Hi everyone

I have applied an RT kernel on my raspberry pi. Now I would like to isolate the CODESYS runtime to run on one core. How do I do that? I checked running processes using the htop command and found multiple instances of CODESYS runtime. How do I isolate them all into a single core?

I've been following this guide here but couldn't it working: http://www.comfilewiki.co.kr/en/doku.php?id=comfilepi:improving_real-time_performance:index

I make a little patch to /etc/init.d/codesyscontrol

  ....
    do_status
    if [ $? -eq 0 ]; then
        rm $PIDFILE
        echo "Error: Failed to start codesyscontrol"
        exit 1
    else
        PID=$(cat $PIDFILE)
        taskset -p 1 $PID >>/root/codelog.txt
        renice -n -20 -p $PID >>/root/codelog.txt
        tuna --threads $PID --priority=RR:99
        IRQBALANCE_BANNED_CPUS=3 irqbalance --foreground --oneshot
        echo 0 > /proc/sys/kernel/numa_balancing
        echo never > /sys/kernel/mm/transparent_hugepage/enabled
        echo 0 > /sys/kernel/mm/ksm/run
        echo "codesyscontrol started"
    fi
   ....

I use a RT preempt patched kernel. (Starting from 5.15 no more patch are needed, RT is merged in mainline and you need only configure and rebuild)
- taskset move codesys to core 1 (You can select core for runtime from Task Group in Task configuration, I use 0)
- renice set nice level to maximum (-20)
- tuna set scheduler type RR and priority to 99 (Maximum on realtime kernel)
- IRQBALANCE_BANNED_CPUS=3 irqbalance --foreground --oneshot
turn off interrupts from cores 0 and 1 (mask 0x03)
- the other options may change between various distros, and could improve jitter.

On a rpi4 on native ethernet I reached a jitter < 100us (In last test < 68us in one hour), on a rpi3 is not possible due ethernet via USB.

In kernel command line (/boot/cmdline.txt) I add isolcpus=0,1 to isolate core 0 and 1 from OS management.