Date: Fri, 19 Dec 2003 15:34:00 -0700 (MST) From: Scott Long <scottl@freebsd.org> To: Mike Tancsa <mike@sentex.net> Cc: stable@freebsd.org Subject: Re: to hyperthread or not to hyperthread Message-ID: <20031219152927.V47291@pooker.samsco.home> In-Reply-To: <6.0.1.1.0.20031219172103.092e4c90@209.112.4.2> References: <6.0.1.1.0.20031219172103.092e4c90@209.112.4.2>
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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. Scott
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