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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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