In the IBM Z Common Data Provider Version 2.1.0, the System Data Engine (SDE) makes improvement on the zIIP offload function. The System Data Engine can now offload more work to zIIPs and at the same time reduce the additional overhead incurred.
Performance improvement when activating the zIIP offloading function
When the zIIP offload function is enabled, the System Data Engine code offloads as much eligible work as possible to zIIP processors to minimize the MIPS consumption on general processors (GCPs).
In the performance measurements conducted in our lab, we saw that 99% or more of the SDE CPU time was eligible to be off-loaded to zIIPs. And when combined with the Data Streamer, in the performance measurements conducted in our lab, we saw that 96% or more of the combination of SDE and Data Streamer was eligible to be off-loaded to zIIPs. Actual percentage off-loaded to zIIPs may be considerably less, depending on the number and availability of the zIIPs in the environment, as well as other environmental factors. Because of processing overhead associated with off-loading work to a zIIP, the realized reduction in GCP usage will likely be lower than the zIIP off-load percentage.
Things to consider before activating the zIIP offloading function
Before using zIIP processors, consider the performance impact of activating the zIIP offloading function.
Offloading work to zIIP processors adds additional overhead in CPU time. You will discover that the total CPU time (GCPs + zIIPs) when zIIP offloading is enabled is slightly higher than the total CPU time on GCPs when zIIP offloading is not enabled.
Make sure you have enough capacity on zIIP processors. z/OS may redirect zIIP eligible work to general CPUs when all zIIPs are busy. If your system is consistently in shortage of zIIP resources, the additional (overhead) CPU time to use zIIP processors can overwhelm the CPU time that is offloaded to zIIP processors. In the worst case, the general CPU usage may be even increased.
Activating the zIIP offloading function
The zIIP offloading function is disabled by default. To activate the zIIP offloading function, specify ZIIPOFFLOAD=YES in the PARM parameter in the EXEC statement of the System Data Engine started task procedure or batch job JCL as shown in the following example.
//HBOSMFCL EXEC PGM=HBOPDE, REGION=0M,TIME=1440,
// PARM=’SHOWINPUT=NO,ZIIPOFFLOAD=YES‘
For additional information on what’s new in IBM Z Common Data Provider Version 2.1.0 see https://www.ibm.com/support/knowledgecenter/SSGE3R_2.1.0/cdp_v210.html
For additional information on IBM Z Common Data Provider see http://ibm.biz/CDPzInfo