IDs that limit
> the number of processors.
>
> Given that a system will have an I/O APIC, the max is 31 (except
> for I2O systems, where the i960 also has an APIC, or systems with
> multiple bus controllers -- each with an APIC).
>
> So ~30.
No, the APIC id's go from 0 to 15, and if memory serves, "15" is used as
an 'all processors' value in some places.. The limit is either 15 or 16
APIC device id's depending on that. Since there should be at least one IO
APIC (or there's not much point doing SMP), that makes the limit either 14
or 15 cpus. This is for a conventional APIC bus structure of course. :-)
The MPSPEC (or was it the pentium family hardware docs?) talks about APIC
bridges and wild things like that which could (I think) take the device
limit up higher (60 devices seems to ring a bell), but it's the least of
our worries at the moment. :-)
The older 82489DX i486 APIC had an 8-bit device ID and a 4-wire APIC bus
(the p5/p6 family have a 2-wire bus with 4-bit id's).
A non-intel system such as OpenPIC would have different constraints,
assuming the hardware actually exists.
> Terry Lambert
> terry@lambert.org
> ---
> Any opinions in this posting are my own and not those of my present
> or previous employers.
>
Cheers,
-Peter
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