The Cloud->Nodes section of the admin UI is always reporting 0% CPU even on very busy Solr nodes. I thought the attached patch would fix t, but it doesn't seem to be working. Instead of always 0%, it now shows an occasional 50% or 100%... and even rarer is a different percentage like 84% or 17%. The Solr process at that time was usng about 180% CPU (two CPUs in AWS instance).
Using OperatingSystemMXBean from com.sun instead of java.lang seemed to work fine in a quick test program, but it's not working in Solr. I am trying this on Ubuntu Linux with OpenJDK 17 and 11.