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mordzy
Enthusiast
Enthusiast

Guest CPU usage 100% Host CPU 45%

Hi,

My windows 2008 server has 4 cores assigned (Terminal server / P2V) and hits 100% cpu usage every day and grinds to a halt. having checked the host ESX that it is running on the CPU is only at 45%

I have no resource limits and the maximum usage is set to unlimited. i dont understand how this can be. please could someone explain for me?

This is the only server on the host at the moment.

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weinstein5
Immortal
Immortal

remember each vcpu will run on only one core at a time - so depending on what is running you might consider adding a extra vcpu and see if the resolves the issue

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mordzy
Enthusiast
Enthusiast

Thanks,

I have been advised in the past (all be it maybe wrong advice) that i dont really need more than 2 vcpu's anyway. As Vmware will allocate the entire power of all the physical cpu/cores to the two vcpu's if required. is this not the case?

also to clarify, the server is using 1 socket and 4 cores. the physical has 2x 4 core xeons

Thanks

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weinstein5
Immortal
Immortal

That is not the case - as an example using two vcpus on vm on an ESXi host with dual 8 corres and the 2 vcpus are 100% utilized only two of the 16 physical cores will be used -it is best practice to minimize the number of vCPUs because the more vCPUs you can run into an issue that can affect machine performance - like trying to run your VM on a physical machine with only 4 cores or 8 cores where other VMs are also running - which leads to my next question - whatis the configuration of the host this VM is running on -

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mordzy
Enthusiast
Enthusiast

Thanks for the insight.

The server is using 1 socket and 4 cores. the physical has 2x 4 core xeons.


am i right in thinking the maximum core count i can have on one socket is 4vcpu? also it does warn me of adding more may make windows unstable.



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BenLiebowitz
Expert
Expert

Keep in mind that by having 1 socket and 4 cores, the VM may be waiting for CPU time for one of the two sockets to have 4 cores available.  You can see if this is happening by looking at the performance tab...  click advanced, click chart options, Under CPU, change the time counter to 1 day, under Counters, deselect Usage in MHz and select READY.  The higher the ready value, the more time spent waiting. 

Ben Liebowitz, VCP vExpert 2015, 2016, & 2017 If you found my post helpful, please mark it as helpful or answered to award points.
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MauroBonder
VMware Employee
VMware Employee

Just curious Validate that the devices processor drives are ok within the W2K8. See but has nothing like "unknown device"

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jdptechnc
Expert
Expert

The guest OS is reporting 100% utilization.  Specifically, "WHAT" is using the CPU resources, from the perspective of the guest OS?  If Task Manager is showing several application processes as the highest consumers of CPU, then you may just need more vCPU.  If "System" is using a large amount to CPU, you may have another issue that is rooted in the kernel or device drivers (an actual driver problem, high I/O, antivirus problems, large amounts of open file handles, or anything that might be interacting with the kernel).

Please consider marking as "helpful", if you find this post useful. Thanks!... IT Guy since 12/2000... Virtual since 10/2006... VCAP-DCA #2222
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fayelund
Contributor
Contributor

We are having the same problem. For some reasons the guests looks to be unable to utilize the CPU properly. This also happens in environments where there are more than enough physical cores.

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JonathanKohler
Enthusiast
Enthusiast

Mordzy,

I am guessing that warning is coming up at the edit setting menu in vSphere, when you try to add more?

If so , It is warning you because some OS's take issue with CPU's being added or subtracted.

Keep in mind the following, Weinstein pointed out, You can absolutely add more vCPU's, just keep in mind that the rule of thumb is to never have more vCPU's on a VM, than physical cores in the box. You also want to be careful of having too many vCPU's (spread amongst many VM's) on the same physical host, as that can cause degradation.

That said, if this is the only VM on the box, you could try snapshotting the server first, then adding another vCPU, and seeing how that affects the performance of your VM.

Jonathan

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JJsilversmith
Contributor
Contributor

Having the same issue here.  Loading it up with Prime95 one our HP/vSphere5.5 gives us 100% CPU usage.  Doing the same on our new Cisco UCS/VMWare 6.0 maxes right at 45%.  Clone of the same VM.  What am I missing here?

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