Games are Up for DVFS

2. Games are Up for DVFS Yan Gu Samarjit Chakraborty Wei Tsang Ooi Department of Computer Science National University of Singapore

3. Outline • Goal of this work: • Explore the possibility of using DVFS for interactive games • Characterize the workload of game applications and use it to propose a DVFS scheme for games • Introduction • Anatomy of a Game Engine • A First Cut: Reduce Frame Rates • The Case for DVFS • DVFS for Games • Conclusion

4. Introduction • Popularity of interactive games on battery-powered portable devices (e.g. mobile phones, PDAs, PSP, etc.) • Voltage and frequency-scalable processors on portable devices • Can DVFS algorithms developed for video decoding applications be applied to games? • no interaction in video decoding, no buffering in games • We show that: • It is meaningful to use DVFS in the context of games • frame structure in game applications can be exploited to develop DVFS algorithms

5. Physics Particle Event Rendering Display AI DollisionDetection Computing Anatomy of a Game Engine

6. A First Cut: Reduce Frame Rates • Current game design principles: • higher frame rates imply the better game quality • Recent study on frame rates [Claypool et al. MMCN 2006] • very high frame rates are not necessary, very low frame rates impact the game quality severely

7. A First Cut: Reduce Frame Rates time Snapshots of animation[Davis et al. Eurographics 2003]

8. A First Cut: Reduce Frame Rates • Current game design principles: • higher frame rates imply the better game quality • Recent study on frame rates [Claypool et al. MMCN 2006] • very high frame rates are not necessary, very low frame rates impact the game quality severely • Obvious question: Can the CPU be run at a constant but lower frequency (to reduce the frame rate)?

9. A First Cut: Reduce Frame Rates desired frame rate

10. A First Cut: Reduce Frame Rates • Current game design • the higher frame rate, the better game quality • Recent study of frame rate • very high frame rates are not necessary, very low frame rates impact the game quality severely • Obvious question: Can the CPU be run at a constant but lower frequency (to reduce the frame rate)? • However, can DVFS algorithms developed for video decoding applications be applied to games? • unpredictable workload because of the interaction in game • no frame structure in video decoding

11. A First Cut: Reduce Frame Rates Average system-level power consumption for different processor frequencies

12. The Case for DVFSSnapshots of Game Maps “Outer Base” game map in Quake II “Installation” game map in Quake II

13. The Case for DVFSWorkload in Games • Game workload includes computational workload and rendering workload • correspondence with the complexity of the scene • Software renderer performs geometry, rasterization and texture processing on CPU • portable devices without graphics accelerator • Software rasterization workload is the workload of rasterizing objects on the screen • correspondence with the complexity of the scene

14. Computational workload Other workload Game workload Rendering workload Rasterization workload The Case for DVFSWorkload in Games

15. Computational workload Other workload Game workload Rendering workload Rasterization workload The Case for DVFSWorkload in Games Scene complexity

16. The Case for DVFSWorkload as a Function of Scene Complexity

17. The Case for DVFSWorkload Characterization • Each frame constitutes of the following objects: • brush model – construct the “world space” • Alias model – model characters like monsters, soldiers and weapons • texture – give the appearance of the brush model • light map – generate “lighting” effect • particles – model small debris from gun shots • ...

18. The Case for DVFSWorkload Characterization

19. The Case for DVFSWorkload Characterization • Each frame constitutes of the following objects: • brush model – construct the “world space” • Alias model – model characters like monsters, soldiers and weapons • texture – give the appearance of the brush model • light map – generate “lighting” effect • particles – model small debris from gun shots • ... • Computing workload of a frame: • Determine workload incurred in rasterizing each object offline • Determine the number of occurrences of each object online

20. The Case for DVFSBrush Model • Brush model • parameter: the number of polygons constitutingthe brush model

21. The Case for DVFSBrush Model • Brush model

22. The Case for DVFSAlias Model • Alias model • parameters: • the number of pixels of triangles • opaque or alpha blending mode of skin texture

23. The Case for DVFSAlias Model • Alias model

24. The Case for DVFSTexture, light map and particles • Texture • parameter: the number of surfaces • Light map • parameter: the number of surfaces • Particles • parameters: the number of pixels of 3D points Total rasterization workload = #cycles for brush X #brush models + #cycles for Alias X #Alias models + #cycles for texture X #textures + #cycles for light map X #light maps + #cycles for particle X #particles

25. DVFS for Games Poll player’s message Compute visible objects Obtain workload parameters of each object Game loop Online predict workload Compute required CPU frequency Scale to required CPU frequency Render the frame

26. DVFS for Games • Data structures to maintain the correlation between the workload parameters and the corresponding rasterization workload of each type of object • Linear regression model to find the fitting functions between the workload parameters and the corresponding rasterization workload for each type of object • Initial experiments show significant system-level power saving with our proposed framework

27. Conclusion • Explore the possibility of using DVFS for interactive games • Propose the workload characterization for games • Outline DVFS algorithms with our proposed workload characterization

28. Games are Up for DVFS Thank You!