Offload workload to zIIP processors

IMS HP Image Copy supports the IBM® System z® Integrated Information Processor (zIIP) to offload eligible database workloads to zIIP processors.

Data compression and decompression is one of the most CPU-intensive workloads in IMS HP Image Copy processes. By enabling the zIIP support with the ZIIPMODE keyword, you can use zIIP processors to run the data compression and decompression workloads.

You can enable zIIP processors by the following specifications:

  • For the Image Copy function, the workload to create compressed image copies is run by zIIP processors if both ZIIPMODE=COND and COMP=Y are specified.
  • For the Recovery function, the workload to read compressed image copies is run by zIIP processors if ZIIPMODE=COND is specified.
  • For the Create Image Copy function, the workload to read compressed image copies is run by zIIP processors if ZIIPMODE=COND is specified. The workload to create compressed image copies is also run by zIIP processors if both ZIIPMODE=COND and COMP=Y are specified.

The CPU time consumed on zIIP processors is notified by message FABJ0426I.

Requirements: The following requirements must be met to enable zIIP processors:
  • The SGLXLOAD library of IMS Tools Base is added to the STEPLIB DD statement of the IMS HP Image Copy JCL.
  • The SGLXLOAD library is APF-authorized.

Considerations before using zIIP processors

Before using zIIP processors, consider and estimate the performance impact of using zIIP processors:

  • Using zIIP processors to run eligible workload requires overhead, especially in elapsed time of the job. If you use zIIP processors, you must test the performance impact in the test system before using them in the production system.
  • If you enable parallel image copy by specifying the AIC ICEIN statement, you might need to consider the number of zIIP processors that are available. If the number of zIIP processors is considerably less than the number of CPs (main processors), you might see significant performance degradation because the workloads run by the zIIP processors (compression processing) is CPU-intensive, and a small number of zIIP processors causes resource contention.
  • Using zIIP processors requires overhead in CPU time. Therefore, the use of zIIP processors is beneficial only if the amount of offloaded CPU time is larger than the amount of overhead CPU time. When both of the following conditions are true, specifying ZIIPMODE=COND, in many cases, results in an increase in CPU time:
    • Image copies are created on tape volumes, such as by using the STACK keyword
    • IDRC is enabled on a tape subsystem
    Under these conditions, the amount of CPU time consumed for the compression routine is not large because compression process is mostly done by hardware, not software. Therefore, the amount of CPU time that is offloaded to zIIP processors is quite small. The additional (overhead) CPU time to use zIIP processors can overwhelm the CPU time that is offloaded to zIIP processors.