Converting between CPU summation and CPU % ready values

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

This KB helps in converting CPU Ready Summation and CPU Ready Percentage values to troubleshoot some performance issues.

For more details, refer CPU Ready 

Resolution

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:

• Realtime: 20 seconds
• Past Day: 5 minutes (300 seconds)
• Past Week: 30 minutes (1800 seconds)
• Past Month: 2 hours (7200 seconds)
• Past Year: 1 day (86400 seconds)

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

CPU ready summation value

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

Note: The result of above calculations are a sum of each virtual CPUs %RDY time. Individual core Ready time can be roughly estimated by dividing by the number of cores. However, it is more accurate to go by the vCPU metrics themselves. vCPU metrics are only collected in real-time by default.

Additional Information

CPU ready %

As a shortcut, you can use the following formulas for the default chart update intervals to get the CPU ready %:

• Realtime: CPU summation value / 200
• Past Day: CPU summation value / 3000
• Past Week: CPU summation value / 18000
• Past Month: CPU summation value / 72000
• Past Year: CPU summation value / 864000

Example: A real-time CPU summation value of 1000 is divided by 200 to give a CPU ready % of 5.

CPU ready summation value

As with the longer version of the formula, reverse the formula and multiply (rather than dividing) to calculate the CPU ready summation value:

• Realtime: CPU ready % * 200
• Past Day: CPU ready % * 3000
• Past Week: CPU ready % * 18000
• Past Month: CPU ready % * 72000
• Past Year: CPU ready % * 864000

Example: If you have a CPU ready % 5, multiply it by 200 to get a Realtime CPU ready summation value of 1000.