Re: jobs running in one subsystem take up more CPU then rest of jobs

Disk suffers at 40%+ arm utilization but I don't recall anything about CPU.
40% is an old number - more than a decade old - but I've not heard anything
about it changing with the newer disks & controllers. In essence if the
arms are that busy the controller cache is probably working pretty hard as
well or the job characteristics simply make cache less helpful.

Now, if you frequently run the CPU at 100% (or max CPU in an uncapped LPAR
environment) you may want to start looking at performance data to see if
latencies/delays are occurring but in general there's nothing wrong with
100% CPU usage.

BTW some CPU (and disk) is used swapping jobs in & out of memory so the
solution might not be more CPU .. it could be more RAM or simply tuning the
number of concurrent jobs. That's why CPW rating always assumed a machine
with max (or nearly so) RAM and lots of disks.

Performance management is a big "it depends" .. there's rarely a
one-size-fits-all answer.

On Thu, Nov 19, 2009 at 10:50 AM, Kirk Goins <kgoins@xxxxxxxxxxx> wrote:

Charles Wilt wrote:

John,

If the users aren't complaining and the total CPU usage is less than
100%, then don't worry about how much the batch jobs are taking.

Look at it this way, if the CPU isn't 100%, then part of the time your
system is doing nothing....so how much did you pay for that
paperweight anyway? :) Theoretically, you want the system to run at
95% or so all day long. Of course in real life, you've got workload
peaks & valleys, plus you want room for growth so you're not upgrading
every week.

The point is, why would you want to constrain the work being done for no

reason?

Charles

Charles,

Sometime ago ( might need a 'WAY-BACK' Machine ) IBM used to tell us
that running a CPU over 60% would start to cause performance problems
with in the CPU. I don't remember the terms ( reason ) they gave but
something like thrashing if if was a disk comes to mind. The Higher and
Longer it ran that way the less real work was done. Anyone remember
anything like this?

Maybe it was a Dream wishing for more horsepower :)


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