MrsP Semaphore and EDF-RMM

Sebastian Huber sebastian.huber at
Wed Aug 1 05:26:25 UTC 2018


On 31/07/18 15:47, Rúben Gonçalves (1150785) wrote:
> When making some experiments to the behaviour of RTEMS in SMP 
> configured with EDF and Rate Monotonic Manager we also noticed that 
> when a *periodic task* tries to obtain a semaphore created with the 
> Multiprocessor Resource Sharing Protocol (MrsP) the application 
> returns the status code "RTEMS_INVALID_PRIORITY".
> We presume this is due to the fact that MrsP semaphore obtain function 
> tries to raise the priority of the task to the previously defined 
> priority ceiling and since the current priority is given by EDF (in a 
> way don't understand) (using the rate monotonic) the function is not 
> implemented to deal with that.
> Does it make sense? Is it any accurate?

the EDF scheduler uses the deadline of a task to determine its priority. 
The earlier the deadline the higher the priority (lower priority value). 
The priorities associated with a deadline are higher than the priorities 
which can be specified by the normal API.

> If not, how can MrsP be correctly used with these configurations?

This is currently an unsupported use case. You can use the OMIP mutexes 
together with the EDF scheduler. Are there schedulability analysis 
results for MrsP + EDF?

Maybe the MrsP implementation can be changed to use the highest priority 
of the executing thread and the mutex object.

Sebastian Huber, embedded brains GmbH

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