The processing capacity of mainframe CPCs is expressed in MSUs (Millions of Service Units per Hour). One of the characteristics of a specific CPC model is its MSU capacity. This capacity is indicative of its workload processing capability and is directly related to the number of general-purpose CP engines configured. Each LPAR that is assigned logical CP processors uses some amount of the available CPC MSUs. The MSU capacity of a CPC and of individual LPARs can influence the cost of software licensed to run on LPARs. Some software licensing costs can be lowered by defining a capacity limit for an LPAR. The limit prevents the LPAR from using the full MSU capacity associated with the logical processors assigned to it. The RMFMC4 charts can be used to monitor the normal MSU consumption of LPARs that use general-purpose CP engines, and also to determine the appropriate value to use for a defined capacity limit. The four hour rolling average is helpful because LPARs are allowed to exceed the defined limit, without penalty, as long as the four hour rolling MSU average stays below the defined limit. For example, if the daily MSU usage shown for the LPAR in the top example (PRSMLPNM=’CA31’) is consistent, over time, it means that the limit of 455 MSUs is set too high. A defined capacity limit of about 330 to 340 MSUs is a more appropriate setting for this LPAR—given that the peak four-hour rolling average was 322 MSUs.
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