If the Anonymous OP is confused by the logarithmic x-axis: for an equal distance along the x-axis, the x-value goes up by a constant factor. (So if the ticks were 1cm apart, and 10 is on the far left, then 1cm to the right of 10 is 100, and 1cm to the right of 100 is 1000: ie, every factor of 10 gets an equal amount of space on the x-axis). gnuplot labels the ticks, so it was unambiguous; however, not everyone has experience looking at a graph with a logarithmic x-axis, so the curve the OP saw might not be immediately identified in the OP's mind as linear.

If the OP wants a graph with a linear x-axis, then edit choroba's code by changing the following lines in sub plot { ...: change the lines here:

    print {$gp} join "\n", 'set term png;',
                           'set output "measure.png";',
                           'set key left;',
                           'set logscale x;';
[download]

    print {$gp} join "\n", 'set term png;',
                           'set output "measure.png";',
                           'set key left;';
    #                      'set logscale x;';
[download]

When I plotted with a linear x-axis, the curve for perl is almost perfectly straight -- I think that might communicate the idea to the OP with more clarity.