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ibi™ Open Data Hub for Mainframe Connectors 1.0.8

# Enabling Use of the zIIP Specialty Engine

If your site has a zIIP (System z Integrated Information Processor) specialty engine from IBM, you can offload specific categories of workload from the Central Processors to the zIIP.

The zIIP engine is a restricted version of a Central Processor (CP), also referred to as a General Processor (GP). The capacity of the zIIP engine does not count toward the overall MIPS rating of the mainframe image, so the CPU usage incurred on the zIIP is effectively free. Central Processors are often configured to run at speeds below their maximum rating for cost saving and capacity planning purposes. For Central Processors, 100% capacity typically refers to the maximum MIPS that the processor is allowed to generate at that installation, in accordance with your contract with IBM. In contrast, the zIIP engine always runs at true 100 percent of capacity.

As much as 80 percent of server processing is enabled to run on the zIIP engine. Typical workloads are expected to offload 30 to 80 percent of CPU processing to the zIIP engine.

To make use of the zIIP enablement feature, the server must run in an authorized state.

## What Is a zIIP Specialty Engine?

Though physically identical to a Central Processor, the zIIP engine is microcoded during installation to run specific types of workloads. The Central Processor continues to handle the operating system, I/O interrupts and timer interrupts, job initiations, and user interactions with the operating system. The zIIP concentrates on CPU intensive workloads, leaving the Central Processor more time to absorb otherwise queued workloads, thereby achieving some overall performance improvement across all mainframe activity.

## Steps to zIIP Enablement

This section describes steps and requirements for the server use of the zIIP processor.

The steps to server zIIP enablement are:

1. Obtain APF authorization for the server load library.
2. Activate the zIIP feature using the `SET ZIIP=ON` or `SET ZIIP=ON/SIMMAXZIIP` command. For instructions, see Activating a zIIP Environment or Projecting zIIP Usage.

### Usage Notes for Use of the zIIP Processor

- Maximize the blocksizes of data sources that are read or written by the server to reduce the number of I/Os required to access the file. This reduces the number of switches to non-zIIP mode that the server agents have to make, thus permitting a greater percentage of zIIP contribution to the request.
- Move or rewrite functions developed at your site since the server must switch to non-zIIP mode for each call to such routines. You may be able to use one of the following possible solutions:
  - Move the routines from DEFINEs to COMPUTEs to reduce the number of times they are referenced. This tactic must be applied carefully, and only when report results would not change.
  - Rewrite the routines using DEFINE FUNCTION, which executes on the zIIP processor.
  - Confine the routine to a pre-step run with `ZIIP=OFF` which collects its calculated results, then use those calculations in the next step with ZIIP=ON.

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