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    SubjectRe: [RFC] killing the NR_IRQS arrays.
    Date
    Jeremy Fitzhardinge <jeremy@goop.org> writes:

    > Eric W. Biederman wrote:
    >> So I propose we remove all assumptions from the code that we actually
    >> have an array of irqs. That will allow for irq_desc to be dynamically
    >> allocated instead of statically allocated saving memory and reducing
    >> kernel complexity.
    >>
    >
    > Sounds good to me. In Xen we have 1024 event channels which we need to
    > map down into a smaller irq. Aside from the complexity of maintaining a
    > mapping table, that's not a huge issue for now, but when we start
    > exposing pci devices to guests it all becomes more complex. The ideal
    > for us is to simply use event channel == irq, which this would allow.

    Well you shouldn't need to wait just run with a kernel with NR_IRQS >= 1024.
    1024 is stretch but it isn't to bad. There are already x86 boxes that have
    more pins on their ioapics then that. So x86_64 and with this latest
    round of patches from Len Brown and I i386 should be able to support that.

    On the other side 1024 looks extremely limiting for exposing pci devices.
    If someone gets serious about pushing what is legal with MSI-X you may be
    in trouble. As a single device is allowed to have 4096 interrupts. Not
    that I can think of a user for so many but...

    Eric
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