Re: Detection of HyperThreading (fwd)

[Pieter De Wit]

Hi Guys,

Below is a post I made to cpufreq - obviously the wrong list (Sorry guys). 
Dave has helped me, but I would like to know if I understand his reply 
correctly.

In a nutshell, what he is saying is that the HT flag is "really" a flag 
that says the CPU can report (as per Intel's site) cores vs threads ?

I am wondering if this isn't confusing for the avg Joe in the street (it 
had me going for a while) claiming that the CPU has HT, when it rather has 
the capability to report a HT core (for lack of a better description)

In other words, shouldn't/should there be something else indicating a 
certain "core" is really a HT "thread" (in /proc/cpuinfo)

(Please correct me if I mis-understood the topic/reply)

Thanks,

Pieter

---------- Forwarded message ----------
Date: Mon, 2 May 2011 12:15:57 -0400
Cc: cpufreq@xxxxxxxxxxxxxxx
Subject: Re: Detection of HyperThreading

On Mon, May 02, 2011 at 03:47:30PM +1200, Pieter De Wit wrote:
 > Hello Guys,
 >
 > I found something quite weird over the weekend. I have a few machines that
 > claim they have HT (using cat /proc/cpuinfo). These machines doesn't
 > really support HT (both with the number of threads and Intel's website)
 >
 > I was wondering:
 >
 > a) Is this the right list to send to (Sorry if not)

no, this list is for cpu frequency scaling. linux-kernel would have been
more appropriate.

 > and
 >
 > b) How is the HT flag detected ?
 >
 > CPU's like the Core2 Duo E6300 doesn't have HT, but yet the flag is
 > displayed ? See http://ark.intel.com/Product.aspx?id=27248 for info. I can
 > send a dump of /proc/cpuinfo later from home.

the 'ht' flag in /proc/cpuinfo means "this cpu knows how to report how
many siblings it has".  On a CPU which doesn't have hyperthreading, that
number will be 0.

	Dave

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