davido:~/scripts$ perlbrew exec --with perl-5.10.1 perl mytest.pl
Perl version: 5.010001

          Rate retn bare
retn 6849315/s   --  -8%
bare 7462687/s   9%   --

(25000000, 25000000)


davido:~/scripts$ perlbrew exec --with perl-5.28.0 perl mytest.pl
Perl version: 5.028000

           Rate bare retn
bare 10729614/s   --  -3%
retn 11013216/s   3%   --

(25000000, 25000000)