Some documents, such as VMware's whitepaper Performance Troubleshooting for vSphere 4.1 refer to the CPU ready value as a summation value. Other documents, such as the vSphere Datacenter Administration Guide, refer to the CPU ready value as a percentage value. Therefore, you may need to convert between CPU ready summation and CPU ready percentage values to troubleshoot some performance issues.
To convert between the CPU ready summation value in vCenter's performance charts and the CPU ready % value that you see in esxtop
, you must use a formula.
The formula requires you to know the default update intervals for the performance charts. These are the default update intervals for each chart:
CPU ready %
To calculate the CPU ready % from the CPU ready summation value, use this formula:
(CPU summation value / (<chart default update interval in seconds> * 1000)) * 100 = CPU ready %
For example:
The Realtime stats for a virtual machine in vCenter might have an average CPU ready summation value of 1000. Use the appropriate values with the formula to get the CPU ready %.(1000 / (20s * 1000)) * 100 = 5% CPU ready
To convert the CPU ready % into a CPU ready summation value, reverse the calculation and use this formula:
(CPU ready % / 100) * <chart default update interval> * 1000 = CPU summation value
For example:
If a virtual machine has a CPU ready % of 5m, its CPU ready summation value on the Realtime performance chart is calculated like this:(5 / 100) * 20s * 1000 = 1000 CPU ready
As a shortcut, you can use the following formulas for the default chart update intervals to get the CPU ready %:
Example: A realtime CPU summation value of 1000 is divided by 200 to give a CPU ready % of 5.