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Contributor
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cpu wait and cpu ready

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Hi,

We have very high cpu wait times on our vm's (19000ms).

We also have very low cpu ready times (20ms)

I have not noticed any performance issues on either of the 2 networks

I was hoping someone could give, in laymans terms, a definition of both cpu wait and cpu ready.   The technical definitions i've seen online havent been very clear to me.

Also - what would be causing such a high cpu wait time on vms?  It seems to be the same wait time on all vm's on the server whether or not they have 1 vcpu or 2 or how much memory they have been allocated.

Info about our server:

HP Proliant ML350G6

Cpu Cores: 4CPus x 2.555 GHz

Processor Type:  Intel Xeon CPU x5550 @ 2.67Ghz

processor socets 1:

Logical Processors: 8

Hyperthreading:  active

no of vm's:  33 (mostly server 2003 server vms)

Appreciating any assistance,

Regards,

Simon

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VMware Employee
VMware Employee

CPU wait time is the amount of time a virtual machine did get scheduled but the processors have

nothing to process and so the CPU simply waits while the scheduled time for the virtual

machine clicks by.

CPU Ready is the time that the virtual machine was ready, but could not get scheduled to run on the physical CPU.

bascially cpu ready means the guest is waiting on the host, cpu wait means the host is waiting on the guest.

________________________________________ Blog: http://virtualiseme.net.au VCDX #201 Author of Mastering vRealize Operations Manager

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Immortal
Immortal
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Immortal
Immortal

but look of it with only 1 physical CPU and you have 33 VM, it would be over assignment of vCPUs.

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Enthusiast
Enthusiast

First let me say that sounds like an awful lot of VMs to me for that size system, if they are mostly Windows Server 2003 and are all running at once.  Also, be aware that if you run a VM with 2 vCPUs assigned to it, two physical cores must be available for it to run.  If you have a lot of 2 vCPU VMs, on a system without a lot of physical cores, it can result in a situation where you don't see a high CPU utilization, yet things appear to be waiting on CPU, because only a few of the VMs can ever be running at once.   Also, are you sure you aren't having a paging/swapping problem?   That many server 2003 VMs running at once are going to need a lot of memory.

mudtoe

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VMware Employee
VMware Employee

CPU wait time is the amount of time a virtual machine did get scheduled but the processors have

nothing to process and so the CPU simply waits while the scheduled time for the virtual

machine clicks by.

CPU Ready is the time that the virtual machine was ready, but could not get scheduled to run on the physical CPU.

bascially cpu ready means the guest is waiting on the host, cpu wait means the host is waiting on the guest.

________________________________________ Blog: http://virtualiseme.net.au VCDX #201 Author of Mastering vRealize Operations Manager

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