1. A graphics processing unit (GPU) for determining whether to perform a tessellation operation on a first model of a plurality of prepared models according to a control of a central processing unit (CPU), comprising: an access circuit configured to read the first model from a memory, the memory storing the plurality of prepared models having different complexities, calculate a complexity of the first model, compare the calculated complexity with a reference complexity, and determine whether to perform a tessellation operation on the first model according to the comparison result.