make -j1

real    8m7.311s
user    7m41.999s
sys     0m37.994s
make -j2

real    4m33.848s
user    7m57.934s
sys     0m39.621s
make -j3

real    5m2.290s
user    8m3.572s
sys     0m40.139s
make -j4

real    3m44.131s
user    8m35.239s
sys     0m42.346s
make -j5

real    2m17.178s
user    9m48.592s
sys     0m47.305s
make -j6

real    2m2.187s
user    10m55.478s
sys     0m50.254s
make -j7

real    1m51.743s
user    11m55.338s
sys     0m54.332s
make -j8

real    1m46.199s
user    12m43.363s
sys     0m54.690s
make -j9

real    1m46.068s
user    12m45.576s
sys     0m55.415s
make -j10

real    1m46.169s
user    12m48.000s
sys     0m53.393s
make -j11

real    1m46.233s
user    12m50.974s
sys     0m52.545s
make -j12

real    1m46.400s
user    12m52.328s
sys     0m51.854s