Re: Recommended CPU % utilized

["R. Bruce Hoffman, Jr." <rbruceh@xxxxxxx>]

Pete Hall wrote:
> 
> What indicators can be used to justify or shoot down a proposal to upgrade
> CPU? Are there any published recommendations anywhere? Digging through the
> work management guide didn't turn up anything. About all I could come up
> with is a bar chart that shows the percent of time that CPU utilization was
> above x%. Subjectively, I know that when it goes over 90%, interactive
> response starts to deteriorate, and since we have tuned batch to favor
> interactive response time, I suspect that batch starts to deteriorate as
> soon as utilization gets over 50-60%, with major throughput degradation by
> the time it reaches 80%. I have not done any benchmarks on this yet. That's
> my probable next step.
> 

What you are asking is more complicated than you might expect. When it
comes to CPU upgrades, you are really looking for the amount of time
that processes must WAIT to get the CPU and then remove the IO waits
from the equation.

If you don't have the performance tools LP, then determination yea or
nea will be purely subjective.

If you have the tools, then you need to monitor around the time of heavy
CPU use and then look in the reports for the jobs waiting for CPU. This
is based on "Queueing Theory" and, if I remember correctly, there is an
appendix for that topic in the Performance Guide.

Actually modelling the performance, verifying the model and then
upgrading the CPU in the Performance Tools is the best way to do this
and is one of the reasons that everyone with an AS/400 that COULD grow
should be running regular collections (and I don't mean the PM/400
Marketing junk).

You should know the batch/interactive workload mix, the peak utilization
rates of disk, IO and CPU based on time of year and time of week, all
off the top of your head. If you run the tools regularly, produce the
summary reports weekly and spend an hour each week quickly reviewing
them, you can do this. Then the question you are asking is only one or
two monitor sessions and three or four hours of modelling work away.

The preceeding has been an editorial.

good luck.
-- 
===========================================================
R. Bruce Hoffman, Jr.
 -- IBM Certified AS/400 Professional System Administrator
 -- IBM Certified AS/400 Professional Network Administrator

"The sum of all human knowledge is a fixed constant.
    It's the population that keeps growing!"
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