Hi Ram,
The CPU will be consumed as it is needed - there are no clear rules here. You are more likely to see problems in SM50 when a user tries, for example, to read too much data and is hogging a work process. That may cause system performance. Then it is a case of contacting the user to see what they were running and try and educate them to enter more selection criteria.
If the DB time gets too high relative to the processing time, then you might need to check whether the database is having perfornance issues and potentially move around the data files onto different disks.
Regards,
Graham