tar using all cores with pigz

hopeless:~ # du -hs /lib
399M    /lib
hopeless:~ # time tar -cf lib_1.tar.gz /lib

real    0m55.562s
user    0m0.372s
sys     0m3.424s
hopeless:~ # time tar -cf lib_2.tar.gz -I pigz /lib

real    0m48.780s
user    0m34.028s
sys     0m2.808s
hopeless:~ # time GZIP='-9 -n' tar czf lib_3.tar.gz /lib

real    3m26.126s
user    3m24.668s
sys     0m1.712s
hopeless:~ # du -h lib_*
384M    lib_1.tar.gz
111M    lib_2.tar.gz
109M    lib_3.tar.gz