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OpenGL NVIDIA Command-List: Approaching Zero Driver Overhead

The document presents advancements in GPU command processing aimed at improving performance in graphics rendering, specifically through NVIDIA's nv_command_list technology. It discusses issues with traditional OpenGL commands, including high CPU workload and drawcall overhead, and proposes solutions such as tokenized rendering and bindless technology to reduce driver overhead and streamline the rendering pipeline. Performance demonstrations highlight significant improvements in drawcall throughput and GPU utilization using these new methods.

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Siggraph Asia 2014 Tristan Lorach Manager of Devtech for Professional Visualization group OPENGL NVIDIA "COMMAND-LIST": "APPROACHING ZERO DRIVER OVERHEAD"
2 Siggraph Asia 2014 GPU Scalability GPUs are extremely powerful But only if used correctly Mix of Application and Graphic API (Driver) responsibility Increase amount of work per batch (Job) Minimize CPUGPU interactions Lower Memory traffic Lower API calls: Batch things together Factorize Data Re-use data uploaded to Video memory (instancing…)
3 Siggraph Asia 2014 Use of the GPU Games ~1500 to 3000 Drawcalls for a scene Intensive use of Multi-layer image processing over the scene Heavy shaders CAD/FCC/professional applications Hard to batch user’s works (CAD applications) ~10,000 to… 300,000 Drawcalls for a scene: heavy CPU workload for our driver Shaders simpler than games (but catching-up these days...) Post-Processing more and more used (SSAO)
4 Siggraph Asia 2014 Use of the GPU New Graphic APIs are trying to address these concerns Khronos (Announced it at Siggraph Vancouver 2014) Metal Mantle DX12 All propose better ways to issue commands and render-states But can we improve OpenGL to go the same path ? Yes: NV_command_list
5 Siggraph Asia 2014 OpenGL OpenGL is ~25 years old (!!) 1.x: fixed function 2.x: Shading language (GLSL) 3.x/4.x: more as a massive compute system More graphic stages (Geom.Shader; Tessellation) High flexibility & efficiency on memory accesses High programability Design "flaws": still “State Machine”; ServerClient; poor multi-threading management 1992 2012
6 Siggraph Asia 2014 Challenge of Issuing Commands Issuing drawcalls and state changes can be a real bottleneck 650,000 Triangles 68,000 Parts ~ 10 Triangles per part 3,700,000 Triangles 98 000 Parts ~ 37 Triangles per part 14,338,275 Triangles/lines 300,528 drawcalls (parts) ~ 48 Triangles per part App + driver GPU GPU idle CPU Excessive Work from App & Driver On CPU ! ! courtesy of PTC
7 Siggraph Asia 2014 Big Picture – Typical Case Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Tr. Feedback buffer Uniform Block Texture Fetch Image Load/Store Atomic Counter Shader Storage Element buffer (EBO) Draw Indirect Buffer Vertex Buffer (VBO) Front-End (decoder) Cmd bundles OpenGL Driver Application Push-Buffer (FIFO) cmds FBO resources (Textures / RB) 64 bits pointers Handles (IDs) Id  64 bits Addr. OpenGL Commands OpenGL resources
8 Siggraph Asia 2014 Application Token-buffer OpenGL Driver Big Picture Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Tr. Feedback buffer Uniform Block Texture Fetch Image Load/Store Atomic Counter Shader Storage Element buffer (EBO) Draw Indirect Buffer Vertex Buffer (VBO) Front-End (decoder) Cmd bundles Push-Buffer (FIFO) cmds FBO resources (Textures / RB) OpenGL Commands resources 64 bits Pointers (bindless) 64 bits GPU Address Offload cmd bundles creation to the App.
9 Siggraph Asia 2014 Application Command-list Token-buffer OpenGL Driver Big Picture Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Tr. Feedback buffer Uniform Block Texture Fetch Image Load/Store Atomic Counter Shader Storage Element buffer (EBO) Draw Indirect Buffer Vertex Buffer (VBO) Front-End (decoder) Cmd bundles Push-Buffer (FIFO) cmds FBO resources (Textures / RB) OpenGL Commands Token-buffers + state objects resources 64 bits Pointers (bindless) State Object More work for FE – but fast !
