It is common in today’s challenging business environments to find IT organizations intensely focused on expense reduction. For mainframe departments, this typically results in a high priority expense reduction initiative for IBM Monthly License Charge (MLC) software, which usually represents the single largest line item in their budget.
This article begins a four-part series focusing largely on a topic that has the potential to generate significant cost savings but which has not received the attention it deserves, namely processor cache optimization. The magnitude of the potential opportunity to reduce CPU consumption and thus MLC expense available through optimizing processor cache is unlikely to be realized unless you understand the underlying concepts and have clear visibility into the key metrics in your environment.
Subsequent articles in the series will focus on ways to improve cache efficiency, through optimizing LPAR weights and processor configurations, and finally on the value of additional visibility into the data commonly viewed only through the IBM Sub-Capacity Reporting Tool (SCRT) report. Insights into the potential impact of various tuning actions will be brought to life with data from numerous real-life case studies, gleaned from experience gained from analyzing detailed processor cache data from 45 sites across 5 countries.
Processor cache utilization plays a significant role in CPU consumption for all z processors, but that role is more prominent than ever on z13 and z14 models. Achieving the rated 10% capacity increase on a z13 processor versus its zEC12 predecessor (despite a clock speed that is 10% slower) is very dependent on effective utilization of processor cache. This article will begin by introducing the key processor cache concepts and metrics that are essential for understanding the vital role processor cache plays in CPU consumption.