RE: Hyperthreading and physical/logical CPU identification

[Jauder Ho]

Well, you could always take CPUs out... :)

--Jauder

On Mon, 29 Apr 2002, Grover, Andrew wrote:

> > From: Andrew Theurer [mailto:[e-mail]]
> > I would like to know if there is any way to confirm that I have
> > hyperthreading enabled, and my P4 CPUs are hyperthreaded.
> > Actually, from
> > something like /proc/cpuinfo, I'd like to figure out if I am
> > seeing 2/4
> > physical/logical processors, as a result from hyperthreading, or 4/4
> > physical/logical processors with no hyperthreading.  I know,
> > "If it's double
> > the number of physical processors, well you have
> > hyperthreading enabled."
> > The problem is, I have 4 physical processors, but kernel.org
> > kernels so far
> > do not recognize all of them.  2.4.18 will find 3, while
> > 2.5.11 will find
> > only 2 (BIOS hyperthreading support off, no acpismp=force).
> > However, on
> > 2.5.11, if I enable hyperthreading (thru BIOS and
> > acpismp=force, I see 4
> > processors.
> >
> > I would very much like to believe that in this configuration,
> > I am only
> > running on 2 physical, 4 logical processors, but I am getting a 31%
> > improvement (netbench) when hyperthreading is enabled.  Thats
> > why I want to
> > confirm I am really only using 2 physical, 4 logical
> > processors.  Is there
> > any way I can do this? (dmesg? /proc/cpuinfo?)
>
> Well the two alternatives are, either A) turning on hyperthreading enabled
> the two virtual processors or B) turning on hyperthreading somehow enabled
> the other two processors, right?
>
> I would think B would be highly unlikely.
>
> Anyone else who actually has HT hardware care to comment? ;-)
>
> Regards -- Andy
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