Laptop not using all the CPU power

[Pafo]

I have i5-6200 and the turbo boost is up 2,80ghz. However when i click properties on My Computer,it shows 2,30, 2,40 so there are 0,40 ghz that i GUESS are not usable.Before showing 2,40 before it was 2,30, 2,30 so somehow i managed to upgrade or i don't know.Can someone explain me what is the problem or is there any problem, because i have very unstable fps.I will give an example:even playing hearthstone sometimes i have of course very high fps ultra smooth (i have geforce 940m) and sometimes i lags as hell.

 

[Killer MO]

The frequency is changing automatic. It' totally normal for a mobile version.