One of the key performance counters in a vSphere enviroment is: CPU ready (%rdy in ESXTOP)
CPU ready is the time a virtual CPU is ready to run but is not being scheduled on a physical CPU. This would under normal circumstances indicate that there is not enough physical CPU resources on an ESX/ESXi host. This is the first go-to counter when your users complain about bad performance.
The CPU ready counter is accessible from the vSphere Client and from ESXTOP. I have made two screenshots showing the a virtual machine and its ready time:
vCenter Performance Graphs (Value 1035 milliseconeds)
ESXTOP (value 5.38%)
What we see is a virtual machine with a ready time of 1035 ms. or 5.38%. These numbers are actually telling us the same thing. When we are using the performance graphs the graph updates every 20 second (or 20,000 millisecond). With a ready time of 1035 ms. we can change it to a percentage: (1035 ms. x 100) / 20000 ms = 5,175%
To be able to interprept ready times it is essential to know the relationship between the percentage of ESXTOP and ms. of the Performance Graphs. You are seeing the same numbers. One is in milliseconds the other is a percentage.
1% = 200 ms.
5% = 1,000 ms.
10% = 2,000 ms.
100% = 20,000 ms.
In general you want to see virtual machines with a ready time lower than 1000 ms. or 5%.
Read more about ESXTOP here
Just heard of a cool calculator to convert cpu ready times to a percentage: http://www.vmcalc.com/