Robert Jonsson wrote: >Thursday 09 October 2003 12.26 skrev wes schreiner: > > >>jordan muscott wrote: >> >> >>>Ok to be honest I'm not gonna switch distros...... but are you saying >>>that Redhat offers you extra software that allows you to change the >>>IRQs that your pci cards are on? >>> >>> >>There is no such software on any distro. Your motherboard's BIOS decides >>which PCI slots get which IRQs. In a few motherboards the BIOS lets one >>select which IRQs get assigned to certain slots, but most don't. So with >>most motherboards all one can do is move cards around to different slots >>and then see what IRQ gets assigned. If your sound card and your >>ethernet card are sharing an IRQ, that's because those PCI slots used >>both have the same IRQ assignment. If you swap just those two cards >>slot-for-slot they will end up with the same IRQ again. Try moving just >>one of the cards to another slot. If all of your slots are full then >>move multiple cards. >> >>On some motherboards with some processors you can turn on Local APIC >>support in your kernel config and get more IRQs to work with. Dual >>processor motherboards, even if they have only one CPU installed, can do >>this to get more IRQs. If you have dual CPUs you should already be >>running a SMP kernel and you probably don't have IRQ assignment >>problems. If you do, it's back to juggling cards. >> >>wes >> >> > >Hi, > >I'm pretty sure I've read that APIC is a no no and should be avoided. > > I'd like to see what you read. In my experience it either works or it doesn't. One can't avoid using APIC interrupts in a dual-processor system. >Here's a link to some interesting info about "normal" IRQs in a PC. There is >more to it than just having an "OWN" IRQ, they have different priorities. > >http://myweb.cableone.net/eviltwin69/Arcana.html#IRQs > >See also (the source) >http://www.djcj.org/LAU/guide/Low_latency-Mini-HOWTO.php3 > > >/Robert > > > Yes, that HOWTO has good info, as far as it goes. One thing I would add though, is that when using non-APIC interrupts the interrupt priority is not fixed in stone (or silicon, as it were). Using the program "irqtune" one can change interrupt priorities (see http://www.best.com/~cae/irqtune ). I havn't used irqtune in a while, not since kernel 2.2 days, so I'm not altogether sure that it works correctly with 2.4.x kernels. On Debian it is in the "hwtools" package. Hmm, I just tried it on a box with a 2.4.21+lowlatency kernel and it seems that it worked, though it gave some warnings. I can't really test if the IRQ priorities have changed though. YMMV. wes
