Until today, I haven't found the need to concern myself with IRQ settings in almost a decade, but I have a 3ware 9650SE RAID controller and Intel 915 video sharing the same IRQ, and I'm experiencing both very slow disk access and Xorg freezing. This is on a new installation of Ubuntu Lucid (10.4). I didn't have this problem with the same hardware running Hardy or Intrepid.
I've looked at all my motherboard (ECS 945GCT-S 1.0) BIOS settings, and the only ones that seem relevant are 1) allocate IRQ to PCI VGA (assign IRQ to PCI VGA card if it requests one, or do not assign even if it requests one) and 2) APIC mode (include ACPI APIC table pointer to RSDT pointer list). Changing #1 doesn't affect the IRQ assignments, and changing #2 results in RAID and video sharing a different IRQ. I've disabled the motherboard ATA, SATA, USB, serial, and NIC. i915 and 3w-xxx still share an IRQ. I've moved the RAID card from one PCI Express slot to the other PCI Express slot. Still sharing. I skimmed the PCI Plug-and-Play HOWTO, but didn't find anything helpful. Can I cause the OS to affect IRQ assignment? If so, how? I'd appreciate any other suggestions. -- Phil Mocek
