[openib-general] ip over ib throughtput

[Roland Dreier]

    Roland> Based on all the trouble I've seen with interrupt routing
    Roland> on various systems, I'm thinking it's worth adding a test
    Roland> to the driver to make sure that it can receive
    Roland> interrupts...

    Grant> Hrm...only if the test completes quickly on success.

Yes, all we have to do is try a NOP FW command and see if it generates
an interrupt on completion.  This will succeed within a millisecond in
the extremely worst case if interrupts are working, so even the
failure case will be quick.

    Grant> TBH, I would expect IRQ lines to work on *ALL* platforms.
    Grant> Basic part of PCI compliance dictates this.

You would expect this but the supply of BIOS and kernel ACPI bugs
seems inexhaustible...

    Grant> It's clear not all platforms support MSI and the failure
    Grant> mode may vary. So a test for MSI or MSI_X would be good.
    Grant> And then the code can warn "MSI[-X] Failed - falling back
    Grant> to IRQ Line".

That's a good idea but it may take me a little while to get to it
because it's a little bit of a pain to unwind our MSI configuration
after we get to the point where we can see if it worked or not.  For
now we'll have to be satisfied with a diagnostic telling you to try
again without MSI...

 - R.