Re: [Xenomai-help] Propagating interrupts

[Jan Kiszka <jan.kiszka@domain.hid>]

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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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