Gary_Cherlet

Increased CPU Costs using MT and zIIP

Discussion created by Gary_Cherlet on Mar 7, 2011
Latest reply on Mar 7, 2011 by TomFromObjEx
Hello All:
I have a client with 12 IDMS regions, after installing IDMS 17.0 SP1 with all APAR's applied on top of SP1 and turning on zIIP we noticed a very large increase in CPU costs associated with the new release of IDMS. Here is an explanation from my client on how they found a resolution to this issue:

We confirmed that the large increase was due to the combination of MT and zIIP. The usage did go down after turning off MT but there was still an unacceptable increase because of zIIP. We checked the KOMAND billing and didn't find any errors.

After discussions with CA high level support (John Siraco), we confirmed that the zIIP portion of the increase is because there is some overhead on the main CP for the zIIP offload (it uses enclave SRB mode and has to do a lot of switching). Since we were billing for total CPU (normalized zIIP + main CPU time), we were getting an actual increase because of this zIIP offload overhead.

We should actually not be billing for zIIP CPU (or at least bill at a lower rate), since there is no associated software cost. So, we will be changing the Billing formula to not charge for the zIIP CPU. It is simply not correct to bill zIIP CPU at the same rate (faster, cheaper processor).Our Billing person is currently in the process of re-running the Billing beginning with last June using the new formula. We will be issuing credits for the difference and will also be calculating an average to credit them for the portion of the increase due to MT being on from June thru mid-November.

It was actually good that MT was turned on since that made it stick out like a sore thumb, enabling us to do this entire discovery about the zIIP overhead. This may be something you might want to ensure your other customers are aware of.

William M. Allen, Jr.

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