Memory Hierarchy On The Z13S One Cpc Drawer System (Two Nodes); Relative Nest Intensity - IBM z13s Technical Manual

Figure 12-2 shows a memory nest in a z13s single CPC drawer system with two nodes.
Figure 12-2 Memory hierarchy on the z13s one CPC drawer system (two nodes)
Workload capacity performance is sensitive to how deep into the memory hierarchy the
processor must go to retrieve the workload instructions and data for running. The best
performance occurs when the instructions and data are in the caches nearest the processor.
In this configuration, little time is spent waiting before the task runs. If the instructions and
data must be retrieved from farther out in the hierarchy, the processor spends more time
waiting for their arrival.
As workloads are moved between processors with various memory hierarchy designs,
performance varies because the average time to retrieve instructions and data from within the
memory hierarchy varies. Additionally, when on a processor, this component continues to
vary. This variation is because the location of a workload's instructions and data within the
memory hierarchy is affected by many factors that include, but are not limited to, these
factors:
Locality of reference
I/O rate
Competition from other applications and LPARs

12.4 Relative nest intensity

The most performance-sensitive area of the memory hierarchy is the activity to the memory
nest, which is the distribution of activity to the shared caches and memory. The term Relative
Nest Intensity (RNI) indicates the level of activity to this part of the memory hierarchy. Using
data from CPU MF, the RNI of the workload running in an LPAR can be calculated. The higher
the RNI, the deeper into the memory hierarchy the processor must go to retrieve the
instructions and data for that workload.
Chapter 12. Performance
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