Date: Tue, 22 Mar 2005 03:01:01 +0100
From: Daniel Andersen <anddan@linux-user.net>
Subject: Re: Distinguish real vs. virtual CPUs?
In-reply-to: <20050321202726.A7630@morpheus>
To: Dan Maas <dmaas@maasdigital.com>
Cc: linux-kernel@vger.kernel.org
Message-id: <423F7C5D.4000203@linux-user.net>
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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).
> 
> Please CC replies.
> 
> Thanks,
> Dan Maas
> -

The simplest thing to do would be to boot with the "noht" parameter.

Or you can use "schedtool" (google or freshmeat) to set the CPU-affinity 
at runtime to avoid HyperThreading the processes.

Daniel Andersen

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