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From: Robert Watson <rwatson@FreeBSD.org>
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To: Dag-Erling =?iso-8859-1?Q?Sm=F8rgrav?= <des@des.no>
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References: <461E0078.3050001@cisco.com> <evl00c$89j$1@sea.gmane.org>
	<461E092B.4080001@cisco.com> <86d529zxci.fsf@dwp.des.no>
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Cc: Randall Stewart <rrs@cisco.com>, freebsd-current@freebsd.org,
	Ivan Voras <ivoras@fer.hr>, Brad Penoff <penoff@cs.ubc.ca>,
	Janardhan Iyengar <iyengar@conncoll.edu>
Subject: Re: CPU utilization
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On Thu, 12 Apr 2007, Dag-Erling Sm=F8rgrav wrote:

> Randall Stewart <rrs@cisco.com> writes:
>> machdep.hyperthreading_allowed: 0
>
> Note that enabling hyperthreading is more likely to harm performance than=
 to=20
> help it.  You should just disable it in the BIOS, and run a UP kernel.

Historically this has been true, but some more recent results I've seen=20
suggest that both hyperthreading hardware has improved, and the efficiency =
of=20
our SMP implementation and scheduler has lead to it being more effective us=
ed.=20
I would reevaluate this on more modern hardware and using a more recent ker=
nel=20
before assuming this remains true for your application.

Robert N M Watson
Computer Laboratory
University of Cambridge
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