Posix Threads and Cpu affinity syscall

Hello,

in RH9 Kernel the sched_setaffinity() and sched_getaffinity() system 
calls are implemented. They have a per-process basis.
Now I need to associate a CPU of my SMP to a specific thread (NPTL).
This seems impossible because several threads have the same PID.
Can anyboby help Me?

Thanks.

		Mike-Ro-Chanel