In the IBM Common Data Provider for z Systems 2Q19 continuous delivery PTFs, the System Data Engine (SDE) is enhanced to offload eligible work from general purpose processors to zIIP processors. The zIIP exploitation helps customers reduce their total cost of ownership (TCO).
Performance improvement when activating the zIIP offloading function
The System Data Engine code is reconstructed to offload as much eligible work as possible to zIIP processors to minimize the MIPS consumption on GCPs.
In the performance measurements conducted in our lab, we saw that 82% or more of the SDE CPU time was eligible to be off-loaded to a zIIP. And when combined with the Data Streamer, in the performance measurements conducted in our lab, we saw that 84% or more of the combination of SDE and DS was eligible to be off-loaded to a zIIP. Actual percentage off-loaded to zIIP 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 zlIP processors, consider the performance impact of activating the zIIP offloading function.
Offloading work to zlIP processors adds additional overhead in CPU time. You will discover that the total CPU time (GCPs + zIIPs) when zIIP offloading is enabled is 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 zlIP processors can overwhelm the CPU time that is offloaded to zlIP 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‘
Looking ahead
IBM has development work in progress to offload more work in System Data Engine to zIIP processors. While converting more code to be zIIP eligible, the System Data Engine can offload more work to zIIPs and in the meanwhile reduce the additional overhead incurred.
For additional information on what’s new in the CDPz 2Q 2019 PTF see https://www.ibm.com/support/knowledgecenter/SSGE3R_1.1.0/cdp_v110.html
For additional information on IBM Common Data Provider for z Systems see http://ibm.biz/CDPzInfo