Re: [RFC] killing the NR_IRQS arrays.

From: Eric W. Biederman
Date: Fri Feb 16 2007 - 14:02:44 EST

Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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...

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