Date: Mon, 21 Mar 2005 20:56:03 -0500
From: Dave Jones <davej@redhat.com>
To: Dan Maas <dmaas@maasdigital.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Distinguish real vs. virtual CPUs?
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	Dan Maas <dmaas@maasdigital.com>, linux-kernel@vger.kernel.org
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On Mon, Mar 21, 2005 at 08:27:26PM -0500, Dan Maas wrote:
 > Is there a canonical way for user-space software to determine how many
 > real CPUs are present in a system (as opposed to HyperThreaded or
 > otherwise virtual CPUs)?
 > 
 > We have an application that for performance reasons wants to run one
 > process per CPU. However, on a HyperThreaded system /proc/cpuinfo
 > lists two CPUs, and running two processes in this case is the wrong
 > thing to do. (Hyperthreading ends up degrading our performance,
 > perhaps due to cache or bus contention).

Compare the 'physical id' fields of /proc/cpuinfo, and count
how many unique values you get.
Ie, on my dual+ht, I see..

physical id     : 0
physical id     : 0
physical id     : 3
physical id     : 3

Which indicates 2 real CPUs split in two.

		Dave

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