I am troubleshooting some VMs that appear to be having problems. They are 4vCPU terminal servers and when I watch esxtop the CPU-ready reaches 40%+ quite often, but for fairly short periods of time. As these servers are time critical I presume that the user complaints of slow office apps and freezing may be down to this. I've only monitored it visually with esxtop, the vCenter rollups are not granular enough to show the problem.
I have inherited a vSphere farm that has a lot of memory, but is very much overcommitted for CPU with many high vCPU guests.
My question is what effect does high CPU ready have on the performance logs of the host and guest?
What effect on host CPU utilisation as viewed by vCenter?
What effect on guest CPU utilisation as viewed by vCenter?
What effect on guest CPU utilisation as shown by the perf logs in Windows?
If the CPU is unable to do work because the VM cannot be scheduled on it, does it show low utilisation even though in effect some cores are locked and unavailable for work? Or to put it another way Windows is asking the CPUs to do work, but the CPUs are not able to respond which is similar to if they were running at 100%. But how does Windows see this.
I'm trying to clarify how CPU ready effects stats as I will be asked by management to explain this and they are used to CPU utilisation graphs, but this will take a bit more explanation. They would have no problem with change requests to try to reduce load if they saw high CPU utilisation. Explaining CPU ready and providing stats is a bit more vague.
Thanks
Stuart