CPU numbering & hyperthreading

[Andrew Athan <aathan_linux_kernel_1542@cloakmail.com>]

On an Intel Xeon dual CPU machine running 2.6.16 and up...

I have two highly CPU/memory/network intensive processes with 3-5 
threads each.  I am using sched_setaffinity calls to make sure these two 
processes never compete for the same physical CPU.  Am I right to assume 
that CPU #0 and #1 vs CPU #2 and #3 are separate physical CPUs on a 
2-CPU w/ hyperthreading box?

I've spent some time looking, but I did not find documentation on 
exactly how CPUs are numbered in a hyperthreaded box.

For a process with N threads where N is generally <=5, where each thread 
shares access to the same large (300Mb) data structure across several 
threads, and which pumps the data from memory to a TCP socket, making 
many futex, select, write(), send() network calls (but no disk I/O), I 
assume it is best to keep said process on the same physical CPU but 
allow use both logical processors on that CPU (vs. keeping it to a 
single logical CPU)?

Thanks,
A.