1. In a graphics processing system, a method for selecting a command thread for processing, the method comprising: selecting a command thread from either of a plurality of pixel command threads and a plurality of vertex command threads based on relative priorities of the plurality of pixel command threads and the plurality of vertex command threads, wherein selecting the command thread based on the relative priorities further comprises selecting the command thread based on specific commands that have been executed in any of the plurality of pixel command threads or any of the plurality of vertex command threads and selecting, as the command thread an oldest one of the plurality of pixel command threads and the plurality of vertex command threads; and providing the command thread to a command processing engine.