Mantle for developers

1. Mantle for developers Johan Andersson – technical director Frostbite Electronic arts

2. Mantle? • Simplify advanced development • Improve performance • Enable developers to innovate • Challenge the status quo

4. Developer impact areas GPU performance CPU performance Control Platforms Programmability

5. Control New model Traditional Model: Black Box Explicit Model: Mantle • Middle-ground abstraction – compromise between performance & “usability” • Hidden resource memory & state • Resource CPU access tied to device context • Driver analyzes & synchronizes implicitly • Thin low-level abstraction to expose how hardware works • App explicit memory management • Resources are globally accessible • App explicit resource state transitions

6. Control App responsibility • Tell when render target will be used as a texture • And many more resource state transitions • Don’t destroy resources that GPU is using • Keep track with fences or frames • Manual dynamic resource renaming • No DISCARD for driver resource renaming • Resource memory tiling • Powerful validation layer will help!

7. Control Explicit control enables • App high-level decisions & optimizations • Has full scene information • Easier to optimize performance & memory • Flexible & efficient memory management • Linear frame allocators • Memory pools • Pinned memory • Reduced development time • For advanced game engines & apps • Easier to get to target performance & robustness

8. Control Explicit control enables • Light-weight driver • Easier to develop & maintain • Reduced CPU draw call overhead • Transient resources • Alias render targets within frame • Major memory savings • No need to pre-allocate everything

9. CPU performance Control

10. CPU perf Core concepts • Descriptor sets • Monolithic pipelines • Command buffers

11. Example 1: Single simple dynamic descriptor set Bind everything you need for a single draw call Close to DX/GL model but share between stages CPU perf Descriptor sets • Table with resource references to bind to graphics or compute pipeline • Replaces traditional resource stage binding • Major performance & flexibility advantage • Closer to how the hardware works • App managed - lots of strategies possible! • Tiny vs huge sets • Single vs multiple • Static vs semi-static vs dynamic Image Memory Link Sampler Dynamic descriptor set VertexBuffer (VS) Texture0 (VS+PS) Constants (VS) Texture1 (PS) Texture2 (PS) Sampler0 (VS+PS)

12. Example 2: Reuse static set with nesting Reduce update time & memory usage CPU perf Descriptor sets • Table with resource references to bind to graphics or compute pipeline • Replaces traditional resource stage binding • Major performance & flexibility advantage • Closer to how the hardware works • App managed - lots of strategies possible! • Tiny vs huge sets • Single vs multiple • Static vs semi-static vs dynamic Image Memory Dynamic descriptor set Link Sampler Static descriptor set Constants (VS) VertexBuffer (VS) Link Texture0 (VS+PS) Texture1 (PS) Texture2 (PS) Texture3 (PS) Texture4 (PS) Sampler0 (VS+PS) Sampler1 (PS)

13. CPU perf Monolithic pipelines • Shader stages & select graphics state combined into single object • No runtime compilation or patching needed! • Significantly less runtime overhead to use • Supports parallel building & caching • Fast loading times • Usage & management up to the app • Static vs dynamic creation • Amount of pipelines • State usage Pipeline state DB IA VS HS DS GS RS PS CB Tessellator

14. CPU perf Command buffers • Issue pipelined graphics & compute commands into a command buffer • Bind graphics state, descriptor sets, pipeline • Draw calls • Render targets • Clears • Memory transfers • NOT: resource mapping • Fully independent objects • Create multiple every frame • Or pre-build up front and reuse

15. CPU perf DX/GL parallelism Game Game Game CPU 0 Render Render Render CPU 1 Driver Render CPU 2 • Automatically extracts parallelism out of most apps  • Doesn’t scale beyond 2-3 cores  • Additional latency  • Driver thread often bottleneck – can collide app threads 

16. CPU perf Parallel dispatch with Mantle Game Game Game CPU 0 Render Render Render CPU 1 Render Render Render CPU 2 Render Render Render CPU 3 Render Render Render CPU 4 • App can go fully wide with its rendering – minimal latency  • Close to linear scaling with CPU cores  • No driver threads – no overhead – no contention  • Frostbite’s approach on all consoles – and on PC with Mantle! 

17. GPU performance CPU performance

18. Resource states Gives driver a lot more knowledge & flexibility Apps can avoid expensive/redundant transitions, such as surface decompression Expose existing GPU functionality Quad & Rect-lists HW-specific MSAA & depth data access Programmable sample patterns And more.. GPU perf GPU optimizations • Thanks to improved CPU performance – CPU will rarely be a bottleneck for the GPU • CPU could help GPU more: • Less brute force rendering • Improve culling • Shader pipeline object – driver optimizations • Can optimize with pipeline state knowledge • Can optimize across all shader stages

19. GPU perf Queues • Modern GPUs are heterogeneous machines with multiple engines • Graphics pipeline • Compute pipeline(s) • DMA transfer • Video encode/decode • More… • Mantle exposes queues for the engines + synchronization primitives Graphics Compute DMA . . . Queues GPU

20. GPU perf Queues Graphics Compute DMA . . . Queues GPU

21. GPU perf Queue use cases • Async DMA transfers • Copy resources in parallel with graphics or compute Copy DMA Render Other render Use copy Graphics

