The requirements on the real-time control systems for ELT instruments strongly encourage an investigation of newly emerging hardware and an assessment of its suitability for the job. We have implemented the full AO data processing pipeline on Graphics Processing Units (GPUs), within the framework of Durham AO Real-time Controller (DARC). The pixel data are copied from the CPU memory to the GPU memory. On the GPU, the data are processed and the DM commands are copied back to the CPU. For a system of 80x80 subapertures, the highest rate achieved on a single GPU is 550 frames per second. When running on two or more GPUs, the kernel launching time limits the increase in frame rate. We have also implemented the correlation centroiding algorithm, which - when used - reduces the frame rate by about a factor of two.