Re: [Xen-ia64-devel] vIOSAPIC and IRQs delivery

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Jeudi 09 Mars 2006 11:13, Kenji Kaneshige a écrit :
> Hi,
>
> Tristan Gingold wrote:
> > Le Jeudi 09 Mars 2006 01:31, Luck, Tony a écrit :
> >>>BTW, I think it will be *very* hard to find an ia64 platform which can
> >>>share an IRQ line.  Maybe I am wrong but I don't know such a platform
> >>> :-(
> >>
> >>Hard? No.
> >
> > I'd like to have a vendor name and a platform name!
>
> Fujitsu PRIMEQUEST can have so many (> 512) gsi sources and it
> needs shared IRQ (vector). Note that what I'm talking is not
> sharing IRQ lines but sharing interrupt vector between multiple
> RTEs.
Ok this is interesting.
So, you don't share IRQ lines.  My question still stands!
Sharing vectors is easier, since we should assign one vector to one machine 
for optimization.  We don't want to deliver useless interrupts.

> >>Expensive? Yes.
> >>
> >>There are only 255 irqs - minus some that the base kernel steals
> >>for cmc, mca, timer, perfmon, etc.  So any large system with a
> >>few hundred i/o cards _must_ share irqs.  There aren't enough
> >>for one each.
> >
> > I don't agree.  You can have interrupt domains.  See "Intel Itanium
> > Processor Family Interrupt Architecture Guide".
>
> As you said, interrupt domains approach is better because
>
>     - Shared IRQ (vector) approach would not work for
>       edge-triggered interrupts including MSIs.
>
>     - Interrupt domains approach would have much better
>       performance
>
> Unfortunately, AFAIK, interrupt domains approach has not be
> implemented for generic ia64-linux kernel yet. It would be
> very nice if it is implemented someday. But I guess we need
> a lot of efforts for it. To tell the truth, I've posted the
> patches for interrupt domains to ia64-linux mailing list
> before, though it contains many TBDs and bugs (maybe).
Ok.
Maybe it can be more easily done in Xen ?

Tristan.


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