zIIP Processing

The VTE zIIP support allows most of the VTE CPU intensive work to be zIIP-eligible, that is, eligible to be dispatched on (or offloaded to) zIIP processor(s). This intensive CPU work includes general data moves, all types of compression and other internal tasks (like addresses translation).

This capability is enabled provided the following is true:
  • The CPC machine supports zIIP.
  • The system level supports zIIP.
  • The host has at least one online zIIP processor.
  • No zIIP processors are available, but the z/OS capacity planning projection for zIIP processor(s) is enabled (PROJECTCPU=YES in IEAOPTxx member), in which case the projected CPU is accumulated as zIIP on CP time.

When the zIIP processor(s) are available and all scheduled work can be dispatched on them, as much as 97% of the VTE server work is offloaded from the CP processor(s).

Note: Due to the special processing required by the zIIP processor(s) (i.e. managing enclave SRBs), the total consumed CPU (i.e. CP + zIIP) slightly increases.
The following table depicts an estimation of work percentage that is offloaded from the CP processor(s) to the zIIP processor(s) when virtual tapes are written using the various compression algorithms.
Note: The estimated offloaded work results depend on the compression ratio and were obtained using a mix of full disk backup jobs and various application jobs.
Table 1. Compression algorithms and CPU savings
Compression Type CPU % Savings
(0,0) 6
(1,1) 76
(2,1) 97
(3,1) 62

The read results vary and depend on the compression ratio results. The better the compression ratio is, the more percentage of workload is offloaded to the zIIP processor(s).

The amount of offloaded work is displayed for each accessed virtual tape in the HVT023I message and is updated in the VTE SMF record.

Note: The zIIP support is not available for VTE offline utilities (like HVTUV2V) or to utilities that use the VTE Access Method (VAM) to access virtual tapes.