taskset.

$taskset -p 1578
pid 1578's current affinity mask: 1
$

taskset is used to  retrive or set the processor affinity
mask of either an  existing process,given it's PID, or to
run  a  new  process,  given  it's  command  name,with  a
specified  affinity mask. The  Linux scheduler  will then
honor the  given affinity mask,ensuring  that the process
in question runs only on allowed processors.