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    SubjectRe: [RFC][PATCH -rt] irqd starvation on SMP by a single process?


    On Fri, 12 May 2006, Ingo Molnar wrote:

    > ah. This actually uncovered a real bug. We were calling __do_softirq()
    > with interrupts enabled (and being preemptible) - which is certainly
    > bad.

    Hmm, I wonder if this is also affecting Mark's problem.

    But since I showed that if hardirqs_disabled and running PREEMPT not
    PREEMPT_RT, disable_irq can call schedule. This is done in
    drivers/net/3c59x.c. It has a watchdog timeout calling disable_irq, which
    calls synchronize_irq which might schedule:

    void synchronize_irq(unsigned int irq)
    {
    struct irq_desc *desc = irq_desc + irq;

    if (irq >= NR_IRQS)
    return;

    if (hardirq_preemption && !(desc->status & IRQ_NODELAY))
    wait_event(desc->wait_for_handler,
    !(desc->status & IRQ_INPROGRESS));
    else
    while (desc->status & IRQ_INPROGRESS)
    cpu_relax();
    }

    -- Steve

    >
    > this was hidden before because the smp_processor_id() debugging code
    > handles tasks bound to a single CPU as per-cpu-safe.
    >
    > could you check the (totally untested) patch below and see if that fixes
    > things for you? I've also added your affinity change.
    >
    -
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