on the concrete you could use self leveling but on floorboard using self level will crack/break away eventually from the moisture of the water in the self level compound hitting with the floorboard, wood would expand in the floorboards and wont perform a contact bond and will result in a poor finish, best bet would be to use marine ply and board the floor or start from scratch and rip the lot out, if its downstairs, why not take the floorboards up and refill with concrete, then shot a self level over the lot of it, to give a good finish.
just my opinion, might work might not