Okay, basically every process has a priority attached to it.. the default is 0. -20 is the most aggressive, (given the most CPU time) with 20 being the least (given the least CPU time). If all your processes are prioritized at 0 however (which they most likely will be unless you specify...
Remember, I'm getting this from a FreeBSD box, but since they both use OpenSSH it should work fine..
extracted from /etc/rc.network on FreeBSD..
/etc/rc.network: if [ ! -f /etc/ssh/ssh_host_key ]; then
/etc/rc.network: echo ' creating ssh RSA host key'...