number of interrupt sources limit

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

Hello,
actually, the number of interrupt sources per CPU (but all peripheral
interrupts are routed to the BSP) is limited to 32. Is this considered
enough for modern x86 ?

It's definitively not enough for Xen (either dom0 or domU), which is
why Xen uses a different vector/spl implementation. As I'm working
on PV drivers for HVM guests it's time to revisit this.
I have two options:
a)  do not touch the x86 native spl implementation, and use a special
    vector for handling Xen events. The event vector will add
    bits to the ci_ipending mask so that it's called again on spllower.
    x86 bare metal is untouched but Xen will be less efficient.

b)  expand ci_ipending to a two-level bitmask, which would give us
    1024 (32*32) interrupt source. This would allow to share
    more code with xen, at the expense of a few more instructions in
    spllower() and in interrupt path on bare metal, and some more
    32bit words in cpu_info.

Any red herring with one or the other solution before I start coding ?

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--