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From: Mikael Pettersson <mikpe@csd.uu.se>
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Date: Fri, 10 Jan 2003 12:19:07 +0100
To: Dave Jones <davej@codemonkey.org.uk>
Cc: jamesclv@us.ibm.com, Jason Lunz <lunz@falooley.org>,
       linux-kernel@vger.kernel.org
Subject: Re: detecting hyperthreading in linux 2.4.19
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Dave Jones writes:
 > On Fri, Jan 10, 2003 at 08:05:07AM +0100, Mikael Pettersson wrote:
 > 
 >  > If the kernel has sched_setaffinity() or some other way of binding a process
 >  > to a given CPU (as numbered by the kernel, which may or may not be related
 >  > to any physical CPU numbers), then this will do it: execute CPUID on each
 >  > CPU and check the initial APIC ID field. If you find one that's non-zero,
 >  > then HT is enabled.
 > 
 > That's a horrible way of reimplementing /dev/cpu/x/cpuid  8-)

True. I forgot about that interface since I personally never configure or use it.

So this answers the original question. Just access /dev/cpu/$CPU/cpuid
for all (accessible) values of $CPU.
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