Function not executed at all

I have a function called valvonta. I would like to run it every 6 secs. What is wrong here?

var toista_valvonta;
toista_valvonta = setTimeout(function() { valvonta }, 6000);

(function valvonta() {
alert('yes');
})();

Code (JavaScript):

 

var toista_valvonta;
function valvonta(){
toista_valvonta = setTimeout(valvonta, 6000);
   alert('yes');
}
valvonta();

Code (markup):