Surface Compression Using Dynamic Color Palettes

Abstract

Off-chip memory traffic is a major source of power and energy consumption on mobile platforms. A large amount of this off-chip traffic is used to manipulate graphics framebuffer surfaces. To cut down the cost of accessing off-chip memory, framebuffer surfaces are compressed to reduce the bandwidth consumed on surface manipulation when rendering or displaying. In this work, we study the compression properties of framebuffer surfaces and highlight the fact that surfaces from different applications have different compression characteristics. We use the results of our analysis to propose a scheme, Dynamic Color Palettes (DCP), which achieves higher compression rates with UI and 2D surfaces. DCP is a hardware mechanism for exploiting inter-frame coherence in lossless surface compression; it implements a scheme that dynamically constructs color palettes, which are then used to efficiently compress framebuffer surfaces. To evaluate DCP, we created an extensive set of OpenGL workload traces from 124 Android applications. We found that DCP improves compression rates by 91% for UI and 20% for 2D applications compared to previous proposals. We also evaluate a hybrid scheme that combines DCP with a generic compression scheme. We found that compression rates improve over previous proposals by 161%, 124% and 83% for UI, 2D and 3D applications, respectively.