RE: [Xen-devel] [PATCH] x86: change IO-APIC ack method default for single IO-APIC systems

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx <> wrote:
> On 21/01/2009 14:21, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
> 
>> "ioapic_ack=old". With that knowledge I think it is now reasonable to
>> include that patch in -unstable, as the introduction of the 'new' ack
>> method was only to address issues with certain chipsets silently
>> setting up alternative IRQ routes when RTEs in secondary IO-APICs got
>> masked.
> 
> I don't specifically recall that this issue required two
> IO-APICs. In fact I
> think it did not. It was actually something to do with the
> chipset trying to
> distinguish between an OS using 'legacy' routing versus 'mp-bios' routing,
> via a rather distasteful IO-APIC hack. Unfortunately the hack
> was not that
> uncommon and I don't think those chipsets had more than one IO-APIC.

I remember there are two IO-APICs, the second one is in a PXH hub, not in the 
chipset. and it is this external IOAPIC will do something tricky as Jan 
described. It is really a very old story and maybe I'm wrong.

> 
> Overall I think ack_type new has worked quite well. I was
> actually about to
> remove the old ack_type! (But now I won't ;-) I'm not inclined
> to take this
> patch though.
> 
> -- Keir
> 
> 
> 
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