10 Siggraph Asia 2014 Demo – Quadro K5000 CAD Car model 14,338,275 Primitives 300,528 drawcalls 348,862 attribute update 12,004 uniform update Set of CAD models together 29,344,075 Primitives 26,144 drawcalls 18,371 attribute update 13,632 uniform update
11 Siggraph Asia 2014 DemoS – Quadro K5000 CAD Car model K5000: 920,363,200 primitives/S 19,290,668 drawcalls/S
12 Siggraph Asia 2014 DemoS – Quadro K5000 Set of CAD models together K5000 1,211,684,096 primitives/S 1,079,545 drawcalls/S
13 Siggraph Asia 2014 DemoS – Maxwell CAD Car model K5000: 920,363,200 primitives/S 19,290,668 drawcalls/S Maxwell GM204 (GeForce): 1,782,257,920 primitives/S 37,355,848 drawcalls/S Drawcall time : 8 Micro- seconds on CPU (!) Set of CAD models together K5000 1,211,684,096 primitives/S 1,079,545 drawcalls/S Maxwell GM204 (GeForce) 3,012,795,392 primitives/S 2,684,239 drawcalls/S Drawcall time: 42 Micro- seconds on CPU !
14 Siggraph Asia 2014 More Performances Another test: always using bindless UBO and VBO CPU-Emulation: Token stream executed as CPU "switch-case" Strategies Un-grouped: ~ 1 MB, 79,000 Tokens, ~68,000 drawcalls Material-grouped: ~300 KB, 22,000 Tokens, ~11,000 drawcalls Strategy Draw time Material-grouped 0.73 HW TOKEN-Buffers 0.56 Technique GPU (ms) 1.4 1.14 x ~0 BIG x CPU (ms) Draw time un-grouped 2.4 1.1 GPU (ms) 4.5 1.6 x ~0 BIG x CPU (ms) CPU-emulated TOKEN-buffers glBindBufferRange + drawcalls 0.73 1.6 3.5 7.2 Preliminary results K6000
15 Siggraph Asia 2014 More Performances 5 000 shader changes: toggling between two shaders in „shaded & edges“ 5 000 fbo changes: similar as above but with fbo toggle instead of shader Almost no additional cost compared to rendering without fbo changes Timing GPU (ms) CPU (ms) CPU-emulated TOKEN-buffers 12.7 15.1 2.9 4.3 x 0.4 37 x HW TOKEN-buffers 2.8 4.5 x 0.005 BIG x Command-Lists Timer GPU (ms) CPU (ms) CPU-emulated TOKEN-buffers 60.0 60.0 1.8 33 x 0.9 66 x HW TOKEN-buffers 1.7 35 x 0.022 BIG x Command-Lists Preliminary results on K5000
16 Siggraph Asia 2014 GPU Virtual Memory Bindless Technology What is it about? Work from native GPU pointers/handles (NVIDIA pioneered this technology) A lot less CPU work (memory hopping, validation...) Allow GPU to use flexible data structures Bindless Buffers Vertex & Global memory since Tesla Generation (CUDA capable) Bindless Textures Since Kepler Bindless Constants (UBO) New driver feature, support for Fermi and above Bindless plays a central role for Command-List Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Uniform Block Texture Fetch Element buffer (EBO) Vertex Buffer (VBO) Front-End (decoder) Push buffer 64 bits address Attr.s Idx Uniform Block Send Ptrs
17 Siggraph Asia 2014 #define UBA UNIFORM_BUFFER_ADDRESS_NV UpdateBuffers(); glEnableClientState(UNIFORM_BUFFER_UNIFIED_NV); glBufferAddressRangeNV (UBA, 0, addrView, viewSize); foreach (obj in scene) { ... // glBindBufferRange (UBO, 1, uboMatrices, obj.matrixOffset, maSize); glBufferAddressRangeNV(UBA, 1, addrMatrices + obj.matrixOffset, maSize); foreach ( batch in obj.primitive_group_material) { // glBindBufferRange (UBO, 2, uboMaterial, batch.materialOffset, mtlSize); glBufferAddressRangeNV(UBA, 2, addrMaterial + batch.materialOffset, mtlSize); ... } } Example On Using Bindless UBO New pointer for UBO#1 updated per Object New pointer for UBO#2 updated per Primitive group pointer for UBO#0 updated once for all objects regular UBO binds are now ignored!
