Re: what is IRQ sharing?
- From: Dances With Crows <danSPANceswitTRAPhcrows@xxxxxxxxx>
- Date: Thu, 22 Feb 2007 13:44:38 -0600
On Fri, 23 Feb 2007 03:56:27 +0900, kerneloops staggered into the Black
Sun and said:
what is IRQ sharing?
clairissa:~$ grep 11 /proc/interrupts
11: 13516564 XT-PIC ehci_hcd:usb1, uhci_hcd:usb2,
uhci_hcd:usb3, uhci_hcd:usb4, yenta, ipw2200, fglrx
As you can see, ehci_hcd (USB2 chip), uhci_hcd (USB1 chip), yenta
(PCMCIA controller), ipw2200 (802.11bg card), and fglrx (evil
binary-only module for ATI Radeon) are all *sharing* ISA IRQ 11. When
IRQ 11 fires, the kernel must figure out which module handles the event
that happened, and pass the event to that module. PCI devices do this
fairly well in most cases, so long as you don't have many high-traffic
devices on the same IRQ. ISA devices had real problems sharing IRQs.
This is important because the traditional x86 arch only had a few
available IRQs. 5, 10, and 11 were the only ones that were guaranteed
to be free. (7 if you disabled your parport, 3 and 4 if you disabled
your 9-pin serial ports.) IO-APIC made it possible to use IRQs 16..31,
though, and on the x86_64, you can use IRQs 16..254. So it's not quite
as important as it used to be. HTH,
--
Q: How many surrealists does it take to change a light bulb?
A: Two. One to hold the giraffe and the other to fill the bathtub
with brightly colored machine tools.
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see
.
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