[Wien] wien and hyperthreading

[Jeff Spirko]

With hyperthreading, you don't actually get to do twice as many
calculations per second on a single processor.  It allows the
processor to quickly switch from one process or thread to another
when the first process is waiting for something (like memory, disk,
etc.)  If both processes are using the floating point unit (FPU)
intensively, as Wien2k does through the BLAS library, the net result
is that the two threads just take turns calculating.

What HT might do is allow Wien2k and "regular" stuff like Netscape
and X Windows to run side-by-side a little more efficiently, because
they use different resources.  See how much playing a movie slows down
Wien2k with and without HT on.  There you should see some improvement.

Regards,
-Jeff Spirko

On Mon, Mar 14, 2005 at 03:31:08PM +0100, Michael Gurnett wrote:
>    I  was running some tests to compare speeds with hyperthreading on and
>    off  using  the latest kernels for redhat 7.3. However, I was not able
>    to  see any difference in speed between the two cases. I was wondering
>    if anyone else has seen this and possibly explain why this is.
>    Michael

-- 
Jeff Spirko   spirko at lehigh.edu   spirko at yahoo.com   WD3V   |=>

The study of non-linear physics is like the study of non-elephant biology.

All theoretical chemistry is really physics;
and all theoretical chemists know it. -- Richard P. Feynman