29/10/15 21:45, Carsten Emde:
Is the codesyscontrol system running at priority above 80 or below? If
above, then at least the second result makes sense, since on a
single-core system only the one task that runs at highest priority is
the real-time task that enjoys the worst-case latency of the system. All
other tasks do not. If, however, priority 80 of the cyclictest task is
the highest priority of all tasks, then you may have detected a problem
that needs to be fixed.
I executed codesyscontrol without setting any priority and scheduling
policy. When i execute chrt -p <pid_of_codesyscontrol>, it shows:
pid 1532's current scheduling policy: SCHED_OTHER
pid 1532's current scheduling priority: 0
But now i think it wasn't true. After your advice i execute cyclitest
with maximum priority(99), and results became deterministic.
./cyclictest -t1 -p 99 -n -i 10000 -l 10000
# /dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 4.95 4.39 2.80 2/77 1533
T: 0 ( 1533) P:99 I:10000 C: 10000 Min: 13 Act: 20 Avg: 20 Max:
62
Note that cyclictest is intended as a placeholder of a real-time task
for people who do not have their own user-space real-time project, for
example kernel developers and board manufacturers. Once you have your
own real-time application, you better equip it with internal real-time
checks in a similar way as cyclictest does it, but you should not run
cyclictest in parallel.
Thanks,
-Carsten.
The real goal for me, indeed, is running codesyscontrol, which is runs
IEC 61131-3 industrial programs.
First i tried codesyscontrol run on Linux without RT-patch. It was
sporadic multiplying of cycle time of IEC 61131-3-program. And then i
decide to try RT-patch. But multiplying of cycle time in CodeSys is
still appears, even when it runs with 99 priority. So now i think it's a
problem in CodeSys runtime system(as i convinced with your advice, that
RT-patch works well), i wrote this issue to their support(because we are
buying binary package of CodeSys, i can't do with this any programming
hacks, but only administrative).
Thank You very much for help!
--
Best regards, Sergey.
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