The HiperDispatch state of the system is determined by the number of logical processors defined on an LPAR and the HIPERDISPATCH=YES|NO keyword in the IEAOPTxx member of SYS1.PARMLIB.
All partitions with more than 64 logical processors defined at IPL are forced to run with HIPERDISPATCH=YES. LPARs with more than 64 logical processors defined are also unable to switch into HIPERDISPATCH=NO after IPL.
For all partitions with less than 64 logical processors, HiperDispatch is enabled or disabled by the HIPERDISPATCH=YES|NO keyword in parmlib member IEAOPTxx. This parameter can be changed dynamically with the use of the SET OPT command. This enables the operating system to choose the desired mode of operation.
When a new hardware generation is installed, for any z/OS® image(s) that are running with HiperDispatch disabled, the system programmer should reevaluate whether those z/OS image(s) should be migrated to running with HiperDispatch enabled in the new environment.
On z10™ on any z/OS release, HiperDispatch disabled is the default. However, customers are encouraged to run with HiperDispatch enabled on z10 to take advantage of the processing benefits.
Beginning with z/OS V1R13 on IBM® zEnterprise® 196 (z196), HiperDispatch enabled is the default. With z/OS V1R13 running on a z196, z/OS partitions with share greater than 1.5 physical processors will typically experience improved processor efficiency with HiperDispatch enabled. z/OS partitions with share less than 1.5 physical processors typically do not receive a detectable performance improvement with HiperDispatch enabled, but IBM recommends running those LPARs with HiperDispatch enabled when the performance improvement is greater than or equal to HiperDispatch disabled.
There are no new hardware controls or settings to enable use of HiperDispatch within a logical partition; however, the existing “control global performance data” security setting must be enabled on HMC for proper operation of HiperDispatch in a logical partition. HiperDispatch cannot effectively utilize vertical low processors when other partitions are active on the system and “global performance data” is not enabled.
For further information about the HIPERDISPATCH parameter, refer to z/OS MVS Initialization and Tuning Reference.