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    SubjectRe: [PATCH RT] ehea: make receive irq handler non-threaded (IRQF_NODELAY)
    On Thu, 20 May 2010, Darren Hart wrote:

    > On 05/20/2010 01:14 AM, Thomas Gleixner wrote:
    > > On Thu, 20 May 2010, Jan-Bernd Themann wrote:
    > > > > > Thought more about that. The case at hand (ehea) is nasty:
    > > > > >
    > > > > > The driver does _NOT_ disable the rx interrupt in the card in the rx
    > > > > > interrupt handler - for whatever reason.
    > > > >
    > > > > Yeah I saw that, but I don't know why it's written that way. Perhaps
    > > > > Jan-Bernd or Doug will chime in and enlighten us? :)
    > > >
    > > > From our perspective there is no need to disable interrupts for the
    > > > RX side as the chip does not fire further interrupts until we tell
    > > > the chip to do so for a particular queue. We have multiple receive
    > >
    > > The traces tell a different story though:
    > >
    > > ehea_recv_irq_handler()
    > > napi_reschedule()
    > > eoi()
    > > ehea_poll()
    > > ...
    > > ehea_recv_irq_handler()<---------------- ???
    > > napi_reschedule()
    > > ...
    > > napi_complete()
    > >
    > > Can't tell whether you can see the same behaviour in mainline, but I
    > > don't see a reason why not.
    >
    > I was going to suggest that because these are threaded handlers, perhaps they
    > are rescheduled on a different CPU and then receive the interrupt for the
    > other CPU/queue that Jan was mentioning.
    >
    > But, the handlers are affined if I remember correctly, and we aren't running
    > with multiple receive queues. So, we're back to the same question, why are we
    > seeing another irq. It comes in before napi_complete() and therefor before the
    > ehea_reset*() block of calls which do the equivalent of re-enabling
    > interrupts.

    Can you slap a few trace points into that driver with a stock mainline
    kernel and verify that ?

    Thanks,

    tglx


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