Re: balance interrupts

[Julien Oster <lkml-2315@mc.frodoid.org>]

Len Brown <len.brown@intel.com> writes:

Hello Len,

> Most IO-APIC systems have PCI interrupt lines hard-wired directly to
> IO-APIC interrupt pins.  If an interrupt isn't where you want it to be,
> you need to physically move a card to another slot so that it gets a
> different wire.  A board with decent documentation will tell you what
> slots get which interrupt wires.

Ah, my board has that kind of documentation. Well, then I might do
just this - or see if my board can do that for me. Also, I'd really
want to know if maybe I can split apart the two SATA channels.

> Today basically all boards have also a PIRQ router that is used to map
> these PCI interrupt wires down into PIC interrupt inputs for when the
> system is in PIC compatibility mode (eg. when running the booter). 
> Sometimes they can also re-map interrupt lines in IO-APIC mode.

Ah, that sounds interesting.

> Since your system is running in ACPI mode, the output of acpidmp is
> needed to figure out exactly that the BIOS is saying the board can do.
> The output of lspci -l with this will tell us if we can split apart the
> SATA interrupts, or if they're wired together.

Hmm. I got pciutils 2.1.11 (those claim to be the latest), but my
lspci doesn't know "-l". I attached the output of lspci -vvv to this
mail, however. Maybe it's of any use.

I attached the output of acpidmp to this mail as well. It's a
collection of hexdumps. Since I have no internal knowledge about ACPI
or IO-APICs, I can't do anything with it...

> Another twist is that sometimes enabling/disabling devices in the BIOS
> SETUP will change how the BIOS configures the hardware and make more
> interrupts available.  Here, for example, USB seems to be low hanging
> fruit on a high-rent >= 16 IRQ.

Sorry, I didn't quite understand your last sentence with the fruits
and the rent. I suppose it's some expression, but I'm not a native
english speaker.

But I already disabled everything I don't need in the BIOS (I need
USB, however) and the situation didn't improve very dramatically. At
least I can't see of any devices having changed place in the IRQ list,
only that the devices I deactivated have gone. I also enable "Reset
ESCD data" in the BIOS to encourage things getting rearranged.

> If you're not using ACPI features, you might also try booting with
> "acpi=off" and see if the chip-set PIRQ router does a better job for
> you.

Hmm. If I remember correctly the IRQs stay XT-PIC if I don't enable
ACPI, regardless wether IO-APIC is enabled or not. And the old style
PIC of course leads to the result of my interrupts being very
crowded...

Thanks for your help!
Julien