Priority inheritance?

[Stanislav Meduna <stano@meduna.org>]

Hi,

strictly speaking not a linux-rt specific questions but I think
that the folks here have the needed experience and knowledge:
what is the relation of
  pthread_mutexattr_setprotocol(&attr, PTHREAD_PRIO_INHERIT);
and scheduler class used for a particular thread? Does the priority
inheritance work across all threads in the system or is it limited
to one scheduling class?

Specifically: my application has some SCHED_RR threads with fixed
priorities and realtime needs and a few that are quite low-prio,
actually have the SCHED_OTHER semantics and I don't want them
to count against the time spent in RT (keyword: throttler).

I need to occasionally queue data from from the RT-ones to
the low-prio ones, so for short periods of time I need to lock
a mutex. With it comes the question of priority inversion.

Can I leave the low-prio threads at SCHED_OTHER and rely on
the PTHREAD_PRIO_INHERIT to boost their priority in case they
were preempted with the lock held and the RT-thread needs
to lock it too, or do they have to be SCHED_RR too?

Thanks
-- 
                                    Stano