[tulip] Problems with IRQs on multiport cards

[Donald Becker]

On Wed, 13 Sep 2000, Jonathan Earle wrote:

> Can the individual ports on a Zynx 4 port card be assigned unique IRQs (even
> via a dirty hack)?

The INT-to-IRQ mapping is unique to the specific motherboard.  Only the
motherboard BIOS can set up the mapping, including configuring the PCI
bridge on the multiport card.

The BIOS may have set up an alternate APIC map, so turning on the APIC code
may result in different IRQ map.

It may also be possible to use an ACPI-language entry point to the BIOS to
change the IRQ mapping, but this is error prone.


>  We're noticing a problem with dropped packets due to,
> what I interpret as being the problem, IRQ conflict/contention.  With higher
> bitrates, I've noticed than not all of the packets which enter the box via
> one port on the Zynx card, leave the box via another port if the two ports
> share the same IRQ.  If lower bitrates are used, the problem appears to
> diminish.  We have up to two of these cards in the same box.
> 
> Kernel version used is 2.4.0-test4.

Verify that the interrupt count is increasing for each port.  It may be that
only eth0 is generating interrupts.

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Beowulf-II Cluster Distribution
Annapolis MD 21403