Re: Channel Access performance with RTEMS on MVME5500

[Heinz Junkes via Tech-talk <tech-talk at aps.anl.gov>]

Hello Alex,
the ‘USE_POSIX_THREAD_PRIORITY_SCHEDULING = NO’' is an EPICS thing.
I don't know exactly what this does as I have never used it with RTEMS.
I think that cancels out the whole point of a priority-based system ;-)

All your jobs have a very low priority 253 (in RTEMS) and priority 2 in Posix.

Based on my gut feeling, I would recommend setting back to USE_POSIX_THREAD_PRIORITY_SCHEDULING=YES and then
in rtems_init for POSIX_Init() to set the priority high. You can use the code element I sent to you in the last tech-talk-reply.
Then all the interrupt handlers will also get a high priority and I assume that the crashes will also go away.

Would you like to try that?

Good luck,
Heinz



> On 20. Mar 2025, at 12:50, Wells, Alex (DLSLtd,RAL,LSCI) <alex.wells at diamond.ac.uk> wrote:
>
> Hi Heinz,
>
> Thank you for the information. There's definitely something fishy going on with the thread priorities somewhere; it seems that everything is being started with the same priority.
>
> I will also note that we are building RTEMS with "USE_POSIX_THREAD_PRIORITY_SCHEDULING = NO". This appears to be required, as we use EPICS Mutexes in an interrupt context, and if we leave this set to "YES" we see a crashes. Could this be related to the oddities below?

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