My understanding is that if the 'physical id' field is present in /proc/cpuinfo, it indicates the physical processor this hyperthreading processing is associated with. It's certainly there on 2.4.20-8smp as shipped by RedHat. It's possible they've patched the kernel for this, though, as I don't see it on a vanilla 2.5.70 machine I have.
Regards, Robert.