18 Siggraph Asia 2014 Pointers must be aligned So do Ptr Offsets glGetIntegerv(GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT, &offsetAlignment); Normally: 256 bytes  gaps between each item Try to fit as much data as possible… Not the case if passing an index for array access (MDI + “Base-instance”) But requires special GLSL code (indexing) Bindless And Memory Alignement GPU Virtual Memory 64 bits address Uniform Material 0 Uniform Material 1 Uniform Material 2 … glBufferAddressRangeNV (UBA, 2, addrMaterial + batch.materialOffset , mtlSize); 256b Uniform array materials[] Material 0 Material 1 Material 2 … Uniform …
19 Siggraph Asia 2014 NV_command_list Key Concepts 1.Tokenized Rendering: some state changes and draw commands are encoded into binary data stream Depends on bindless technology 2.State Objects Whole OpenGL States (program, blending...) captured as an object Allows pre-validation of state combinations, later reuse of objects is very fast 3.Command List Object „Display-list“ paradigm but more flexible: buffer are outside (referenced by address), so content can still be modified (matrics, vertices...)
20 Siggraph Asia 2014 UpdateBuffers(); glBindBufferBase (UBO, 0, uboView); foreach (obj in scene) { // redundancy filter for these (if (used != last)... glBindVertexBuffer (0, obj.geometry->vbo, 0, vtxSize); glBindBuffer (ELEMENT, obj.geometry->ibo); glBindBufferRange (UBO, 1, uboMatrices, obj.matrixOffset, maSize); // iterate over cached material groups foreach ( batch in obj.materialGroups) { glBindBufferRange (UBO, 2, uboMaterial, batch.materialOffset, mtlSize); glMultiDrawElements (...); } } Typical Scene Drawing Example ~ 2 500 api drawcalls ~11 000 drawcalls ~55 triangles per call
21 Siggraph Asia 2014 UpdateBuffers(); glBindBufferBase (UBO, 0, uboView); foreach (obj in scene) { // redundancy filter for these (if (used != last)... glBindVertexBuffer (0, obj.geometry->vbo, 0, vtxSize); glBindBuffer (ELEMENT, obj.geometry->ibo); glBindBufferRange (UBO, 1, uboMatrices, obj.matrixOffset, maSize); // iterate over all parts individually foreach ( part in obj.parts) { if (part.material != lastMaterial){ glBindBufferRange (UBO, 2, uboMaterial, part.materialOffset, mtlSize); } glDrawElements (...); } } Typical Scene Drawing Example ~68 000 drawcalls ~10 triangles per call
22 Siggraph Asia 2014 Scene Drawing Converted To Token Buffer glDrawCommandsNV (GL_TRIANGLES, tokenBuffer , offsets[], sizes[], count); // {0}, {bufferSize}, 1 foreach (obj in scene) { glBufferAddressRangeNV(VERTEX.., 0, obj.geometry->addrVBO, ...); glBufferAddressRangeNV(ELEMENT..., 0, obj.geometry->addrIBO, ...); glBufferAddressRangeNV(UNIFORM..., 1, addrMatrices ...); foreach ( batch in obj.materialGroups) { glBufferAddressRangeNV(UNIFORM, 2, addrMaterial ...); glMultiDrawElements(...) } } becomes a single drawcall replaces 80k calls to GL (for graphic-card model) Token buffer Set Attr#0 on VBO address … Set Attr#1 on VBO address … Set Elements on EBO address … Uniform Matrix on UBO address … Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Obj#1 Obj#2 … For all objects …
