2 Processors under FreeBSD 5.3

[Stephen Montgomery-Smith]

I have a dual Athlon MP computer, and I have a very recent version of 
FreeBSD 5.3 running on it.

If I start 6 computer intensive processes, and then kill 3 of them that 
are using (say) processor 1, then the other 3 processes are all 
processor 0, and as such only get 33% computer time each.

Under FreeBSD 4.10 they would have got 66% computer time each, because 
there each process didn't seem stuck to a particular processor.

Is there a sysctl variable that controls this, or is this a bug in 
FreeBSD 5.3, or what is going on?

Here is the computer intensive process:

main() {
   int i;
   while(1) {i++;}
}