use Benchmark;

sub sub1    {   my $fh;
                open $fh, 'vsfull.csv';
                binmode $fh;

                my @lines;

                my $block; my $left = '';
                while( read $fh, $block, 8192 ){

                    $block = $left . $block;
                
                    my $i = index $block, "\n";
                    while($i > 0){
                    
                        push @lines, substr($block,0,$i);
                        substr($block,0,$i+1,'');
                        $i = index $block, "\n";

                    }

                    $left = $block;

                }
                
            }

sub sub2    {   my $fh;
                my @lines;
                open $fh, 'vsfull.csv';

                while(<$fh>){ push @lines, $_ };

            }

timethese( 100, { readbig  => \&sub1, whilelp  => \&sub2 });