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Date: Mon, 29 Aug 2011 15:15:02 -0600
To: Bruce Cran <bruce@cran.org.uk>
From: Brett Glass <brett@lariat.net>
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Cc: questions@freebsd.org
Subject: Re: Turn off hyperthreading on dual core Atom?
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At 01:55 PM 8/29/2011, Bruce Cran wrote:

>Actually, the ULE scheduler does know about HyperThreading and the 
>topology of such CPUs. I don't know what it does with the 
>information, but it probably works to optimize cache usage etc.

Alas, during a recent kernel build, I used the -j2 command line 
option in "make" and watched as the scheduler repeatedly assigned 
two instances of cc (the most CPU-intensive program) to the same core.

During that process, I also watched CPU utilization in top(1). The 
peak was 46% idle, which means that HTT appeared to be making at 
most a 4% difference. (If the peak were 50% idle, HTT would be 
doing nothing at all, because top(1) can't tell that there aren't 
really 4 CPUs.)

--Brett Glass