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    SubjectRe: NIU driver: Sun x8 Express Quad Gigabit Ethernet Adapter (perf + regression IRQs)
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    From: Jesper Dangaard Brouer <hawk@diku.dk>
    Date: Wed, 19 Nov 2008 23:58:12 +0100 (CET)

    > Well that was not the real cause of the performance loss. Because
    > on kernel 2.6.27 I get really good performance (900-1200kpps)
    > compared to 2.6.28 (git net-2.6).
    >
    > The cause of this problem (tracked down together with Robert Olsson)
    > is that on 2.6.28 I have a lot less IRQs available. It seems max 34
    > IRQs.
    >
    > Due the reduced number of IRQs the NIU driver cannot get enough IRQs
    > to the interfaces, and starts to use "IO-APIC" based IRQs.

    This is almost certainly related to the driver unload bug.

    I know you ran into unbuildable/unbootable kernels during a bisect,
    but you really need to track down this regression.

    There were a lot of IRQ changes, especially on x86. The sequence is
    something like:

    1) dyn irqs
    2) APIC/IO_APIC handling integration
    3) by-hand REVERT of dyn irqs, it was done by hand in order to not
    lose the #2 changes
    4) interrupt remapping support



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