Control Logix CPU Utilisation

I have a L61 Control Logix processor. It was installed with firmware version 16 and the cpu utilisation was about 50% and the ethernet CPu was about 45%. This controls 16 Powerflex 700VC drives and some PID loops.
I recently flashed the firmware to version 17 and added some basic motor control functionality (on/off/fail) using a add-on insruction which is called 23 times. I noticed that the online browsing is slow so I installed the CPU monitor to find I'm now using 94% CPU utilisation (still with 45% ethernet).
The time slice has not been changed from default 20%.
I have 1 continuous task (should be a periodic one, but I didn't know enough when I wrote it) and 8 periodic tasks. All the periodic tasks are 100ms and above scan times apart from one which is 50ms (all IO modules have similar scan times to the periodic tasks that they feed).
The largest scan times are averaging about 4ms with a max (1 month since the firmware upgrade) of 10ms.

Everything is working great, just the online browsing is slow.
I increased the time slice (in increments) from 20% to 33% which did not change the average scan times but has helped with the browsing (and saving).

Any comments?
Has anyone else seen this type of thing when upgrading from version 16 to 17?
Is this to do with the add-on instruction I wrote (my first)?
Should I put in a 2nd processor on the system?
Should I increase the time slice until I increase the scan times?

Cheers in advance

I've not seen anything like that going from 16 to 17, on some fairly large programs.
Do explain your periodic tasks though... you have multiple periodic tasks configured for 100ms? I have seen that to be a problem.

A better approach might be to make a single 14.28ms task, and call each of your 100ms tasks once per scan sequentially.

I routinely increase the system overhead timeslice to 32% on all large systems. On some, I even increase the allocated communications buffers.

Do try this though, sometimes it's necessary if the actual processor utilization seems to skyrocket:

Save the current program as an L5K file.
Open the L5K file as a new project, and then download that to the processor.

To be honest I usually set my overhead timeslice to a minimum of 30% and try to be at 40-45% to handle all the overhead communications (i.e. online, hmi comms, etc.). The other thing to check in v17 is to check the radio button Reserve unused timeslice for system tasks. Otherwise the program will keep running the continuous task.

Periodic tasks. The scan rate is taken from Logix5000 Task Monitor
DCS - 250ms period - 2ms scan rate
DCS_PID - 200ms period - 2ms scan rate
Drives_Alarms - 250ms period - 2ms scan rate
HD_Cleaners - 250ms period - 2ms scan rate
Drives_Analogue - 50ms period - 4ms scan rate - 65% CPU Utilisation

I higlighted the Drives_Analogue as that uses 65% of the CPU utilisation with the other main component being the communications at 25% (with time slice at 33%). This task co-ordinates the speed of the 16 drives in our system, which is why it is run so fast.

The reserveunused timeslice for system tasks.
I am using a continuous task so what would happen if I enable this?

My continuous task is the start/stop/interlocks for the drives. At the next shutdown I will change this to a periodic task (probably 100ms) then I will not have any continuous tasks therefore the time slice would not be used.
I currently have no overlap on any of my periodic task, which is good.

From my reading, if I increase the time slice, all that this will do is reduce the amount of time given to the continuous task compared to the background task (comms, etc) without affecting the periodic tasks.

Am I correct on this?

Honestly, I don't know that I see a problem there, unless you are missing interrupt fires.

Why bother putting control logic into a periodic task?
The cyclical task is interrupted at need to service the periodic ones, so you won't be actually 'saving' anything.

rdrast, thats a fair point.
Everything is working great, I just got scared with the CPU Utilisation being so high and thinking I might lose something.

Increasing the time slice (now at 50%) has made browsing online alot smoother so a HUGE thank you for everyones advice.

Next shutdown I will do the L5K thing to download the program

Clx cpu usage

There has been an update to the task manager program, go to downloads to get it. This should fix the problem with it reading processor usage incorrectly high.