Re: to hyperthread or not to hyperthread

From: Harald Schmalzbauer (h_at_schmalzbauer.de)
Date: 12/20/03

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    To: Scott Long <scottl@freebsd.org>, Mike Tancsa <mike@sentex.net>
Date: Sat, 20 Dec 2003 12:40:12 +0100

    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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