22. GPU perf Queue use cases • Async DMA transfers • Copy resources in parallel with graphics or compute • Async compute together with graphics • ALU heavy compute work at the same time as memory/ROP bound work to utilize idle units Compute Graphics Non-shadowed lighting GBuffer Shadowmap 0 Shadowmap 1 Final lighting

23. Multiple compute kernels collaborating Can be faster than über-kernel Example: Compute geometry backend & compute rasterizer GPU perf Queue use cases • Async DMA transfers • Copy resources in parallel with graphics or compute • Async compute together with graphics • ALU heavy compute work at the same time as memory/ROP bound work to utilize idle units Compute Geometry Compute 0 Compute Rasterizer Compute 1 Ordinary Rendering Graphics

24. Multiple compute kernels collaborating Can be faster than über-kernel Example: Compute geometry backend & compute rasterizer Compute as frontend for graphics pipeline Compute runs asynchronously ahead and prepares & optimizes geometry for graphics pipeline GPU perf Queue use cases • Async DMA transfers • Copy resources in parallel with graphics or compute • Async compute together with graphics • ALU heavy compute work at the same time as memory/ROP bound work to utilize idle units Process1 Process0 Compute Graphics Process0 • Game engines will build large GPU job graphs • Move away from single sequential submission • Just as we already have done on CPU Draw0 Draw1 Draw2

25. GPU performance Programmability

26. Programmability Explicit Multi-GPU • Explicit control of GPU queues and synchronization, finally! • Implement your own Alternate-Frame-Rendering • Or something more exotic.. • Use case: Workstation rendering with 4-8 GPUs • Super high-quality rendering & simulation • Load balance graphics & compute job graphs across GPUs • 20-40 TFlops in a single machine! • Use case: Low-latency rendering • Important for VR and competitive games • Latency optimized GPU job graph scheduling • VR: Simultaneously drive 2 GPUs (1 per eye)

27. Write occlusion query results into GPU buffer No CPU roundtrip needed Can drive predicated rendering Or use results directly in shaders (lens flares) Programmability New mechanisms • Command buffer predication & flow control • GPU affecting/skipping submitted commands • Go beyond DrawIndirect / DispatchIndirect • Advanced variable workloads • Advanced culling optimizations

28. Examples Performance optimizations – less data to update Logic & data structures that live fully on the GPU Scene culling & rendering Material representations Deferred shading Raytracing Programmability Bindless resources • Mantle supports bindless resources • Shaders can select resources to use instead of static binding from CPU • Extension of the descriptor set support • Key component that will open up a lot of opportunities!

29. Platforms Programmability

30. Platforms Today • Mantle gives us strong benefits on Windows today • Console-like performance & programmability on both Windows 7 and Windows 8 • For us, well worth the dev time! • DX & GL are the industry standards • Needed for platforms that do not support Mantle • Needed by devs who do not want/need more control • Have to have fallback paths for GL/DX, but not limit oneself to it • Mantle and PlayStation 4 will drive our future Frostbite designs & optimizations • PS4 graphics API has great programmability & performance as well • Share concepts, methods & optimization strategies

31. Platforms Linux & Mac • Want to see Mantle on Linux and Mac! • Would enable support for our full engine & rendering • Significantly easier to do efficient renderer with Mantle than with OpenGL • Use cases: • Workstations • R&D • Not limited by WDDM • Games • Mantle + SteamOS = powerful combination!

32. Platforms Mobile • Mobile architectures are getting closer in capabilities to desktop GPUs • Want graphics API that allows apps to fully utilize the hardware • Power efficient • High performance • Programmable • Major opportunity with Mantle – leap frog GL4, DX11 • For mobile SoC vendors • For Google and Apple

33. Platforms Multi-vendor? • Mantle is designed to be a thin hardware abstraction • Not tied to AMD’s GCN architecture • Forward compatible • Extensions for architecture- and platform-specific functionality • Mantle would be a much more efficient graphics API for other vendors as well • Most Mantle functionality can be supported on today’s modern GPUs • Want to see future version of Mantle supported on all platforms and on all modern GPUs! • Become an active industry standard with IHVs and ISVs collaborating • Enable us developers to innovate with great performance & programmability everywhere

34. Platforms

35. Frostbite Battlefield 4 • Mantle support is in development • Core renderer (closer to PS4 than DX11) • Implement all rendering techniques used in BF4 (many!) • CPU optimizations (parallel dispatch, descriptor sets) • GPU optimizations (minimize transitions, MSAA) • R&D for advanced GPU optimizations • Memory management • Multi-GPU support • ~2 months of work • Update targeting late December

36. Frostbite Plants vs Zombies: Garden Warfare • Very different rendering compared to BF4  • Frostbite Mantle renderer will work out of the box • Focus on APU performance

37. Frostbite Future • All Frostbite games designed with Mantle • 15 games in development across all of EA • Advanced Mantle rendering & use cases • Lots of exciting R&D opportunities! • Want multi-vendor & multi-platform support!

38. Email: repi@dice.se • Web: http://frostbite.com • Twitter: @repi The end