Interpretation 'Average CPU Wait'

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Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Wed Oct 02, 2013 2:17 pm 2 people like this post

Dear

I'm not sure how I need to interpret the metric 'average CPU wait'

The help says: "CPU time the VM spent waiting for hardware or VMkernel lock thread locks."
So I would say that a high percentage would mean no good, since the VM is waiting for hardware.

My VMs have a high average CPU wait,
but I don't know why.
Image

CPU-, memory-, network- en datastore-usage looks OK.

Can any one help?

Best regards

Tom
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby Vitaliy S. » Wed Oct 02, 2013 2:57 pm 1 person likes this post

Hello Tom,

Be aware that high CPU Wait does not always result in bad VM performance. The total time of waiting CPU resources on the VMkernel level can be calculated using this formula %WAIT - % IDLE. So if %IDLE is equal to %WAIT, then everything is fine.

Thank you!
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Wed Oct 02, 2013 3:31 pm

Hey Vitaliy S.

Your formula is minus WAIT minus IDLE ?

Where can I find the value of %IDLE ?

Best regards

Tom
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby Vitaliy S. » Wed Oct 02, 2013 3:37 pm 1 person likes this post

I have corrected my post above, it is just WAIT minus IDLE. Idle performance metric is not used very often in troubleshooting, so please check it directly in vSphere Client.
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Wed Oct 02, 2013 3:49 pm

Ok Vitaliy
thx for you correction.

But when %IDLE is equal to %WAIT
the CPU WAIT percentage should be 0.

I've taken a look to the CPU-counters in the chart options in vSPhere Client,
but I didn't fid an IDLE-counter
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby Vitaliy S. » Wed Oct 02, 2013 3:52 pm

CPU IDLE can be found if you navigate to the VM in question -> Performance -> Advanced -> CPU realtime counters -> IDLE. Hope this helps!
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Wed Oct 02, 2013 3:57 pm

I only have this counters: wait, usage, swap wait, usage in mhz, used, ready, system.
no idle.
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby Vitaliy S. » Wed Oct 02, 2013 4:00 pm

Hmm...what vSphere version are you at?
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Wed Oct 02, 2013 4:02 pm

4.1.0
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby Vitaliy S. » Wed Oct 02, 2013 4:04 pm

Looks like this metric is only available via ESXTOP in vSphere 4.1.
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Wed Oct 02, 2013 4:08 pm

ok Vitaliy

I've never used that,
but I'll give it a try.

But what about this remark?
"But when %IDLE is equal to %WAIT
the CPU WAIT percentage should be 0."

I'm obviously still interpreting something differently then you.
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby Vitaliy S. » Wed Oct 02, 2013 4:13 pm

%WAIT includes %IDLE by default, in other words %WAIT- %IDLE = X, where "X" is the time spent waiting for the resources. Hope this makes sense.
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Fri Oct 25, 2013 8:13 am

Dear Vitaliy

Sorry, it took me some time to discover (r)esxtop.
(I had to work on another project)

This is what I see:

Image

There is no IDLE?
Is it possible that that metric doesn't exist in this version of Vsphere?

Best regards

Tom
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby Vitaliy S. » Fri Oct 25, 2013 11:33 am

Hmm... based on this link, it should be: http://pubs.vmware.com/vsphere-51/index ... nters.html

Can you please try following this blog post to get this value?
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Re: Interpretation 'Average CPU Wait'

Veeam Logoby tom.depoorter » Mon Oct 28, 2013 2:23 pm

Thanks for your post Vitaliy

It's strange: it seems to me that I'm not able to add those "Additional fields".
Could this be a difference between running esxtop for ESX and resxtop for ESXi?
(I keep searching)

If this value isn't available in ESXi
how veeam monitor gets this value?

Tom
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