I have a client who asked me this: We had a hotplug rule in place that was working fine for us it was 'HOTPLUG = "user > 20.0"' We started seeing a performance and one thing we noticed is that some of our servers were switched to using the rule 'HOTPLUG="((1 - CP_ActiveAVG) * onumcpus) < 0.08"'
We didn't think this change would cause as big of a performance difference as we saw. We would like to get an idea as to the performance difference between these 2 rules. The systems in question have intermittent high loads. They would be basically doing nothing and then they get a job and need all the CPU they can get for about 12 to 15 minutes. How big of a performance difference would you expect to see between these rules. My interpretation/questions are this: HOTPLUG "user > 20.0"' will add a CPU if the current CPU user percent is greater than 20. Does this mean that if users are using >20 percent of the CPU(s) attached another CPU will be added to the guest? Is that a low/high number? I guess it depends on the workload. 'HOTPLUG="((1 - CP_ActiveAVG) * onumcpus) < 0.08"' The values of CP_ActiveAVG and CP_idleAVG are between 0 and 1. Therefore, 1 - CP_ActiveAVG is the unused CPU capacity. When multiplied by the number of active CPUs, it is specified in CPUs. When the total unused CPU capacity falls below 8% of a single CPU, a new CPU is added. This text is directly from the IBM manual, as is the actual rule defined. How often do sample rules fit real world workloads? If my analysis is correct, I'd expect the first rule to add a CPU earlier than the second. The first one adds a CPU when user percent is over 20. The second adds a CPU usage is over 92 percent. I may be way off. Thanks! Rob (c) 2024 Ensono, LLC. All rights reserved. Ensono is a trademark of Ensono, LP. The information contained in this communication is confidential, is intended only for the use of the recipient named above, and may be legally privileged. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please resend this communication to the sender and delete the original message or any copy of it from your computer system. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www2.marist.edu/htbin/wlvindex?LINUX-390
