Hyperthreading in 6.x ... still frowned upon?

Robert Watson rwatson at FreeBSD.org
Thu May 4 09:17:40 UTC 2006

On Wed, 3 May 2006, Chuck Swiger wrote:

>> Is it still something that I should disable, and, if so, how in 6.x?
> You should test it for the workloads you have, but most of the time, HT 
> isn't especially helpful.  AMD64 CPUs come in dual-core format rather than 
> HT-enabled.  If you've seen "HT" or "HTT" applied to an AMD system, it's 
> likely an abbreviation for "HyperTransport" or "HyperTransport Technology".

The workloads I've seen the best improvement in performance for HTT have been 
ones involving a healthy blend of floating point and integer instruction 
mixes, or ones with a lot of memory stalls.  Something worth remembering is 
that HTT hardware has, in fact, improved since earlier CPUs, and I've seen HTT 
go from a net loss in some critical workloads to breakeven or win.  My 
recommendation would be to evaluate the performance impact of HTT against your 
specific workload and see what impact it has, but not be surprised if it 
doesn't help.

Robert N M Watson

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