MetaIRQs are described in docs and exercised in tests, but there's no
sample explaining how they are intended to be used to perform
interrupt bottom half processing.
This simple tool spawns a set of worker threads at different
priorities (some cooperative) which process "messages" (which require
CPU time to handle) received from a fake "device" implemented with
timer interrupts. The device hands off the events directly to a
MetaIRQ thread which is expected to parse and dispatch them to the
worker threads.
The test demonstrates that no matter the state of the system, the
MetaIRQ thread always runs synchronously when woken by the ISR and is
able to preempt all worker threads to do its job.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
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