$ cat a.pl; echo '-----------' ;echo;./a.pl 
#!/usr/local/bin/perl -w
           use Benchmark qw(:all) ;

our $s = join ' ', 'aa'..'zz';;
cmpthese( -3, { 
    split => q[ $_=$s; my $n = @{[ split ]}; ], 
    regex => q[ $_=$s; my $n = () = /\S+/g;  ] 
});

-----------

        Rate regex split
regex  981/s    --  -53%
split 2098/s  114%    --