[Xenomai] ipipe + PREEMPT_RT

Jan Kiszka jan.kiszka at web.de
Sat Mar 18 09:45:25 CET 2017

On 2017-03-18 07:09, Mike Galbraith wrote:
> (oops, sent before subscription confirmation.. wash/rinse/repeat)
> Greetings,
> Seeing PREEMPT_RT in ipipe source, I got curious, extracted 4.4.43, and
> wedged it into 4.4.54-rt, but there are a couple places that replace a
>  spinlock_t (not raw) with an ipipe_spinlock_t, which cause build woes
> for PREEMPT_RT.  I ifdefed those problematic spots back to spinlock_t
> for grins, and surprisingly, my x64_64 desktop box booted, and does a
> decent impersonation of a functional box.. which left me wondering
> whether there's a preparatory patch for PREEMPT_RT somewhere, or
> whether the PREEMPT_RT bits are WIP (or leftovers).

A couple of times, I-pipe with Xenomai has been used in combination with
PREEMPT-RT. That basically created 3 prio groups: regular Linux tasks,
real-time Linux tasks hardened by PREEMPT-RT and above that
I-pipe/Xenomai. However, the integration of both patches was never
really fun.

Some fragments of those efforts you still find in the code, but I think
they haven't been stressed for a while. And, as you noticed, they do not
work as-is. I wouldn't be surprised if your ad-hoc fix does not yet
solve the issue, and a Xenomai use case would break. The semantics of
each real-time patch set is already tricky on its own...

That said, I suppose such integration will return automatically once
PREEMPT-RT makes it upstream.

Was your question just out or curiosity, or is there a potential use case?


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