But would you really expect an effect of more than a few percentage
points in the efficiency of one CP from only going from 3 to 4 engines?
If you are seeing a large difference in run time, perhaps you should
also look for an explanation that can produce a much larger difference
than the MP effect. Maybe by removing a CPU bottleneck you have moved
your major system constraint elsewhere, either to real memory or to DASD
throughput, or some logical interlock. Perhaps the longer running jobs
are now doing significant paging because of greater contention for real
memory, or are having to wait on physical I/O to DASD more -- because
other things that used to be too starved for CPU to compete are now
running and using resources other than CPU that used to be more
plentiful in a CPU-starved environment.
JC Ewing
On 02/09/2012 12:04 PM, Hal Merritt wrote:
I suppose that is reasonable for a single threaded, CPU bound job as a little
is lost from each engine as another is added. However, you should be able to
run more concurrent work giving a better over all through put.
Another benefit of another engine is that, if not needed for anything else,
z/os likes to direct I/O interupts to just one engine. This allows the other
engines run a little smoother and again should increase your overall thoughput.
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of
gsg
Sent: Thursday, February 09, 2012 10:39 AM
To: [email protected]
Subject: Turning on additional CPs
We have a z10 with 4 engines. Since upgrading to this box, we were only
running 3 engines. However, we recently turned on the 4th engine. We noticed
that several jobs started running longer, which we didn't expect. Could
turning on additional engines actually make a job run longer?
Also, where can I find any read material on the affect of turning on/off
engines.
TIA
...
--
Joel C. Ewing, Bentonville, AR [email protected]
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