Re: [PATCH] 2.6.1-mm2: Get irq_vector size right for generic subarchUP installer kernels

[Zwane Mwaikambo]

On Thu, 15 Jan 2004, James Cleverdon wrote:

> > In my opinion we should be breaking after we've exceeded the maximum
> > external vectors we can install. This will of course mean less than
> > the number of RTEs. James have you actually managed to use the devices
> > connected to the high (over ~224) RTEs?
>
> No, I haven't exceeded the available vectors, but wli has on a large NUMA-Q
> box.

Yes i believe the 8 node NUMA-Qs do this easily.

> The x440 and x445's problems are pre-reserving lots of bus numbers in the
> BIOS, more than one per PCI slot.  They must be anticipating PCI cards with
> bridge chips on them.

For some odd reason i thought we had dynamic allocated MP busses.

> I believe that the reason for irq_vector being so large is to allow IRQ (and
> eventually vector) sharing.  The array is to map from RTE to vector.

What i'm trying to say is that the current code will behave badly when you
actually do encounter a system with that many RTEs, the actual array
being that large isn't a problem, the problem is what's going on in
assign_irq_vector() and later on with set_intr_gate(). By that i mean;

- The interrupt[] stub in entry.S is written with 256 irqs in mind so it
wouldn't be able to pass higher irq numbers to do_IRQ in it's current
state.

- "Wrapping" in assign_irq_vector means that you overrite previously
assigned vector entries in the IDT with whatever interrupt[irq] you happen
to be installing at the time. To avoid this you should not be allowing
more than ~224 vectors to be handed out by assign_irq_vector(), with the
patch and the current code, this is possible.

Lastly i think we should avoid sharing vectors, going the IA64 route and
setting up irq handling domains of sorts would allow for easier scaling
both up and down.

Thanks,
	Zwane
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/