z⁄VM Education - Unit 13 - What's going wrong? - LPAR Weights

In my job I often look at MONWRITE data from customer systems. Recently I have seen a rash of data showing me CPCs where the LPAR weights were not set correctly. The consequences were less-than-optimal configurations and in some cases just plain poor operation. In this presentation I review basic concepts about LPAR weight, the notion of entitlement, how to recognize configuration problems, and how to correct them. I also point out some techniques, tools, and references that might help.

FAQ: Q: Once you do your entitlement calculations, can you make your changes, get what you need and move on? A: Managing weights is a continuous investment. Workloads on an LPAR are continuously changing. There are some clients where you can go to a partition and it’s 425% busy every day and all partitions are like that. They have constant core utilizations. In that case, you won't have to change often. For more fluid workloads, maybe today LPAR 6 is hot, tomorrow LPAR 9 is hot and next Wednesday LPAR 2 is hot. It behooves us to pay attention to those changes and manage the weights accordingly.

Q: Does this mean we should do some reports, see what it’s showing, and make changes as often as possible? A: You should do your reports and make changes as often as indicated. The data will tell you what to do. All data is good data.

Chapters: 0:00 - Introduction 1:25 - Basic concepts 12:06 - Ways things go wrong 32:53 - Tools 37:21 - Summary

References: Topics in LPAR Performance - https://www.vm.ibm.com/library/presentations/lparperf.pdf

Brian's z/VM Performance Best Practices - https://www.vm.ibm.com/perf/tips/bestp.html

Controlling Vertical-Low Logical Cores - https://www.vm.ibm.com/perf/tips/unpark.html

LPAR Entitlement Calculator - https://www.vm.ibm.com/perf/tips/calcent.cgi

Understanding z/VM HiperDispatch - https://www.vm.ibm.com/perf/tips/zvmhd.html

Understanding z/VM CPU Utilization - https://www.vm.ibm.com/perf/tips/lparinfo.html

SMT Vocabulary Tips - https://www.vm.ibm.com/perf/tips/smtvocab.html

CPU Utilization in an SMT World - https://www.vm.ibm.com/perf/tips/smtutil.html

Relevant Books: z/VM 7.2 Performance Toolkit Guide - https://www.vm.ibm.com/library/720pdfs/72630205.pdf z/VM 7.2 Performance Toolkit Reference - https://www.vm.ibm.com/library/720pdfs/72630305.pdf

Presentation: https://www.vm.ibm.com/library/presentations/lparwght.pdf

Special thanks to the Metropolitan VM Users Association (MVMUA) for recording this session.