On Thu, 09 Oct 2003 07:49:02 -0500 "wes schreiner" <wes@xxxxxxxxxxxx> wrote: >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 http://www.ibiblio.org/mdw/HOWTO/Serial-HOWTO-8.html#ss8.1 >>>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 > > >
