esxi cpu usage in mhz vs %

[chocobongo]

Hi,

I have question re the above.

I have an environment which esxi host showing high CPU usage in MHz but low CPU usage in %.

Please see below graph.

I would like to understand the actual usage of the host.

I think the true consumption should be figures reflected on MHz.

Please advise.

[MikeStoica]

The CPU (%) chart displays virtual machine CPU usage and ready values and CPU Usage (MHz) chart displays virtual machine CPU usage.

Check this link CPU (%)

[chocobongo]

The graph above is not from a vm. it's from a host.

Do you see issues or explanation of why CPU usage in % is low but MHz is high - they don't correlate each other.

Thanks

[MikeStoica]

Sorry. Read this CPU (%) for the host.

Actively used CPU(%), as a percentage of the total available CPU, for each physical CPU on the host. Active CPU is approximately equal to the ratio of the used CPU to the available CPU.

The sum, in megahertz, of the actively used CPU of all powered on virtual machines on a host

[chocobongo]

Sorry I don't get you.

You just copied the stuff out of the vmware doc.

What do you mean by "Active CPU is approximately equal to the ratio of the used CPU to the available CPU."

I have 4 physical socket installed on a host and under that host I have 5 vms each with 8vCPUs.

And I'm getting the result which is shown in the graph above.

Please explain this scenario as an example.

Also what I want to know is why the % and MHz don't correlate. there are big gap between the two as shown in the graph.

I need understanding on this please. 

Thanks

[daphnissov]

The reason those don't correlate is because they're two totally separate units of measurement--they aren't supposed to correlate. Moreover, MHz (or frequency) is a summation of the clock speeds of all physical cores on the host. If your ESXi host has 8 physical cores with the clock speed of each at 2 GHz, you have a theoretical maximum utilization of 8 x 2 GHz (16 GHz). Percent is, well per cent, of the entire scope.

[MikeStoica]

You already have there explained and calculation made. Same thing as daphnissov explained.

[Dave_the_Wave]

This question pops up a few times, you might be interested to see this thread which I have included some screenshots of the VM and the host:

CPU usage % and MHZ

[chocobongo]

In accordance to the graph above, Host CPU% usage is way below 20% even though Mhz shoots up 25000Mhz

So does this mean host physical CPUs have plenty of power and grunt to take on more VMs?

I just need to understand whether host CPUs are under stress therefore I require to add more hosts into the cluster or not.

[daphnissov]

In accordance to the graph above, Host CPU% usage is way below 20% even though Mhz shoots up 25000Mhz

We don't know that unless we know

1. How many physical cores this host has
2. The frequency of each core

Again, percentage and MHz are two totally different units of measurement. One is relative, the other is absolute.

I just need to understand whether host CPUs are under stress therefore I require to add more hosts into the cluster or not.

This is actually more complicated than you think and you aren't going to get a good answer just by looking at utilization graphs alone. This is why something like vRealize Operations is better because it gives you more information to make that judgement. There are other factors it considers than just utilization, which can often times be not very revealing.