to hyperthread or not to hyperthread

Scott Long scottl at
Fri Dec 19 14:33:31 PST 2003

On Fri, 19 Dec 2003, Mike Tancsa wrote:
> We are replacing a box that is fairly busy with many different processes
> (sendmail / pop3).  The new MB and CPU is hyperthreading capable. Is it
> worth it to enable this ?  Does anyone have any real world experiences with
> it in RELENG_4 that say one way or the other to use or not use it ?
> dmesg shows,
> CPU: Intel(R) Pentium(R) 4 CPU 3.00GHz (2992.52-MHz 686-class CPU)
>    Origin = "GenuineIntel"  Id = 0xf29  Stepping = 9
>    Hyperthreading: 2 logical CPUs
> 	---Mike

HyperThreading usually requires special smarts in the OS process
scheduler so that the cores don't bottleneck each other with cache
thrashing and pipeline stalls/starvation.  Without this, Hyperthreading
is usually slightly slower than non-Hyperthreading.  4.x does not have
a scheduler that understand HTT, but 5.2-CURRENT does.


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