roll up does not work in process chain

Hi expert,

          I have a infocube, get roll up in process chain by process type 'roll up filled aggregates/BWA indexes'. I can check out its running every day. but when I manage this infocube, all the loaded request do not have any roll up.  in process type , I set 'Roll up only those requests that were loaded xxx days ago' = 0. could you please tell me what is wrong this this roll up operation?

Many Thanks,

Bo