Guest dispatching metrics

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The z/VM® Performance Toolkit report USTAT (FCX114, Wait State Analysis by User) can be used as a first approach for identifying guest wait states. However, the interpretation of this report requires some caution.

One aspect of report USTAT is that the reported percentages are percent of samples collected, not the percent of time spent in the various states. For more accuracy we therefore used the new dispatch delay time accumulators provided by the z13 exploitation SPE. These report the dispatch wait time - the amount of time (microseconds μs) that passes between the instant the virtual CPU becomes ready to use a logical CPU, and the instant the z/VM Control Program dispatches it.

The new dispatch wait delay time accumulators can be found in the CP Monitor D4 R3 record, MRUSEACT, fields USEACT_CALDWDCT and so on, which is documented at:

https://www.vm.ibm.com/pubs/mon630/MRUSEACT.HTML

This seems to be much more appropriate for determining the effects we wish to show in this study.