Jan Kiszka wrote:

this is an experimental hack to open the non-rt priority levels of Linux
to Xenomai shadow threads, i.e. allow shadows to be scheduled under
SCHED_NORMAL when in secondary mode. The scenario are typical borderline
threads between RT and non-RT: they share a critical code path with RT
threads, maybe mutex protected, but they are mostly time-sharing threads
which do not need SCHED_FIFO for this.

The patch (be careful, quick-hack!) addresses the prio level 0 in the
ipipe patch, the nucleus/shadow subsystem, and the native skin. A quick
test with the attached demo showed the expected behaviour so far: no
lock-up during busy-waiting in secondary mode, prio-boost when holding
the lock (visible via /proc/xenomai/sched), no obvious side effects.

Any comments? Does this break other things in a subtle way?

An initial comment on the general usage of this extension: since the threads running in SCHED_OTHER/SCHED_NORMAL mode are expected to run non-RT workloads while still being able to use the RT infrastructure for communicating with the rest of the RT system, I think that the best places for creating such hybrids are in the rt_task_shadow (native skin) and pthread_setschedparam (POSIX skin) calls, which would make it clear that a regular Linux thread is involved [and as such needs to be created by a normal call to pthread_create()], which also happens to benefit from the RT infrastructure mainly for communication/sychronization purpose.



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