From owner-freebsd-questions@FreeBSD.ORG  Mon Aug 29 17:27:41 2011
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To: freebsd-questions@freebsd.org
References: <201108291724.LAA18734@lariat.net>
Date: Mon, 29 Aug 2011 12:27:32 -0500
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From: Mark Felder <feld@feld.me>
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Subject: Re: Turn off hyperthreading on dual core Atom?
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On Mon, 29 Aug 2011 12:24:08 -0500, Brett Glass <brett@lariat.net> wrote:

> With hyperthreading, the FreeBSD scheduler simply acts as if there are 4  
> CPUs. Each "CPU" gets clock interrupts (which add overhead), and the  
> scheduler is naive about the fact that two of the "CPUs" are not  
> separate chips and could be held up if its mate has a heavy load. I do  
> not know if the supposed higher utilization of the resources on each  
> chip (including executing one thread while the CPU waits for data for  
> another) is worth it. What has your experience been?

In my experience hyperthreading is useful in very few environments. I
personally disabled it on my Atom machine which acts as a NAS among
other things. I have noticed an improvement in performance and also in
responsiveness. YMMV, etc etc etc :-)


Regards,


Mark