Virtual CPU and Logical processors

[euphony]

I am trying to find the difference between a Virtual CPU and a Logical processor.

How many logical processors you have is dependant on how may cores you have on a processor, is that a correct.

Also how does enabling hyperthreading give you more logical processors.

Giving VM 2 VCPU means that it will use 2 logical processors, is that correct.

Any feedback would be appreciated, as I need to get an understanding.

[dkfbp]

A server with two quad core processors would have the following:

Processor sockets 2

Processor Cores pr. socket 4

Logical processors 8

You are right that when you give a vm two vCPU it will use two logical proseccors.

[euphony]

If Hyperthreading was available and was enabled would we get more logical processors.

Or is Hyperthreading only available when you have 2 dual processor with no cores.

Does hyperthreading improve performance. If it creates more logical processors are the same as the cores logical processors.

[dkfbp]

Hyperthreading has been removed from the newer Intel Processor lines. So if

you are running on new hardware don't worry about it.

An ESX server will see a hyperthreaded core as two logical processors. Hyperthreading can improve

performance.

[TomHowarth]

HyperThreading can improve performance, true but not as much as a core can. You are correct that HT has been disabled on the latest Intel Processors.

Tom Howarth

VMware Communities User Moderator

[RParker]

If Hyperthreading was available and was enabled would we get more logical processors.

Not true. Hyperthreading was the predecessor to the new CORE technology. There are no CORE processors with hyperthreading. It was a way to get a few more cycles out of a processor, but a logical processor from a hyperthreaded CPU is less than 20%. So you are getting 1 clock cycle and 20% of another clock cycle, which is why hyperthreading in ESX doesn't give good performance, depending on application.

CORE replaced hyperthreading, which no longer exists, at least for the new breed of processor.

[alfulfo]

My question has less to do with HyperThreading but is in the same realm.

I have the following:

Dell R410

2 X Intel Xeon L5520  (4 cores and 8 threads)

16GB memory

Product: ESXi 4 Single Server Licensed for 2 physical CPUs (1-6 cores per CPU)
License Key: xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
Expires: Never

When I look in at the summary of my server is shows the following.

CPU Cores:                    4 CPUs X 2.26GHz

Processor Type:              Intel(R) Xeon(R) CPU

                                      L5520 @ 2.27GHz

Processor Sockets:          2 <-- Correct

Core per Socket:              2 <-- Incorrect

Logical Processors:          8 <-- Correct if HyperThreading doesn't count

HyperThreading:                Active

How does the math work on this if HyperThreading doesn't count.

2 sockets x 2 Cores per socket != 8 Logical Processors

Help!