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Reducing Jitter

arj3090
2019-07-09
2019-07-26
  • arj3090 - 2019-07-09

    I have been experimenting with reducing jitter on a Raspberry Pi with the Preempt RT patch. The one thing I found that seemed to help was to set the CodeSys process to a nice level of -20. My test is not very scientific, but enough to see results. I have a program with 5 tasks and they are all set to free floating processor core use. My before and after jitter results:

    Before -> After
    129 -> 95
    157 -> 117
    154 -> 66
    102 -> 62
    521 -> 147

    So my question is whether changing the nice value could have other side effects?

    This is the method I used to change the CodeSys nice value:

    Connect using SSH
    cd /etc/init.d
    sudo nano codesyscontrol

    insert the "--nicelevel -20" into the following line :

    start-stop-daemon --start --background --make-pidfile --pidfile $PIDFILE --nicelevel -20 --chd$

    reboot

     
  • eschwellinger

    eschwellinger - 2019-07-12

    Hi,
    which jitter do you see , before you start changing anything?

    BR
    Edwin

     
  • arj3090 - 2019-07-26

    Edwin Schwellinger hat geschrieben:
    Hi,
    which jitter do you see , before you start changing anything?

    These are the values before and after changes:
    Before -> After
    129 -> 95
    157 -> 117
    154 -> 66
    102 -> 62
    521 -> 147

    This was only a short term test over a few hours so it may not be very accurate.

     

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