/proc/[pid]/stat
 (39) processor  %d  (since Linux 2.2.8)
                        CPU number last executed on.

$ cat /proc/1185/task/1283/stat | awk '{print $39}'
-1

$ cat /proc/1283/stat | awk '{print $39}'
-1

$ cat /proc/1800/stat | awk '{print $39}'
17
$ cat /sys/devices/system/cpu/online
0-15
$ ps -eLo pid,psr | grep 1800
 1800  14

comm  %s
                        The filename of the executable, in parentheses.  This is  visible  whether  or
                        not the executable is swapped out.