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Old July 17th, 2019, 07:08 PM   #1
aufisherman
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ControlLogix CPU Usage Varying

Hello,

I am trying to perform the new Rockwell PlantPAx Verification checklist thing.

If execution time is not varying on my tasks, but the CPU usage is varying greatly (20% to 70%) what could be the culprit?

I see that there is an issue, but I cannot find any information on specifically what to look for inside my routines to identify the source of this varying cpu usage.

Any thoughts?


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Old July 17th, 2019, 09:28 PM   #2
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Are you using a lot of timed tasks? CPU usage could be low when not doing an active task, but high when doing so? Not sure how long of a time that "usage" is averaged over.
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Old July 18th, 2019, 06:08 AM   #3
Ken Moore
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Is this batch operation? The number of active event driven tasks would vary the cpu task.
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Old July 18th, 2019, 11:27 AM   #4
aufisherman
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This is not batch. It is a continuous process and we are using periodic tasks. My 1000ms task that has all of IO and regulatory control FBDs is the one that is varying from 50-95% cpu usage while scan time varys between 170,000-220,000 microseconds.
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Old July 18th, 2019, 11:30 AM   #5
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They are periodic tasks. The culprit is a 1000ms periodic task that has all the IO and regulatory control FBDs. The scan time will hover between 170,000-220,000 microseconds. Sometimes the scan time will stay the same while the CPU usage just climbs from 50% to 99%
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Old July 19th, 2019, 07:02 AM   #6
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So 170 to 220 milliseconds for a routine?
I haven't seen scan times like that since... well, uhhh...
I can't remember when.
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Old July 19th, 2019, 10:58 AM   #7
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Haha. This is one of the only "full DCS" implementations of ControlLogix that I have really worked on. The controllers are being used for process control.

The process library objects that are used for a PlantPAx implementation are very heavy on useless stuff you never need so a lot of overhead.
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Old July 19th, 2019, 07:00 PM   #8
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That's a brutal scan time, but makes sense with a big PAx program. Just curious, what processor are you running and about how much I/O?
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