Re: Distinguish real vs. virtual CPUs?

[Daniel Andersen]

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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