high CPU ready while low vcpu ratio

M. Belali
M. Belali used Ask the Experts™
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Hi,

We have an esx 6 server with 2 x 8 core cpu's and a total of 32 logical cores.

On this server we have 4 vm's. See below for the number of vcpu for each.

VM1: 1 vcpu (linux)
VM2: 1 vcpu (windows server 2012 R2)
VM3: 8 vcpu (windows server 2012 R2)
VM4: 10 vcpu (windows server 2012 R2)

How is it possible that sometimes we experience cpu ready times of 4% to 10%?

That shouldn't be the case for this amount of available logical cpu's and this amount of provisioned CPU's..

Any help is very welcome.

Thanks.
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Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
Do you have performance issues ? more information and logs required.

Author

Commented:
Hi,

Yes we have performance issues. What kind of information do you need?
VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
Commented:
So where do you think the bottlenecks exist, what type of analysis have you already completed, make model of server, firmware, buiold versions of ESXi, vCenter Server ?

Single server ?

VM Server functions

disk subsystem ?
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David FavorFractional CTO
Distinguished Expert 2018
Commented:
To slightly expand Andrews comments.

1) The only time a system is CPU bound is if the only tasks running are CPU based tasks. For example, crypto coin mining.

2) In all other cases, performance problems relate to IO, either network or disk.

Tip: Pull each of your VMs onto it's own physical machine + instrument the VM... Where instrument means test for I/O usage patterns.

Once you identify the I/O problem source, you'll likely either redesign the related code (might be as simple as adding indexes to an SQL table) or if data being hammered is small, you might place this data in a RAM disk or switch to using NVMe disks for one machine, where the I/O intensive code must run.

Summary: Unlikely CPU usage is the real problem. Likely it's I/O.

Author

Commented:
Hi,

Yesterday evening we did the following:
Turned off the VM's and restarted the host. In Bios we checked the power setting for the CPU, this was not set to performance, we changed this to performance setting. This morging (till now, 14:30 pm) the average cpu ready is back to "normal" 1% to 1,5%, a lot better then yesterday. Also no permorance issues today.

Could a CPU power setting have this big impact in this case? Didn't experience this before, even with servers with CPU power setting not set to performance.

We will monitor other I/O the coming days.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
Yes, you need to make sure your BIOS settings are as per recommended VMware settings in the guidance documents.

(and also changed in vSphere as well as the BIOS!)

Author

Commented:
Thanks!

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