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linuxreal-timeterminologyxenomai

Real time thread priority in user space

From: http://www.xenomai.org/documentation/xenomai-2.3/pdf/Life-with-Adeos-rev-B.pdf

The above behaviour is to be opposed to what happens with RTAI/LXRT for instance, where threads migrating to the Linux space actually lose their real­- time priority in the same move, by inheriting the lowest priority defined by the RTAI scheduler.

There must be some reason behind this design decision. I wish to understand what kind of advantages can it offer - I mean when the real time thread is shifted to userspace, it gets a low priority (and therefore can be preempted by a high priority real time thread running in kernel space). Are there some assumptions behind this design decision?

Solution

  • Two assumptions:

    1. Threads don't spend much time in kernel space.

    2. Thread in kernel space tend to hold resources that need to be released as quickly as possible.