[clug-talk] Hyper-Threading core count?

[Aaron J. Seigo]

On Tuesday 04 October 2005 09:24, Roy Souther wrote:
> Anyone running Intel Xeon's with Hyper-Threading? Does each CPU show up
> as a dual core?

people seem a bit confused in this thread, probably thanks to the marketing 
wonks in the processor industry =)

dual core and hyper threading are completely different animals. both will 
result in `cat /proc/cpuinfo` showing two entries for each "processor" but 
the performance results are very different.

in hyperthreading, you essentially are able to run another thread or process 
on the same core utilizing unused pipelines on the chip. since modern 
processors have several parallel execution pipelines and applications can 
rarely fill them all at the same time, the idea is to try and utilize the 
unused pipelines whenever possible. this means you squeeze a bit more 
performance out of the single core in certain scenarios. IIRC you can expect 
~10% improvement in best case scenarios.

dual core, on the other hand, is true multi-processing: you have two distinct 
cores with their own sets of pipelines, registers, etc. essentially you have 
dual processors on a single die. this allows one to squeeze more processors 
into less space and also should in theory allow for better process migration 
and memory affinity due to cores being on the same die and therefore 
physically closer.

-- 
Aaron J. Seigo
GPG Fingerprint: 8B8B 2209 0C6F 7C47 B1EA  EE75 D6B7 2EB1 A7F1 DB43

Full time KDE developer sponsored by Trolltech (http://www.trolltech.com)
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