machdep.hyperthreading_allowed does not affect SMT cores

lokadamus at lokadamus at
Fri Sep 7 19:16:37 UTC 2012

On 09/04/12 18:01, Ryan Stone wrote:
> I have a Intel Sandy Bridge system that reports that it has SMT cores
> instead of HTT(under a derivative of FreeBSD 8.2).  I'll admit that I
> don't at all understand the distinction between the two -- I thought
> that HTT was just Intel's name for SMT.  In any case, is there any
> reason that machdep.hyperthreading_allowed should not apply to SMT
> cores, too?
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No, HTT is a half core. It will speed up a system round about 20%, but 
only when it can work with HTT.
HTT is the idea to work on the last thing while new data will transfer 
from ram to cpu cache.
Else the cpu wlll idle and doing nothing.

Problem is to use htt on a heavy loaded system. Since Win7 Microsoft use 
it on a good way. Bevor this, they make a mistake to use it as a normale 
core. Under Vista cpu 0 is under heavy load they put it to cpu 1, but 
this was only a htt core.
On a dualcore core 2 must use, bevor core 1 (htt) is used. This it is, 
what MS change.

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