POSIX vs RTEMS Classic Scheduling Priorities

rtwas rtwas at comcast.net
Sat Feb 13 06:54:56 UTC 2010


I'm developing an app that uses both Rtems-Classic Tasks and Posix Threads.
The priority systems are somewhat different. Rtems has a priority numbering
system running from 0-255 with the smaller number being higher in priority.
Posix on the other hand uses larger numbers to represent higher priorities.
The exact span of of Posix appears to be implementation specific (linux 
being 1-99).

To properly schedule my threads I'll need to adjust the priorities of
Rtems (networking etc) tasks and my main pthread such that the main 
pthread has
the higher priority.  To do that I'll need to know how to relate the two 
priority numbering
schemes (so I can pick the right priority numbers for each priority 
scheme). My
assumption is that they can both be viewed as number-lines and that with 
the proper
scaling and offsets the two priority number-lines can be correlated. 
Reading through
the docs I have been unable to locate any information that would pin 
down how to
relate the two priority systems.

Help appreciated.

Robert W.

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