23 Siggraph Asia 2014 Tokens-buffers are tightly packed structs in linear memory Token Buffer Structures TokenUbo { GLuint header; UniformAddressCommandNV { GLushort index; GLushort stage; GLuint64 address; } cmd; } TokenVbo { GLuint header; AttributeAddressCommandNV { GLuint index; GLuint64 address; } cmd; } TokenIbo { GLuint header; ElementAddressCommandNV { GLuint64 address; GLuint typeSizeInByte; } cmd; } TokenDrawElements { Gluint header; DrawElementsCommandNV { GLuint count; GLuint firstIndex; GLuint baseVertex; } cmd; } Token buffer Set Attr#0 on VBO address … Set Attr#1 on VBO address … Set Elements on EBO address … Uniform Matrix on UBO address … Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements … Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements
24 Siggraph Asia 2014 Tokenized Rendering Token Headers are GPU commands, followed by arguments FRONTFACE_COMMAND_NV BLEND_COLOR_COMMAND_NV STENCIL_REF_COMMAND_NV LINE_WIDTH_COMMAND_NV POLYGON_OFFSET_COMMAND_NV ALPHA_REF_COMMAND_NV VIEWPORT_COMMAND_NV SCISSOR_COMMAND_NV ELEMENT_ADDRESS_COMMAND_NV ATTRIBUTE_ADDRESS_COMMAND_NV UNIFORM_ADDRESS_COMMAND_NV DRAW_ELEMENTS_COMMAND_NV DRAW_ARRAYS_COMMAND_NV DRAW_ELEMENTS_STRIP_COMMAND_NV DRAW_ARRAYS_STRIP_COMMAND_NV DRAW_ELEMENTS_INSTANCED_COMMAND_NV DRAW_ARRAYS_INSTANCED_COMMAND_NV TERMINATE_SEQUENCE_COMMAND_NV NOP_COMMAND_NV Final list might change Render States Index Buffer; Position Attribute; Normals; Texcoords... Matrices; Material data... Draw Commands ! Special Commands (see later)
25 Siggraph Asia 2014 Tokenized Rendering Example: UBO Address assignment structure FRONTFACE_COMMAND_NV BLEND_COLOR_COMMAND_NV STENCIL_REF_COMMAND_NV LINE_WIDTH_COMMAND_NV POLYGON_OFFSET_COMMAND_NV ALPHA_REF_COMMAND_NV VIEWPORT_COMMAND_NV SCISSOR_COMMAND_NV ELEMENT_ADDRESS_COMMAND_NV ATTRIBUTE_ADDRESS_COMMAND_NV UNIFORM_ADDRESS_COMMAND_NV DRAW_ELEMENTS_COMMAND_NV DRAW_ARRAYS_COMMAND_NV DRAW_ELEMENTS_STRIP_COMMAND_NV DRAW_ARRAYS_STRIP_COMMAND_NV DRAW_ELEMENTS_INSTANCED_COMMAND_NV DRAW_ARRAYS_INSTANCED_COMMAND_NV TERMINATE_SEQUENCE_COMMAND_NV NOP_COMMAND_NV TokenUbo { GLuint header; UniformAddressCommandNV { GLushort index; GLushort stage; GLuint64 address; } cmd; } Example Real Token to be queried header = glGetCommandHeaderNV( UNIFORM_ADDRESS_COMMAND_NV, Sizeof(TokenUbo) ) One Shading stage to target (not ‘program’) Stage = glGetStageIndexNV(S) (S: STAGE_VERTEX|GEOMETRY|FRAGMENT|TESS_CONTROL/EVAL) Hardware Index *not* Uniform Program index
26 Siggraph Asia 2014 TOKENIZED RENDERING Allows rendering of a mix of LIST, STRIP, FAN, LOOP modes in one go Pass „basic type“ as Token, use „mode“ for more in "Instanced" drawing TokenDrawElements { Gluint header; DrawElementsCommandNV { GLuint count; GLuint firstIndex; GLuint baseVertex; } cmd; } TokenDrawElementsInstanced { Gluint header; DrawElementsInstancedCommandNV { GLuint mode; GLuint count; GLuint instanceCount; GLuint firstIndex; GLuint baseVertex; GLuint baseInstance; } cmd; } LIST, STRIP, FAN, LOOP types (GL_LINE_LOOP...) DRAW_ELEMENTS_COMMAND_NV DRAW_ARRAYS_COMMAND_NV DRAW_ELEMENTS_STRIP_COMMAND_NV DRAW_ARRAYS_STRIP_COMMAND_NV glGetCommandHeaderNV() DRAW_ELEMENTS_INSTANCED_COMMAND_NV DRAW_ARRAYS_INSTANCED_COMMAND_NV glGetCommandHeaderNV()
27 Siggraph Asia 2014 TERMINATE_SEQUENCE: Occlusion Culling Now overcomes deficit of previous methods http://on-demand.gputechconf.com/gtc/2014/presentations/S4379-opengl-44-scene-rendering- techniques.pdf Enqueue all tokens for entire object Shader to Check Visibility; Shader for SCAN operation; Add TERMINATE_SEQUENCE_COMMAND_NV to end Technique Draw time GROUPED Timing GPU (ms) CPU (ms) 6.3 2.6 x 0.9 6 x CULL Old Bindless MDI (*) CULL NEW TOKEN native 0.2 27 x glBindBufferRange + drawcalls 16.8 5.4 6.2 2.7 x 6.3 0.85 x CULL Old Readback (stalls pipe) (*) K5000, Preliminary results, (*) taken from slightly differnt framework HW TOKEN-buffers ~0 BIG x No instancing! (synthetic test, data replication) SCENE: materials: 138 objects: 13,032 geometries: 3,312 parts: 789,464 triangles: 29,527,840 vertices: 27,584,376 16.8 5.3 3.1 x
