On Wed, 1 Sep 1999, Michael J. Rensing wrote:
> Does anyone know if it is possible to re-assign the interrupts for a
> Symbios SYM22910 host adapter? It's using the SYM53C8xx drivers.
>
> I've got a Beowulf console node with two dual port host adapters, a
> Mylex host adapter, and a four port NIC. Four IRQ's are being used at
A single PCI BUS has 4 interrupt lines INTA#, INTB#, INTC#, INTD# and
no more. On common PCI BUSes, these lines are shared by PCI devices and
are routed to the interrupt controller as 4 IRQ vectors.
> least twice, and several aren't being used at all. For optimum
> performance, I'd like to re-assign the most heavily used interrupts.
Some motherboard setup softwares allow some configuration of INT lines
routing, but if you are using more than 4 PCI devices or multi-function
devices, not all combinations will be possible. If your MB does not
support such an INT/IRQ setup facility, you can try to move PCI boards
between PCI connectors and see what happens to INT#->IRQ routing.
A PCI device driver must be aware of the INT line being shareable and so,
it must check if it has work to do from its interrupt routine and just
return if nothing is to be done. This is generally performed by reading
some device IO register and testing some flag(s) and is kind of negligible
load.
What you may want to do may be to let the most heavily used PCI devices
not share their IRQ, but given the number of PCI device/functions of your
system, other IRQs will be more heavily shared, and this may have adverse
effects.
Could it be possible that the INTx#->IRQy routing of your system be just
fine ? ;-)
G�rard.
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