[Asterisk-Users] Re: PCI front mount chassis?

[James H. Cloos Jr.]

>>>>> "Steven" == Steven Critchfield <critch at basesys.com> writes:

Steven> As I understand the PCI spec, there are 4 interrupt lines
Steven> called A,B,C, and D. In slot 1, They appear in that order. In
Steven> slot 2 they shift, in slot 3 they shift and again in slot 4.

That is correct, except that all top-shelf systems use multiple pci
busses to spread both the interrupt and the bandwidth load.  This
is especially true of systems with the pci-x slots.

Pci-express I believe takes that one further and uses a switch and
serial links, doing for the expansion cards what 10-baseT did for
ethernet.

At that point -- especially on the opteron and the 64bit xeons -- the
pics *should* be wired so there is no sharing.

Whether even such a box as that can deal well with, say, seven cards
generating 1 kHz of ints, plus the timer doing so (2.6 kernels use
HZ=1000 internally on x86 & x86-64, even though it looks like 100
from userspace to maintain compatability with older utils) and 
however many ints the network and disk interfaces generate is a
question left to answer.

(Why seven?  7 x 4(DS1) == DS3.)

At some point, of course, it will be necessary to do what routers
do:  switch from interrupts to polling when the load is high enough.

-JimC