I followed the procedure described in the below link to make the brightness function keys work on my Thinkpad X1 Extreme with Ubuntu 18.10 installed, however brightness does not correspond to the key press exactly. There are some delays. For example, pressing F6 five times and then F5 three times should increase and decrease the brightness level by 5 and 3 respectively. However, due to delays in response, pressing the keys do not corresponding well to changes in the screen brightness level. This is especially a problem if I press the two buttons continuously to adjust the brightness. Is there a way to fix this?