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From: Pete French <petefrench@ticketswitch.com>
Date: Fri, 27 Jan 2006 19:24:06 +0000
Cc: 
Subject: Re: How do I turn off hyperthreading on 6.0 ?
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> Disable it in the BIOS.  The kernel can't use what isn't advertised as 
> available.  :)

true - but surely this is a bug in FreeBSD ?

man smp says:

"Since using logical CPUs can cause performance penalties under certain
loads, the logical CPUs can be disabled by setting the
machdep.hlt_logical_cpus sysctl to one."

I have:

websvr04# sysctl machdep.hlt_logical_cpus
machdep.hlt_logical_cpus: 1

but I am still seeing 4 CPU's as I have two physical processors, each with
two logical ones onboard.

I find it very hard to believe theres a bug in something this basic though,
as it's specificly mentioned in the relase notes as being there to disable
hyperthreading...

very odd...

-pete.