Rank based dynamic voltage and frequency scaling for tiled graphics processors

With increasing interest in sophisticated graphics capabilities in mobile systems, energy consumption of graphics hardware is becoming a major design concern in addition to the traditional performance enhancement criteria. Our study of various modern games substantiates the observation that the workload of games varies significantly with time and hence can benefit from dynamic voltage and frequency scaling (DVFS). Since visual quality of graphics applications is highly dependent on the rate at which frames are processed, it is important to devise a DVFS scheme that minimizes deadline misses due to inaccuracies in workload prediction. In this paper, we demonstrate that tiled-graphics renderers exhibit substantial advantages over immediate-mode renderers in obtaining access to frame parameters that help in enhancing the workload estimation accuracy. We also show that, operating at a finer granularity of “tiles” as opposed to “frames” allows early detection and corrective action in case of a mis-prediction. We propose an accurate workload estimation technique and two DVFS schemes: (i) tile-history based DVFS and (ii) tile-rank based DVFS for tiled-rendering architectures. The proposed schemes are demonstrated to be more efficient in terms of power and performance than the frame level DVFS schemes proposed in recent literature. With a system with 8 DVFS levels, our tile-history based DVFS scheme results in 60% improvement in quality (deadline misses) over the frame history based DVFS schemes and gives 58% saving in energy. The more sophisticated tile-rank based scheme achieves 75% improvement in quality over the frame history based DVFS scheme and results in 58% saving in energy. We have also compared the efficiency of the proposed tile-level DVFS schemes with frame-level schemes for different number of DVFS levels, and found that while the frame-level schemes suffer from increasing deadline misses as the frequency levels increase, the impact on tile-level schemes is negligible. The Energy per Frame-rate for our scheme is the minimum, indicating that it delivers the best performance-energy results.