XCOM capability to offload workload onto zIIP Processors
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XCOM capability to offload workload onto zIIP Processors


Article ID: 9362


Updated On:


XCOM Data Transport XCOM Data Transport - z/OS XCOM Data Transport - Linux PC XCOM Data Transport - Windows


This document summarizes the new zIIP Support feature for XCOM Data Transport, the new parameters introduced to support it, requirements to use it and answers a few basic questions about it.


Component: XCOM Data Transport for z/OS


What is zIIP?
In IBM System z9 (and later) mainframes, the System z Integrated Information Processor is a special purpose processor. zIIP is intended to free up general computing capacity and lower the overall cost of computing for CPU intensive workloads.

What workloads are offloaded?
Initially, data compression and decompression functions are offloaded to zIIP when available and feasible, as they are highly CPU intensive functions.

Why should I use zIIP support?
The goal of utilizing zIIP is to reduce CPU utilization and the costs that are associated with that utilization. Given that data compression accounts for a significant portion of CPU utilization for a data transfer, moving this processing to a zIIP reduces utilization and costs.

What are the requirements for using zIIP Support?

  • Any supported version of CA Common Services for z/OS 

  • The Common Services library must be available to the XCOM Server started task or XCOMJOB TYPE=EXECUTE job.

  • XCOM requires that the size of the data block being compressed or de-compressed is a minimum of 4096 (4K) bytes. This minimum size is to insure that the overhead of switching the workload to the zIIP does not affect the performance of the transfer.

  • We recommend that the configuration parameter MAXPACK is set to a minimum of 4096. The higher the value for these parameters, the more efficient it is to use zIIP.

  • For any transfer, PACK=LENGTH is specified to insure that the 4K minimum size for compression on the zIIP is realized. Without this parameter, the record size of data in a file would need to be 4K to move the compression workload to the zIIP.

What new parameters have been added for zIIP support?
By default, XCOM uses zIIP support automatically providing that the zIIP Enablement Service is available to load.

  • A new PARM and configuration parameter can be specified to disable the zIIP support. The parameter is

    ZIIP=YES|NO (YES is the default)

  • New modify commands for the XCOM Data Transport Server have been provided to report on status and allow zIIP support to be enabled/disabled.

    provides information about which CPUs (standard and zIIP) are defined and online. It also displays the status of zIIP support and statistics which show the total amount of processing time that was eligible to run on zIIP and that executed on zIIP.

  • ZIIP,ENABLE and ZIIP,DISABLE commands allow an administrator to enable or disable the zIIP support for future data transfers.

  • The output of the SHOW command for a specific transfer has been enhanced to display the current zIIP CPU eligibility and utilization times.

What facilities are available to monitor zIIP usage?
The ZIIP STATUS modify command is automatically issued on startup and termination of the XCOM Server and XCOMJOB TYPE=EXECUTE job start and termination.

For each transfer, statistics about CPU and zIIP usage are written into the history record and SMF record. This data can then be reported on through a TYPE=HISTORY job and/or supplied CA Easytrieve reports.

Additional Information

XCOM doesn't support offloading SSL processing to zIIP.  Even then, zIIP is only used if there is no zEDC present on the system, and the user is not using a ZLIB compression algorithm.

The XCOM SSL processing uses LE/C which makes it incompatible with using zIIP.  There are certain SSL algorithms that can use ICSF (a hardware-based encryption processor add-on) for encryption.  This offloads encryption processing from being software-based and thereby uses less CPU.

ICSF usage is automatic when certain algorithms are used by System SSL.