Cores per vCPU

Question

We're running ESXi 4.1 on R710 servers with dual E5645 processors, 2 sockets, 12 cores. We have a new VM running W2K8 R2 Std. I initially assigned 4 vCPU. The software publishers would like 8 cores. I followed the instructions in VMware KB Article: 1010184. I added

cpuid.coresPerSocket = 2

to the configuration file.

The core info shows 4 cores and 2 sockets

Logical to Physical Processor Map:
*--- Physical Processor 0
-*-- Physical Processor 1
--*- Physical Processor 2
---* Physical Processor 3

Logical Processor to Socket Map:
**-- Socket 0
--** Socket 1

I think this is a step in the right direction, but VMware won't start the VM if I try to add more than 4 cores. Is this because the vSphere 4 Ent license won't allow more than 4 vCPUs per guest even though the configuration allows me to select up to 8? Or am I doing something wrong?

The bottom line is that we want to give this application (Oracle 11g database for an accounting package) plenty of resources.

Thank you,

Ira

sketchy00 · Answer

To emulate a dual socket quad core arrangement, the cpuid.coresPerSocket setting should equal 4.  BUT... Be careful.  Is there actual evidence to support those kinds of requirements?  There might be, but prove it first.  This might help.  itforme.wordpress.com/.../resource-allocation-for-virtual-machines

Kong Yang · Answer

Hi @isibulkin,

I think that there are two things worth noting here if I read your post correctly:

First, you are correct in stating that vSphere 4 Enterprise will only allow you to create 4 vCPU VMs because of the 4-way vSMP limit on Enterprise per the VMware vSphere 4 licensing doc. If you have Enterprise Plus, your limit would be 8-way vSMP VMs. In sum, you would need Ent Plus license to support an 8-vCPU VM.

Second, if you have Enterprise Plus and you want 8 cores for your R710 config, then you should set vCPUs to 8 and you should change cpuid.coresPerSocket from 2 to 4. With the previous setting of 2, you will only see 4 cores because 2 cores by 2 sockets = 4 total cores. If you change the cpuid.coresPerSocket value to 4, you should see 8 cores because 4 cores by 2 sockets = 8 total cores. So when you assign 8 vCPUs to the VM, the 8 cores will result in 2 virtual quad core CPUs to the guest OS.

Regards,

Kong

sketchy00 · Answer

Accurate, but not very thorough (I kind of forgot about the Enterprise Plus thing...).  Your response gets the prize for that.

Kong Yang · Answer

Thanks for the reply sketchy00. That was spot on.

Virtualization General

Cores per vCPU

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