Hyperthreading Kernel Configuration - 5.1

[Damian Gerow]

Thus spake John R. Shannon (john at johnrshannon.com) [02/10/03 13:05]:
> On a new computer, dmesg shows:
> 
> CPU: Intel(R) Pentium(R) 4 CPU 2.80GHz (2793.01-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,SSE2,SS,HTT,TM,PBE>
>   Hyperthreading: 2 logical CPUs
> acpi_cpu0: <CPU> port 0x530-0x537 on acpi0
> acpi_cpu1: <CPU> port 0x530-0x537 on acpi0
> 
> Should options  SMP  and  APIC_IO  be enabled in kernel?

In short: yes.  And then you need to look at the machdep.* sysctl nobs,
there's one you need to enable in there (I've forgotten which one).

But that leads me to a secondary question: is enabling HTT really worth the
time?  I know that people have said that using HTT can actually make your
system slower -- is this an implementation issue, or did Intel really
release something that degrades performance?