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In comp.os.linux.misc Orak Listalavostok suggested:
> Does anyone know how to determine if a given Linux machine is reporting
> real CPUs or hyperthreaded (ht) virtual CPUs?

> Using /proc/cpuinfo doesn't give any obvious difference.

It usually does, if ht is switched on, look for:

physical id :

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> From: hzmonte (hzmonte@hotmail.com)
> Subject: how do I know hyperthreading is enabled
> Newsgroups: comp.os.linux.misc
> Date: 2004-03-15 04:56:54 PST
>
> how do I know hyperthreading is enabled on any arbitrary Linux PC?

a) This should report the total number of physical CPUs:
grep -i "physical id" /proc/cpuinfo | sort -u | wc -l

b) This should report the total number of logical CPUs:
grep -i "processor" /proc/cpuinfo | sort -u | wc -l

c) The difference, is hyperthreaded.

Here is an annotated report from an IBM X335:
egrep -i "processor|physical id" /proc/cpuinfo
grep -E "processor|physical id" /proc/cpuinfo
which outputs (for example):
processor : 0 (CPU 0 is the first logical)
physical id : 0 (CPU 0 is the first physical)
processor : 1 (CPU 1 is the second logical)
physical id : 3 (CPU 3 is the second physical)
processor : 2 (CPU 2 is the third logical)
physical id : 0 (CPU 0 is the first physical)
processor : 3 (CPU 3 is the fourth logical)
physical id : 3 (CPU 3 is the second physical)

Orak

Orak Listalavostok wrote:
>>From: hzmonte (hzmonte@hotmail.com)
>>Subject: how do I know hyperthreading is enabled
>>Newsgroups: comp.os.linux.misc
>>Date: 2004-03-15 04:56:54 PST
>>
>>how do I know hyperthreading is enabled on any arbitrary Linux PC?
>
>
> a) This should report the total number of physical CPUs:
> grep -i "physical id" /proc/cpuinfo | sort -u | wc -l
>
> b) This should report the total number of logical CPUs:
> grep -i "processor" /proc/cpuinfo | sort -u | wc -l
>
> c) The difference, is hyperthreaded.
>
> Here is an annotated report from an IBM X335:
> egrep -i "processor|physical id" /proc/cpuinfo
> grep -E "processor|physical id" /proc/cpuinfo
> which outputs (for example):
> processor : 0 (CPU 0 is the first logical)
> physical id : 0 (CPU 0 is the first physical)
> processor : 1 (CPU 1 is the second logical)
> physical id : 3 (CPU 3 is the second physical)
> processor : 2 (CPU 2 is the third logical)
> physical id : 0 (CPU 0 is the first physical)
> processor : 3 (CPU 3 is the fourth logical)
> physical id : 3 (CPU 3 is the second physical)
>
> Orak
SCARY to use CPU second physical for two ....

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