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Date: Tue, 8 Jun 2004 16:45:12 -0500
From: Eugene Lee <list-freebsd@fsck.net>
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Subject: Re: Hyperthreading question
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On Tue, Jun 08, 2004 at 03:36:28PM -0400, Dwayne MacKinnon wrote:
: 
: I'm upgrading some machines from 4.8-RELEASE to 4.10-RELEASE. The 
: machines in question are dual-processor xeon boxes. Now, my boss is 
: adamant in that he doesn't want hyperthreading enabled on the machines.
: 
: In 4.8-RELEASE things were simple... I just didn't add the "options HTT" 
: line to my kernel config file. In 4.10-RELEASE though, HTT is enabled by
: default.
: 
: So, is there any way to shut off the hyperthreading? I've tried 
: disabling it in the BIOS, and had no luck whatsoever.

Hyperthreading is built into the kernel by default starting with
FreeBSD-4.9.  However, it is not enabled by default.  To do so,
do a "sysctl machdep.hlt_logical_cpus=0"