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Implementing the zIIP Specialty Processor

IBM has introduced the zIIP Specialty Processor, a CPU engine, for the z9 and z10 hardware systems. The zIIP processor, like its predecessors, the IFL and zAAP processors, can be added to a hardware box without increasing the MIPS rating of that hardware operating environment. Many software license fees are based on the MIPS rating of the hardware, but the specialty processor allows you to increase the processing power of the hardware without increasing the MIPS rating and therefore without increasing the MIPS-based license fees.

Unlike the IFL and the zAAP processor, the zIIP processor allows certain existing z/OS workloads to be executed on the zIIP processor. For these workloads to execute on the zIIP processor, they must be executed as a Work Load Managed (WLM) Enclave SRB.

The SMP processing covered in the section titled Implement Symmetrical Multi-Processing can be changed from a main task TCB with additional TCBs for request processing to a main task TCB and WLM Enclave SRB/TCB pair for request processing. This enhancement allows portions of the existing CA Datacom workloads to be available for off-loading to available zIIP processors. The TCB of the SRB/TCB pair is used to process those parts of the workload not available for execution on the SRB.

Business Value

For sites with zIIP processors, this ability allows you to offload portions of the MUF workload to the zIIP processor which could free up the General Purpose (GP) processors for other workloads. By freeing up GP processors, you can run additional workloads or possibly delay a planned increase to the GP processor capacity.

Additional Considerations

Sites with minimal MUF workloads should not use SMP processing as it incurs additional overhead required for parallel task locking that is not going to be useful unless multiple task processing is occurring.

Sites that do not have a zIIP processor would not typically benefit from WLM Enclave SRB processing.

WLM Enclave SRB processing is implemented in the MUF by specifying the startup option SMPTASK with the additional tcborsrb parameter.

SMPTASK maxtcb,currenttcb,readytorun,tcborsrb  
tcborsrb

Defaults to TCB which is the standard processing mode for r11 (and before). Changing the specification to SRB tells the MUF to convert from multiple TCB processing to the WLM Enclave SRB/TCB pair processing.

For sites that want the MUF to take advantage of zIIP processors, but want to limit the amount of the workload that is offloaded, the MUF startup option ZIIP_USER_LIMIT can be specified. Typically this limit would only be implemented for test systems where you want to use zIIP processors for some processing but also keep the test systems from putting a significant load on the zIIP processor.

For more information about using zIIP processing, see the CA Datacom/DB Database and System Administration Guide.

If you want to estimate the amount of workload that could be offloaded even though you do not have an available zIIP processor, you should implement the SMPTASK parameter with the SRB specification. Even though the SRBs are not dispatched to a zIIP processor, the MUF provides statistics on the amount of workload that would have been dispatched if the zIIP was available.