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VMWare and cores

Posted on 2013-11-05
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Last Modified: 2013-11-05
I realize I am slow, but I need to ask this another way

Assuming I have a 4 core Intel with HT machine running, and I do the following

  - Click on VM->Edit Seetings-Hardware tab->CPUs

  - Number of virtual sockets:      1

  - Number of cores per socket:     2

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Does this mean I am using 2 of the 4 physical cores available in my system
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Question by:Los Angeles1
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Nick Rhode earned 200 total points
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Hyperthreading splits the cores so it works in this order.

Processor Socket = 1
Cores Per Socket = 4
Logical Processors (with hyperthreading) = 16

Without hyperthreading it would be 8 logical processors
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by:Frosty555
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It means that your virtual machine will be presented with two CPU cores, and will be able to take advantage of the benefits of having a multi-core system.

At the physical level, the hypervisor will decide how the virtual resources are served by the physical hardware. Very likely yes, two cores on your physical machine will work to serve the CPU needs of the virtual machine.

However, this doesn't mean you have "used up" the physical cores in the system. You can have many virtual machines sharing the physical CPU cores. Cycles on the physical cores that wasn't used by Virtual Machine A will be consumed by Virtual Machine B.

So long as the virtual machines do not cumulatively consume more CPU resources than the physical hypervisor can deliver, you're fine.
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by:insidetech
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I realize that this is somewhat confusing....
HT does not necessarily mean that the cores are X 2...

The HT intends to run two code pipelines in parallel, but not always. In non virtualized world the OS will report that is "sees double", but in reality you are not getting 2x performance all the time.

Now, the VMware will take all this in to an account and think of it as putting the sockets, cores and HT in a "blender". What comes out is computing resource of sort that you draw from with your VM's in a form of Virtual CPU's. For all practical purposes they represent how much computing resources you draw from the master CPU pool.
These Virtual CPU's no longer represent 1:1 relationship with the physical CPU's and so your VM OS will not recognize the processors as ones capable of HT.
By assigning more processors to your VM OS you are simply assigning more computational resources for that specific VM.
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by:insidetech
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Seriously?

1 X 4 with HT == 16 ????
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by:Nick Rhode
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ooops i mean 8.  Haha.  Sorry all the servers I worked on have at least 2 socket quads.  Just a slip of the brain.

The above math would be

Processor Socket = 1
Cores Per Socket = 4
Logical Processors (with hyperthreading) = 8
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