Why CPU Usage showing spiky line when Demand showing a smooth line?

[Iwan_Rahabok]

I always thought that CPU Demand should be identical with CPU Usage, because both are average. So the chart below comes as a surprise to me. This is from vCenter 5.5 Update 1. There is no contention, as can be seen from the Entitlement counter.

The values are actually the same. The Demand line is somehow an average of the Usage. When both values are rolled up to 5 minutes, they become identical. The data at vCenter Operations shows that.

Question: why is the line pattern so different? The Usage showing a spiky line while Demand shows a smooth line. The Demand line makes sense as it is an average of 20 seconds. The Usage is a bit strange as it fluctuates drastically.

Thank you

e1

[Iwan_Rahabok]

I had a discussion with a friend on this. The 2 counters are both average, and are tracking the same thing. One of them has to be the "wrong" one. We think the CPU Usage pattern is the misleading one, because each sample is 20 seconds. That is 20,000,000,000 nano seconds. There are also 2 low point for 1 high point. It is strange for a CPU to be low for 40 billions nano seconds, then spike for 20 billion nano seconds.

The chart is from vCenter 5.5 Update 1. The host is ESXi 5.5

What do you think?