I don't know how useful this will be. My MB, an A-bit AC7 (10 years old?),
has the option to turn off IRQs for USB and/or video. My first thought was
that would not be useful, but it turns out what it does is turn of the
bios IRQ selection. This means the Linux kernel has to do this... and the
Linux kernel does a better job of allocating IRQs than the bios does. The
ehci IRQ is now on it's own (USB 2.0) where it used to be lumped on 16
with 4 other things. eth0 has it's own irq too, as do both my audio cards.
I was still able to boot from a USB 2 device as well.
So in the case of finding PCI slots that give solo IRQs, it is worth
playing with the bios settings, even things that do not make sense.
Linux-audio-user mailing list