Nope, that's not it

        # using regex
        'm//' => sub {
            my ( $first ) = $str =~ m/(.*?),/;
        },
        'm//s' => sub {
            my ( $first ) = $str =~ m/(.*?),/s;
        },
[download]

                  Rate        m//       m//s  split_unl  split_lim spl
+it_lim_sca
m//           486790/s         --        -3%       -17%       -17%    
+      -17%
m//s          499664/s         3%         --       -15%       -15%    
+      -15%
split_unl     585631/s        20%        17%         --        -0%    
+       -0%
split_lim     587555/s        21%        18%         0%         --    
+       -0%
split_lim_sca 587951/s        21%        18%         0%         0%    
+        --
[download]