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Date: Thu, 13 Nov 2003 12:20:46 +1100
From: Christopher Vance <vance@aurema.com>
To: Daniel Ellard <ellard@eecs.harvard.edu>
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cc: freebsd-hackers@FreeBSD.org
cc: John Baldwin <jhb@FreeBSD.org>
Subject: Re: Confused about HyperThreading and Performance
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On Wed, Nov 12, 2003 at 06:07:58PM -0500, John Baldwin wrote:
>APIC is not on by default for 4.9, it will be for 5.2.  4.9 does have
>HTT on by default when you build an SMP kernel though.  Did you include
>'options HTT' in your 4.8 SMP kernel?  If not, you aren't actually
>using your second CPU.  Also, as someone else mentioned, setting
>'machdep.cpu_idle_hlt=1' can be useful on some HTT systems.  However,
>p4's have a problem with their interrupt routing that can leave the
>second CPU halted for a long time if you do that.

Just because you have a cpu with HTT doesn't mean you can use it.
Your motherboard and BIOS also need to be aware of it, and enable it.

-- 
Christopher Vance