On Fri, 4 May 2007 15:58:40 -0400, Bert Freudenberg <bert at freudenbergs.de>
wrote:

> I'm pretty sure this is not true, but more like what Damien wrote.  
> Basically all that HT does is having a second register set so you can  
> hold the state of two processes in the CPU at the same time.  
> Execution units are shared. Since one process seldomly utilizes all  
> execution units (due to "pipeline bubbles") the other process can use  
> the free units. This simply enhances throughput, but it's not like in  
> one process you only ever get half the speed.

Okay, well perhaps I misunderstood. I know a couple years ago we did a
bunch of research into this, because we were running 4-processor servers
with hyperthreading in each processor, and we were running 4 VisualAge
server images on each machine. By turning off Hyperthreading, we got a very
significant speed increase (not quite double, but close). With
hyperthreading on, we only ended up ever using 50% of the total CPU
available.

Later,
Jon

--------------------------------------------------------------
   Jon Hylands      Jon at huv.com      http://www.huv.com/jon

  Project: Micro Raptor (Small Biped Velociraptor Robot)
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