CPU Ready value is cumulative between the number of vCPUs the VM is assigned. For example, a one vCPU VM has the measurement of 1000ms. For a VM with two vCPUs, the same performance drop would rise to 2000ms, or 1000ms per vCPU. For a VM with four vCPUs, it would be 4000ms.
CPU Ready / (interval * 1000) * 100 = Performance Penalty
Statistics Rollup Intervals
vCenter defines the following default intervals for rollups:
- Real-Time: 20s interval (20 seconds)
- CPU Ready / (20 * 1000) * 100
- Daily: 5m interval (300 seconds)
- CPU Ready / (300 * 1000) * 100
- Past Week: 30m interval (1800 seconds)
- CPU Ready / (1800 * 1000) * 100
- Past Month: 2h interval
- CPU Ready / (7200 * 1000) * 100
- Past Year: 1d interval
- CPU Ready / (86400 * 1000) * 100
Real World Examples
Here is a Database server real-time graph. The average CPU Ready is 609.
609 / 22000 * 100 = 2.76% CPU Ready
On this particular DB server, it was configured with 8vCPU.
After reducing the vCPU from 8 to 4, I used the next available day to review performance improvement (or not).
I can see now that my average is 7420ms, or 2.76% performance degredation. Performance improvement of almost 45%!