Question about VCpu and cores \ sockets

[millardus]

Hi folks

I am gathering some licensing data for our TSM Backup solution.

The auditors have asked for core and socket info for our VM's as well as the ESX Host they are on.

I can see that my ESX Hosts have 2 sockets and 4 cores in each (8 Logical processors) , but how does that translate to a VM on the host that has 4 VCPU's?

Does that VM have *4* cores??

Anyone know how to report on this?

M

[rickardnobel · Accepted solution]

Millardus wrote:

I can see that my ESX Hosts have 2 sockets and 4 cores in each (8 Logical processors) , but how does that translate to a VM on the host that has 4 VCPU's?

Does that VM have *4* cores??

In vSphere 4 a 4 vCPU configuration will typically look to the VM as 4 single-core sockets actually, but this could on 4.1 be changed (through editing the vmx file) to 1 socket with 4 cores if you wish.

[weinstein5]

In short a vCPU will equate to single LCPU 

[vGuy]

Also have a look at this kb:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=101018...

[helltejas]

Hi

Setting up Socket in VM is a new feature in vSphere 5. now we can make vCPU with Multicore.

1 socket 4core vCPU has less overhead then 4 vCPUs. and vSMP becomes very efficient

I hope this is the answer you are looking for

[rickardnobel]

Tejas wrote:

Setting up Socket in VM is a new feature in vSphere 5. now we can make vCPU with Multicore.

Actually it was possible already in vSphere 4.1, but not through the GUI.

1 socket 4core vCPU has less overhead then 4 vCPUs. and vSMP becomes very efficient.

Could you give any reference to that? There are no known information as far as I know that it should anything performance related in this, but just a matter how you want the vCPUs to look to the VM concerning licensing.

[beckham007fifa]

another thing,

1 socket 4core vCPU has less overhead then 4 vCPUs.

what is the difference in this unless I assume you are going to change dafaults for cpuid.corespersocket value to something which is relevant.

[TomHowarth]

1 socket 4core vCPU has less overhead then 4 vCPUs. and vSMP becomes very efficient

I assume that you are talking about the guest OS and not the Host,  as from ESXi's point of view there is no difference in scheduling.

[beckham007fifa]

yes indeed Tom,  there is no difference in

1 socket 4core vCPU has less overhead then 4 vCPUs. and vSMP becomes very efficient.

So, how SMP becomes very efficient with this.

[helltejas]

Hi guyz,

i think On a dual-core CPU (or dual-CPU system) the game can never use more than 100% of 1 CPU. But the OS (windows/Linux/etc.) schedules some steps on core 1, the next 'x' steps on core 2, then the next group run on core 1 again. Why? must be trying to even the load. But it runs the same as it would if there were only 1 core. Where a game will run 'faster' on a dual core system is because while the game is running, Windows (or Linux/whoever) has system services to keep up - things like anti-virus scanning, spyware scanning, responding to requests from the internet, maybe another VM  downloading an MP3 from this VM, whatever.., and those services would interrupt the game if there was only 1 core. Since there's 2 cores, the game keeps getting 100% of a core because the other core can take care of those 'misc. and sundry' tasks.

In physical environment multiple sockets works 99.99% same as multicores but data transfer rate is lower because of BUS latency between 2 sockets.

That’s why i posted 1 socket 4core vCPU less overhead then 4 vCPUs.

Please currect me if i am wrong

Thanks

[helltejas]

Hi,

Reason to introduce Socket concept because of OS limitations

ex.

MultiCore:

Windows 7 was designed to work with today's multi-core processors. All 32-bit versions of Windows 7 can support up to 32 processor cores, while 64‑bit versions can support up to 256 processor  cores.

Multiple Processors:

Windows 7 Professional, Enterprise, and Ultimate allow for two physical processors, providing the best performance on these  computers. Windows 7Starter, Home Basic, and Home Premium will recognize only one physical processor.

http://windows.microsoft.com/en-US/windows7/products/system-requirements

[TomHowarth]

Although you are correct here, the Original Posters question relates to the interaction between a guest with 4 sockets, and a guest with 4 vCPUs and the underlying ESXi.

and in this particular situation there is no difference in Scheduling.

[helltejas]

Hi,

Can you provide me command reference to create socket with multiple cores in vSphere 4.0?

Thanx

Regards,

Tejas

[helltejas]

Yes i am completely agree with you tom.

There will be no difference in scheduling because those VMs are just a process to vmkernal

[rickardnobel]

Tejas wrote:

Can you provide me command reference to create socket with multiple cores in vSphere 4.0?

In 4.0 it is experimental, but supported in 4.1.

See KB article: http://kb.vmware.com/kb/1010184