use Benchmark qw( cmpthese );

cmpthese(-3, {
   'for' => sub {
      open(my $fh_in, '<', $0)
         or die("Unable to open input file: $!\n");
      my $infile_num_chunks = int((-s $fh_in) / 8);
      for ($chunk_counter = 0; $chunk_counter < $infile_num_chunks +1; ++$chunk_counter) {
         read($fh_in, my $data, 8);
         # ...
      }
      # ...
      1;
   },

   'while' => sub {
      open(my $fh_in, '<', $0)
         or die("Unable to open input file: $!\n");
      while (read($fh_in, my $data, 8) == 8) {
         # ...
      }
      # ...
      1;
   },
});