A graphics processing unit is configured to process graphics data using a rendering space which is sub-divided into a plurality of tiles. The graphics processing unit comprises one or more processing cores configured to process graphics data. The graphics processing unit also comprises cost indication logic configured to obtain a cost indication for each of a plurality of sets of one or more tiles of the rendering space, wherein the cost indication for a set of one or more tiles is suggestive of a cost of processing the set of one or more tiles. The graphics processing unit also comprises scheduling logic configured to schedule, in dependence upon the cost indications, the sets of one or more tiles for processing on the one or more processing cores.