Question on hyperthreading .... with dual core CPU's

[Steven E. Protter]

We have an Intel Xeon based server with two dual core 3.2 GHz Intel CPU's.

In my mind that adds up to 4 CPU's.

The user that ordered the server thinks he'll get 8 hyperthreading CPU's. Perhaps the correct term is virtual CPU's.

The host OS is Red Hat Linux ES 4

I've been reading up on hyperthreading and don't understand why the user thinks he's getting 8 CPU.

To earn full points(10) please explain or provide links that give me the basis of hyperthreading and how CPU's are counted.

Regards,

SEP
NDS Israel

[Igor Karasik · Accepted solution]

Steven,I think user right.
Server will see 8 "logical" CPU.
See this advisory:
"Linux Installation May Halt or May Not Boot on Certain ProLiant Servers with Three or Four Intel Dual Core Processors"
http://www1.itrc.hp.com/service/cki/docDisplay.do?docLocale=en_US&docId=200000081720047
"Note: For the purpose of this document, a Dual Core processor is considered to be two logical processors and a Hyperthreaded processor is considered to be two logical processors. As a result, a Dual Core, Hyperthreaded processor is considered to be four processors."
See this advisory as well
"Insight Diagnostics Displays More Than One Processor Per Processor Chip On The System Board When CPU Hyperthreading Is Enabled"
http://www2.itrc.hp.com/service/cki/docDisplay.do?docLocale=en_US&docId=200000080893187

Intel have Processor Identification Utility
http://support.intel.com/support/processors/tools/piu/
which may help you too

[Oleg Koroz]

http://h18004.www1.hp.com/products/servers/technology/hyper-threading.html
http://www.intel.com/technology/hyperthread/index.htm

http://www.intel.com/technology/computing/dual-core/
see Demo: Dual-core and Hyper-Threading comparison


http://www.intel.com/business/bss/products/server/dual-core.htm?iid=search&

ftp://download.intel.com/products/processor/xeon/srvrplatformbrief.pdf
Each core supports HT Technology,
which allows it to present itself as two logical processors. Dual-core
processors with HT Technology can process four software threads
simultaneously by more efficiently using resources that otherwise
may sit idle-a total of 16 threads in a 4-way MP platform.

[Oleg Koroz]

just small typo


http://www.intel.com/business/bss/products/server/dual-core.htm?iid=search&

see Demo: Dual-core and Hyper-Threading comparison on the right side

[Steven E. Protter]

More points available:

Please tell me a simple way under Linux to demonostrate the existance of the 8 virtual CPU's.

Utility, X windows or not is just fine.

SEP

[Rob Leadbeater]

Hi Steven,

You can see how many CPUs Linux thinks its got in a couple of ways. The command line utility top is probably the quickest. The output below is from a Dual Xeon with Hyperthreading enabled (single core):

[root@server1 root]# top

CPU states: cpu user nice system irq softirq iowait idle
total 4.9% 0.0% 3.2% 0.0% 0.0% 0.0% 91.7%
cpu00 7.4% 0.0% 0.0% 0.0% 0.0% 0.0% 92.5%
cpu01 8.1% 0.0% 7.3% 0.0% 0.0% 0.0% 84.4%
cpu02 2.4% 0.0% 0.0% 0.0% 0.0% 0.0% 97.5%
cpu03 1.6% 0.0% 5.7% 0.0% 0.0% 0.0% 92.5%


You could also look at the startup messages in /var/log/dmesg for details about the CPUs.

Cheers,
Rob

[Steven E. Protter]

We have our answer.

Apologies to HP for the slight mis-use of this forum.

We ordered an IBM x336 server with two 3.6 Gigahertz CPU's. This shows up as 4 virtual CPU's just as everyone here said it should.

My internal customer wanted dual core technology, and I should have ordered it with one or two dual core cpu's which run at 2.8 Gigahertz.

Ooops on me.

Thanks for all your help.

SEP