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From: Mark Watts <m.watts@mrw.demon.co.uk>
To: linux-kernel@vger.kernel.org
Subject: Re: Xeon  processors &&Hyper-Threading
Date: Sat, 14 Jun 2003 14:50:11 +0100
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> You recompile the kernel for SMP as well as P4. If the motherboard
> hasn't disabled HT capabilities, you will take full advantage of
> the processor under Linux. Whatever "full advantage" means, is
> not absolute, but whatever it is, will be used to its fullest.
> Basically, if the code is I/O bound, you'll not see any difference.
> If the code is compute-intensive, you will.

I discovered that you need the 'CPU Enumeration' part of ACPI to be enabled 
otherwise the kernel only sees physical processors, not sibling HT processors 
- shouldnt this be selected automatically when you select SMP ?