Paris Game/AI Conference 2011
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Slides from the Paris Game/AI Conference 2011 talk by Neil Henning - covering the
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Paris Game/AI Conference 2011
- 1. Preparing AI for Parallelism Lessons from NASCAR The Game 2011 Neil Henning – Technology Lead Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 2. Introduction Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 3. Introduction I am sure some of you are wondering... Why a guy from is doing a talk about which was developed by Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 4. Introduction Team from Codeplay worked for 15 months on game Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 6. 43 cars on screen at the same time
- 7. Cars race in tight packs on the circuit
- 8. Overtaking is all about navigating through these packs Cannot simply make the AI use LODs, nearly always in view Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 9. Agenda Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 12. Why prepare your AI for parallelism?
- 13. What changes should be made?
- 14. What common issues are there?
- 15. How did these changes help when optimizing NASCAR?
- 16. How did we make use of the PS3's unique hardware? What performance improvement was achieved? Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 17. Why prepare your AI for parallelism? Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 19. Say we have four bots
- 20. In serial – can easily fit in a frameframe length Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 22. Have to either optimize or parallelize (or both)frame length Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 24. Only possible with parallelismframe length Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 26. This generation of consoles are multicore
- 27. Sony's new PS Vita is quad core
- 28. Even iPad usesdual core processors now!
- 29. Being able to split work amongst cores is key
- 30. Might not be required yet, but could be essential laterNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 32. Optimization being sought throughout engine
- 33. Either optimize engine or cut features
- 34. Have AI prepared to become parallel
- 35. Optimization folks will love you!Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 36. What changes should be made? Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 38. In NASCAR, had 18 components for each carDriving Controllers Stay Behind Obstacle Detection Stay Beside Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 40. All components in a group can be run in parallelNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 42. Each car’s groups can be run in parallel too0 1 2 … … 42 Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 44. Two phases for your AI
- 45. Read phase can read world/other car state
- 46. Write phase can modify own car stateNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 48. In read phase, store needed reads into temporary data
- 49. In write phase, read from the temporary data
- 50. AI is one frame behind world events
- 51. Effect on AI is minimalNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 54. Only components that required world/other car stateNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 59. Documenting the relationship saves time and effort laterNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 60. What common issues are there? Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 62. ~500-1200 cycles on PowerPC if virtual lookup misses cache
- 63. Can equate to a large amount of time doing no workNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 65. Based on previous game (Supercar Challenge)
- 66. 16 cars in previous, now 43 cars
- 67. 5 component types in previous, now 18 component types
- 68. Now read/write phase too
- 69. 80 virtual calls to update became 1333 virtual calls!Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 71. In real terms, 3ms of virtual function lookup per frame
- 72. First optimization was to have typed buckets of components
- 73. 1333 virtual calls went to 31 virtual calls
- 74. Platform agnostic (PS3, 360 and Wii all sped up)Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 76. Not knowing the size of data kills SPU/Compute developmentNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 78. Avoid/reduce/remove locks if possible
- 81. AI required knowledge of obstacles
- 82. Physics system used, raycast to find problematic obstacles
- 83. Each call to raycast used a mutex, every thread would halt!
- 84. Had to refactor code to remove need for lockingNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 86. How did these changes help when optimizing NASCAR? Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 88. Allowed work to be split across all 6 threads
- 89. Each thread was given 1/6th of the cars to process
- 90. Takes 2ms of all CPU resources on 360 in a frameNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 92. Only 2 threads on PS3, but have 6 sub processors (the SPUs)
- 93. Both threads on PS3 were completely full
- 95. How did these changes help when optimizing NASCAR? On PS3 most costly components were targeted Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 97. And all components in a group being able to be run in parallel
- 98. Costly groups were made to use the SPUs
- 99. Knowing relationship between data was key
- 100. Well documented code made life so much easier!Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 101. How did we make use of the PS3's unique hardware? Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 103. Very tight deadlines, 1 month to reduce time taken in AI
- 104. No main thread time left – have to use the SPUs
- 105. Our Offload compiler technology crucialNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 107. They are amazingly fast, if you code correctly for them
- 108. Normally requires total rewrite of existing codebase
- 109. Painful to access global variables
- 110. Virtual functions are a complete write offNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 112. Common to have 4-5 SPU programmers for ~10 months
- 113. Not feasible for late-in-cycle development
- 114. Offload aims to mitigate the issues with getting code onto SPU
- 115. Can offload code to SPU much quicker (typically a few man days)
- 116. Much easier to move existing code bases to SPUNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 118. Any work within an offload block is performed on the SPU
- 119. All PPU code is duplicated for the SPUNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 121. Just use them as normal!Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 123. Just have to specify which virtual functions may be calledNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 125. Four components taking most of the frame timeNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 128. How did we make use of the PS3's unique hardware? Stay Behind Other Car Stay Beside Other Car Looked at Stay Behind/Beside Other Car together In the same group, can be run in parallel Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 129. How did we make use of the PS3's unique hardware? Stay Behind Other Car Stay Beside Other Car Moved Stay Behind component to SPU Stay Beside component would continue to be run on PPU Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 130. How did we make use of the PS3's unique hardware? Stay Behind Other Car Stay Beside Other Car As long as SPU work was less time than the PPU work, no cost! Effectively ‘hid’ the cost of calculating Stay Behind component Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 133. Changes were purely optimizationAIObstacle** obstacles; unsigned intnumObstacles; offloadThread_thandle = __offload(obstacles, numObstacles) { for(unsigned int i = 0; i < numObstacles; i++) { AIObstacle* obstacle = obstacles[i]; // use obstacle for calculations } }; Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 135. Changes were purely optimization// array of AIObstacle* ’s on main memory AIObstacle** obstacles; unsigned intnumObstacles; offloadThread_thandle = __offload(obstacles, numObstacles) { for(unsigned int i = 0; i < numObstacles; i++) { // AIObstacle* points to main memory AIObstacle* obstacle = obstacles[i]; // use obstacle for calculations } }; Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 137. Changes were purely optimization// array of AIObstacle* ’s on main memory AIObstacle** obstacles; unsigned intnumObstacles; offloadThread_thandle = __offload(obstacles, numObstacles) { CachedPointer<AIObstacle*> innerObstacles(obstacles, numObstacles); for(unsigned int i = 0; i < numObstacles; i++) { // AIObstacle* points to main memory CachedPointer<AIObstacle> obstacle(innerObstacles[i]); // use obstacle for calculations } }; Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 138. What performance improvement was achieved? Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 140. ~100 lines of source code changed
- 141. 2½ weeks development timeNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 143. ~100 lines of source code changed
- 144. 2½ weeks development timeNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 146. ~50 lines of source code changed
- 147. 1 week development timeNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 149. ~50 lines of source code changed
- 150. 1 week development timeNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 152. ~20 lines of source code changed
- 153. 8 hours development timeNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 155. ~20 lines of source code changed
- 156. 8 hours development timeNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 158. 50% speed improvement on PS3Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 159. Takeaway Neil Henning neil@codeplay.com Paris Game AI Conference 2011
- 161. But need code ready to be parallelised
- 162. Small changes in coding style lead to hugely better results
- 163. Better to plan systems from beginning with multicore in mindNeil Henning neil@codeplay.com Paris Game AI Conference 2011
- 164. Questions? Can also catch me on twitter @sheredom Neil Henning neil@codeplay.com Paris Game AI Conference 2011