RT process priority > Interrupts ?

[Valdis.Kletnieks at vt.edu]

On Thu, 09 Apr 2015 15:30:42 +0900, manty kuma said:
> A missed IRQ is not considered fatal but where as missing the upper time

Are you *sure* that ignoring an IRQ for an arbitrarily long time is non-fatal?

(Hint - it may not be fatal to the *kernel*. Think bigger....)

> limit for an RT process will be considered fatal. Hence I think, as a
> simple solution, the process should not be preempted.

What does missing an IRQ mean for the following:

1) Hardware that's spewing IRQs on a constant basis (think "data acquisition"
where you have a A/D converter handing you 4K of data every millisecond, whether
you're ready or not). If userspace decides to go compute-bound for 2ms in
an RT thread (bad idea but sometimes it happens), how many blocks of data
do you lose?

2) What does missing an IRQ do to the latency of a *different* RT thread
that's waiting for I/O completion?

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