Re: CPU utilization, Priority, and Throughput

[watern@xxxxxxxxxxxxxx]

Hi Richard,

you wrote... ...
<snip> ..  a  workaround recommendation arose for the "UBEs hog the CPU" problem
- change the time slice to 200 milliseconds.  It helps but it isn't a cure.
<endsnip>..

Strangly enough, this is exactly the strategy that I remember being adopted in
the case I described, as recommended by a performance tuning expert who I am
sure was brought in from IBM to advise.

What actually happened was I developed this application out of hours, mostly
weekends, and so was normally the only user signed on to the machine for most of
the time that it was being developed. During my testing I didnt notice any
performance problems at all !!   I completed my work one weekend, and at 9:20am
on the first Monday that testing took place, I got a frantic phone call saying
that when the route-planner was running the system seemed to completely hang.

IBM were called in to advise and my understanding of their explanation was as I
described previously.

There recommendation was.. when the job is about to become cpu-bound - change
the timeslice to 200ms, and lower the job priority to 51. More or less just as
you described above !  Their reasoning as I remember it was that this would mean
that the route-planner would take all the available resource, but would give
plenty of opportunity for other jobs to grab the CPU whenever they needed it.

This was back in 1991/92 so that is why I mentioned that it may no longer be the
case - with all the advances since then I would not be at all surprised if
something was done about this behaviour at some point. I dont remember hearing
about a pre-emptive feature of the AS400 job despatcher at that time and that
would go against what we were experiencing then.

The approach suggested by the performance expert was adopted and worked very
well.

It is interesting to hear of your similar experience.. I hope that someone may
be able to confirm how the work management function handles this scenario now,
in the year 2000!

Rgds,
Nigel


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