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List:       freebsd-stable
Subject:    Re: to hyperthread or not to hyperthread
From:       Harald Schmalzbauer <h () schmalzbauer ! de>
Date:       2003-12-20 11:40:12
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On Friday 19 December 2003 23:34, Scott Long wrote:
> 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
> >   
> > Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,
> >MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,S SE2,SS,HTT,TM,PBE>
> >    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.

Do you mean ULE or 4BSD regarding HTT capable?

Thanks,

-Harry

>
> Scott
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