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SubjectRe: Distinguish real vs. virtual CPUs?
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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