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SubjectSanity checks and interrupts
I'm sure there's a FAQ about this somewhere, although I have done some 
googling and not found much helpful info.

Anyhow, I wish I could give you more information on my computer, but I'm
at work, and the computer is at home. In short, it's running RH9 with
the latest up2date kernel (2.4.20-??). The motherboard is an Abit KD7
which is a KT400 MB.

How, everthing seems to work fine, but in my (very slow) research for
system sanity checking, I've noticed people talking about interrupts.
Well, so I dumped /proc/interrupts and looked at it.

To begin with, I notice that there are only "XT-PIC" interrupts. Why is
that? From what I've read, others have "AT-PIC" and "APIC" interrupts
as well. Being a modern MB, I would expect to see something else. Does
that mean there's a problem?

Secondly, I noticed that both the network card (well, I have two, one
built in, the other PCI, and I don't remember which) and my 3ware RAID
controller (7000-2 or something) are sharing the same interrupt (11, I
think), and in fact, there are two or three other devices on that same
interrupt, which seems unbalanced to me. Is THAT a problem? It is,
after all, only a single processor box, but could there be any kind of
performance issue because of this? How about stability?

I'm typing this email on a RH7.2 box running 2.4.18-27.7.x, and I
checked /proc/interrupts here as well. This is what I get:

CPU0
0: 663851803 XT-PIC timer
1: 208891 XT-PIC keyboard
2: 0 XT-PIC cascade
8: 1 XT-PIC rtc
9: 0 XT-PIC usb-uhci
10: 0 XT-PIC Intel ICH2
11: 103158523 XT-PIC usb-uhci, eth0, nvidia
12: 4313520 XT-PIC PS/2 Mouse
14: 1245414 XT-PIC ide0
15: 8417399 XT-PIC ide1
NMI: 0
ERR: 0


What decides that three devices should be on 11 but only one on 10 or
12? Why not two on each? Why isn't one on 13? I know that not all
devices can have dynamically assigned interrupts.

And why is nothing hooked up to interrupts 3 thru 7? I'm sure there's
some legacy issue to do with this, although if they refer to things
which have been deprecated, I'm surprised modern MB's don't reassign them.


And another thing... wrt PCI devices, I know that each slot is assigned
one of four interrupt lines in rotation. My MB has 6 slots, although
one of them is the "you can't use this" slot for AGP. (BTW, more than 4
slots per bus is a PCI spec violation.) If my NIC is in the last slot
and the 3ware is in the first, maybe they share interrupt signal lines.
Perhaps moving one of them would change things. But would that make
one iota of difference?


Thanks!

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