From owner-freebsd-stable  Fri Feb 28 11:25: 6 2003
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From: Don Bowman <don@sandvine.com>
To: 'Steve Grandi' <grandi@noao.edu>, freebsd-stable@freebsd.org
Subject: RE: hyperthreading in STABLE: should machdep.cpu_idle_hlt be on?
Date: Fri, 28 Feb 2003 14:24:50 -0500
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> From: Steve Grandi [mailto:grandi@noao.edu]
> I've brought up STABLE on a Supermicro X5DPR-8G2+ motherboard 
> which has
> two 2.4GHz Xeons.  In the BIOS setup, I disabled 
> hyperthreading.  The BIOS
> even prints out a nice message during the POST that hyperthreading is
> disabled.
> 
> The BIOS setting notwithstanding, STABLE fires up hyperthreading and
> presents me with 4 cpus!
> 
> OK, I will go with the flow: but what is the current wisdom about
> machdep.cpu_idle_hlt?  Should I set it to 1 to avoid a loss 
> of performance
> and to avoid frying the box?

On that motherboard, with our application, we've found that 
enabling hlt=1 will drop 0.1A of power on the inlet, or about ~12W
(going from 2.15A to 2.05A).
Our performance increased approx 7% for the same network-centric
application, YMMV.

We use hyperthreading enabled in the BIOS, and an SMP kernel,
it has proven to increase performance in our application.

--don

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