>From: Ingo Molnar <[EMAIL PROTECTED]>
>On Sat, 27 Nov 1999, Aaron Tiensivu wrote:
>
>> I've wondered this a while and it seems like it would make sense for
>> Uni-processor boards to use an IO-APIC also. Lots of people have had
>> trouble with sharing IRQs/etc and IO-APIC is a lot more elegant than
>> the age old XT pic on most boards. Is it just a matter of cost? Does
>> Intel's IO-APIC chip carry a cost they don't want to carry?
>
>i guess part of the picture is cost, but also the fact that 1) Windows
>doesnt use the IOAPIC at all 2) NT uses it only in SMP mode, just like
>Linux. Why build hardware at a higher cost that no OS supports?
You are mistaken about NT.
NT 4.0 (and probably Windows 2000) uses IOAPIC HAL with
the UP kernel on a dual board with a single CPU.
BeOS uses IOAPIC on dual boards by default, regardless on the number
of the installed CPUs.
>
>> Personally, I think I'd buy a uni-box with an IO-APIC, it would
>> certainly help bang out some bugs because SMP boxes are still somewhat
>> rare.
>
>as far as the kernel goes: i did the related changes to decouple the
>IOAPIC from SMP about a year ago already - some of the SGI VisWS boxes
>were UP but used an IOAPIC.
>
>i believe it should work already: enable the CONFIG_IOAPIC line in your
>.config - it should compile and boot i believe.
>
>(there is one case where it's useful and it was mentioned here some time
>ago: dual board with a single CPU running UP kernel with IOAPIC
>interrupts.)
>
All new Intel chipsets (i820 and i840) have the IOAPIC in the common IO hub,
so _all_ i820 & i840 MBs have IOAPIC, MBs with i840 will have 2 IOAPICs
if they have 2 PCI busses. Unfortunatly, BIOSes on UP MBs don't build
the SMP table so the current versions of Linux and BeOS can't use IOAPIC on
such boards.
Dmitriy Budko [EMAIL PROTECTED]
Be Incorporated http://www.be.com
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