Allow zIIP Eligible CPU tasks to utilize unentitled (Vertical LOW CPs) , when zIIPs need help.

Currently, only entitled (Vertical High and Medium) CP's can help zIIP s when the zIIPs are near 100% utilization. VERTICAL LOW CPs are not entitled to help with zIIP eligible work when the zIIPs need help. Most LPARs are configured a percentage of extra CPs, that are not entitled, to allow the system to utilize unused, available CP capacity for unforeseen or unusual CPU demand. Should the zIIP eligible CPU demand have similar increases, this available, unused CP capacity cannot be utilized.

We discovered this in IBM case TS016638086. After the IPL of Application Development (test) systems, that have a large number of Webspheres, zIIP Boost was activated. The zIIPs were 100% utilized and the CP's were 30% utilized. The recovery of all the WebSpheres extended beyond the 1 hour Boost period. If the unentitled CP's could be utilized to help the zIIPs, the elapse time to recover all the WebSpheres would have been significantly reduced. It should also be considered that most scheduled IPL’s occur during off business hours when CEC CPU utilization is low and there is a significant amount of CPU capacity available.

As a part of our research in IBM case TS016638086, after the IPL of a test system while zIIP Boost and Speed Boost were active, we configured the zIIP offline and all the CP’s (entitled and unentitled) approached 100% utilization. We considered disabling zIIP Boost after IPL’s or configuring zIIPs offline after every IPL, but this could be inefficient use of our zIIP capacity.

This idea would help insure the all of the available CPU capacity can be utilized to satisfy the demand.