[openib-general] IRQ sharing on PCIe bus

[Roland Dreier]

    yipee> Hi, My setup is a 3GHz Xeon (x86_64) with a 2.6.13.2
    yipee> kernel. A Mellanox memfree PCIe ddr HCA is connected.  Why
    yipee> do I see IRQ sharing although I'm using msi_x and PCIe? 
    yipee> Doesn't IRQ sharing only happen on older non PCIe busses?

I think the messages you see are coming from the ACPI interrupt
routing that is done when the driver calls pci_enable_device().
However, if you use MSI-X then that interrupt won't actually be used.
If you check /proc/interrupts you should see ib_mthca using 3
non-shared interrupts.

BTW, for "INTx emulation" on PCI Express, there are no physical
interrupt lines -- interrupts are asserted and deasserted with
messages.  So PCI Express interrupts are unshared.  However, the PCI
Express host bridge turns those interrupts into real interrupts to the
system's interrupt controller, and for that part of the story, it's
entirely possible for two different PCI Express devices to end up
sharing the same interrupt line.

 - R.