Other articles have previously described the System z Application Assist Processor (zAAP) and System z Integrated Information Processor (zIIP) engines and the capabilities they provide. This article describes how to analyze the impact of these engines on your software charges and answer three key questions:
• If zAAP and/or zIIP engines are added to your environment, how will your software charges be reduced?
• If you already have these engines installed in your environment, how will they reduce your software charges?
• Would additional engines provide additional value?
The actual work executed on these engines, and the eligible work that could be executed, can be used to study possible changes in Logical Partitions (LPARs). That can lead to estimating the simultaneous 4-Hour Rolling Average (4HRA) across the LPARs of a machine. Finally, the change in software charges can be estimated.
zAAP engines were announced for the z990 machines to offload Java from the general-purpose engines. zAAP support was introduced with z/OS V1R6. As a component of recording information about zAAP engines, z/OS records work that’s executing on the zAAP, and work that’s running on a standard Central Processor (CP) that could have run on a zAAP. All processors/machines announced since the z990 also support zAAPs.
zIIP engines are available on z9 BC, z9 EC, z10 EC, and z10 BC processors initially to offload specific types of DB2 work. Other types of work now run on zAAP and zIIP engines, but won’t be covered here.
Both engines offer a lower initial cost and lower ongoing maintenance costs than general-purpose engines. zXXP capacity isn’t included in IBM’s announced Millions of Service Units (MSU) values for machines. zXXP CPU time isn’t included in an LPAR’s 4HRA; there are no software charges for zXXP capacity. There is some additional overhead to determine which work is zXXP-eligible and to handle the dispatching. However, that’s a small price to pay when there are no software charges for the capacity of these engines.
There were some early zAAP estimation techniques, but they aren’t required today. IBM added “PROJECTCPU” as an option in PARMLIB member IEAOPTxx to allow estimating of both zAAP and zIIP information without having the engines installed. The PROJECTCPU control replaces the -Xifa:force control for zAAP. zIIP and PROJECTCPU are supported in z/OS V1R8, or in z/OS V1R6 and V1R7 via maintenance. PROJECTCPU allows a site to collect the “eligible” time before a zXXP is even installed. Of course, you still need applications that will use the zXXP to have information to collect. This would include Java, DB2 V8, DB2 9, appropriate levels of z/OS, and some Independent Software Vendor (ISV) products.
The purpose of zXXP is to move CPU usage off the general-purpose engines to the zXXP. Since there are no software charges for CPU usage on zXXPs, moving work off the general-purpose engines may lower the 4HRAs in your LPARs. Moreover, zXXP usage also may lower the maximum simultaneous 4HRAs. If your billable MSUs are driven by an overnight batch workload, and adding zXXP engines will primarily help your daytime online workload, then there may not be a reduction in monthly software charges.