[nSLUG] Hyperthreading

Eric R. Smith ersmith at hfx.eastlink.ca
Fri Jan 9 15:43:36 AST 2004


Peter Cordes wrote:
> On Wed, Jan 07, 2004 at 11:16:25AM -0400, George N. White III wrote:
> 
>>Say you get HT working -- how much benefit will you see?
> 
>  For desktop stuff, think how great it would be for your X server and your X
> client to be running simultaneously?  You get the advantages of an SMP
> system, except for heavy duty calculations.  Your system will probably
> feel faster/more responsive.

There is the caveat that you still have only one physical processor. The 
simultaneously running threads have to contend for resources. 
Fortunately, many resources (e.g. registers, function units) are present 
in "overabundant" quantities, more than a single thread is likely to 
need, which is why HT is useful. But some resources (e.g. cache) are 
more limited.

I would imagine that a 2MHz HT processor would be faster than 2x1MHz 
processors on a few tasks (those where only one thread at a time needs a 
burst of CPU), but significantly slower on other tasks (e.g. those where 
the cache becomes significant). Anyone have any actual experience with this?

Eric




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