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SubjectRe: [PATCH RT] ehea: make receive irq handler non-threaded (IRQF_NODELAY)
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.


>> queues with an own interrupt each so that the interrupts can arrive
>> on multiple CPUs in parallel. Interrupts are enabled again when we
>> leave the NAPI Poll function for the corresponding receive queue.
> I can't see a piece of code which does that, but that's probably just
> lack of detailed hardware knowledge on my side.
> Thanks,
> tglx

Darren Hart
IBM Linux Technology Center
Real-Time Linux Team

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