1. In a graphics processing system, a method for selecting a command thread for processing, the method comprising: providing, by an input arbiter implemented by the graphics processing system, a plurality of pixel and vertex command threads to each of a first and second reservation station; selecting, by an arbiter implemented by the graphics processing system, a pixel command thread from the plurality of pixel command threads; selecting, by the arbiter, a vertex command thread from the plurality of vertex command threads; and selecting, by the arbiter as the command thread, either of the pixel command thread and the vertex command thread.