Hyperthreading in P4

Ole W. Saastad ole at scali.no
Sun Apr 28 06:53:27 PDT 2002

New Pentium 4 processors has hyper threading capabilities
and when setting this the linux sees 4 cpus on each dual node.

I have done some testing with OpenMP programs and found that
for OpenMP threaded programs there is no performance gain in using 
the hypertheading. Using a number of threads that equal the number 
of real processors seems to be optimal.
However, this is the results from just a few OpenMP programs and
might not tell a full story. 
I would like comments from others who has played with threads 
and hyperthreading in a Pentium 4 processor environment.

Hyperthreading is claimed to perform better when running a large
number of processes and a high number of threads. But this is most
probably different applications or different requests lets say to a 
web or db. server.

Ole W. Saastad, Dr.Scient. Scali AS P.O.Box 150 Oppsal 0619 Oslo NORWAY 
Tel:+47 22 62 89 68(dir) mailto:ole at scali.no http://www.scali.com 
Are you meeting Petaflop requirements with Gigaflops performance ?
    - Scali Terarack bringing Teraflops to the masses.

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