[Xenomai-help] Propagating interrupts

[Xenomai-help] Propagating interrupts

[Jeff Webb]

I have read that propagating interrupts to Linux is a bad idea for RT applications.  I am trying to understand what happens when I install an interrupt handler via the userspace POSIX skin like this:

  pthread_intr_attach_np (&ctr_intr, irq_number, PTHREAD_IPROPAGATE);

My RT thread waits on this interrupt using:

  pthread_intr_wait_np(ctr_intr, NULL);

Here is my understanding of what happens when I get an interrupt on this IRQ.  The Xenomai interrupt handler is executed, which wakes up my RT thread.  The interrupt remains masked until the Linux interrupt handler is executed.  The linux interrupt handler processes the interrupt, and then re-enables the IRQ.  Now the RT thread can receive more interrupts.

Is this basically correct?

-Jeff

Re: [Xenomai-help] Propagating interrupts

[Jan Kiszka]

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Jeff Webb wrote:
> 
> I have read that propagating interrupts to Linux is a bad idea for RT
> applications.  I am trying to understand what happens when I install an
> interrupt handler via the userspace POSIX skin like this:
> 
>  pthread_intr_attach_np (&ctr_intr, irq_number, PTHREAD_IPROPAGATE);
> 
> My RT thread waits on this interrupt using:
> 
>  pthread_intr_wait_np(ctr_intr, NULL);
> 
> Here is my understanding of what happens when I get an interrupt on this
> IRQ.  The Xenomai interrupt handler is executed, which wakes up my RT
> thread.  The interrupt remains masked until the Linux interrupt handler
> is executed.  The linux interrupt handler processes the interrupt, and
> then re-enables the IRQ.  Now the RT thread can receive more interrupts.
> 
> Is this basically correct?

Yes, the Linux domain can cause priority inversion /wrt the real-time
domain trying to handle the same IRQ line. That's true for any
deterministic/indeterministic IRQ handler combination, not only under
Xenomai.

Jan


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