IBM z Systems Integrated Information Processors (zIIP) have been around for many years. Companies benefit when software vendors, like Alebra Technologies, offload processing to zIIPs to save on software charges which are based on processor usage. The amount of benefit is greatly impacted by the design strategy that your software vendors use when exploiting the zIIP.
I’ll spare you the potentially mind-numbing details of hardware caching algorithms and the details of the z/OS Dispatcher and reduce it to these simple factors:
- There are strict rules that code must observe in order to run on a zIIP.
- Many z/OS-provided functions cannot run on a zIIP.
- There is a very significant overhead cost associated with switching back and forth between zIIP and non-zIIP processing.
In initial tests cases run by Alebra, we found that the overhead to switch between general purpose engines and zIIP engines was larger than we anticipated, even when using the most efficient methods available. Some tests showed higher processor usage with zIIP than without – a negative impact. Moving compute intensive work such as compression or encryption might yield positive results, but nowhere near the levels we desired. Our conclusion was that in order to benefit from the use of zIIPs, the entire application (or as much as possible) had to execute on the zIIP.
Alebra’s delivered implementation executes the core application – the movement of data and all processing associated with it in the zIIP. Once data transfer begins, PDM code runs in the zIIP except for infrequent special case events (checkpoints, EOV processing). For small transfers, displays which show CPU time in seconds with two decimal places typically show no CPU time (less than 1 centisecond). Larger transfers only show a small fraction of a CPU second. CPU saving are huge!
Customers should be cautious about software vendor claims regarding zIIP exploitation. Implementation methods, and consequently the results, can vary greatly. Alebra’s approach reduces the remaining CPU time on general purpose processors to the point where it is barely measurable. A BIG win for our customers.
Bill Yeager | Chief Technology Officer | email@example.com