28 Siggraph Asia 2014 Just a little... “commandBindableNV” turns binding IDs to Hardware IDs Texturing must go through bindless ARB_bindless_texture Regular Texture binding Turned Off Changing UBO Ptr Addresses == texture changes (here ‘myBuf’) Does Shaders Need Special Code ? #extension GL_ARB_bindless_texture : require #extension GL_NV_command_list : enable #if GL_NV_command_list layout(commandBindableNV) uniform; #endif layout(std140,binding=2) uniform myBuf { sampler2D mySampler; //or: in int whichSampler; }; layout(std140,binding=1) uniform samplers { sampler2D allSamplers[NUM_TEXTURES]; }; … c = texture(mySampler, tc); //or c = texture(allSamplers [ whichSampler ] , tc); … Example:
29 Siggraph Asia 2014 State Objects StateObject Encapsulates majority of state (fbo format, active shader, blend, depth ...) State Object immutable: gives more control over validation cost no bindings captured: bindless used instead; textures passed via UBO Primitive type is a state: participates to important validation work Cannot be put in the token buffer glCaptureStateNV(stateobject, GL_TRIANGLES ); Primitive type as argument: because it is part of states
30 Siggraph Asia 2014 Render entire scenes with different shaders/fbos... in one go Driver caches state transitions ! Draw With State Objects glDrawCommandsStatesNV( tokenBuffer, offsets[], sizes[], states[], fbos[], count); Token buffer VBO address … VBO address … EBO address … Uniform Matrix Uniform Material DrawElements Uniform Material DrawElements … EBO address … Uniform Matrix Uniform Material DrawElements Uniform Material DrawElements FBO 1 FBO 2 fbos[] FBO 1 FBO 1 State Obj 1 State Obj 2 State Obj 1 State Obj 4 Count = 4 States[] offsets[] sizes[0] sizes[1] sizes[2] sizes[3]
31 Siggraph Asia 2014 Driver bakes „Diff“ between states and apply only the difference Pseudo Code of glDrawCommandsStatesNV for i < count { if (i == 0) set state from states[i]; else set state transition states[i-1] to states[i] if (fbo[i]) { // fbo[i] must be compatible with states[i].fbo glBindFramebuffer( fbo[i] ) } else glBindFramebuffer( states[i].fbo ) ProcessCommandSequence(...tokenBuffer, offsets[i], sizes[i]) }
32 Siggraph Asia 2014 Rendering must always happen in a FBO Backbuffer Ptr. Address is un-reliable (dynamic re-alloc when resizing…) Use glBlitFramebuffer() for FBO  final Backbuffer result FBO Resources Must be Resident (glMakeTextureHandleResidentARB()) Resources can be replaced/swapped if they keep the same base configuration (attachment formats, # drawbuffers...) I.e. Same configuration as captured FBO settings from stateobject This is what happens when resizing: Detach & Destroy resource  create new ones  attach them to FBO(s) Frame-Buffer Objects And State Objects
33 Siggraph Asia 2014 Combine multiple token buffers & states into a CommandList object glCreateCommandListsNV(N, &list) glCommandListSegmentsNV(list, segs) Convenient for concatenation glListDrawCommandsStatesClientNV(list, segment, token-buffer-ptrs, token-buffer- sizes, states, FBOs, count) glCompileCommandListNV(list); glCallCommandListNV(list) Command-List Object System mem. VBO address … VBO address … EBO address … Uniform Matrix Uniform Material DrawElements … Uniform Material DrawElements FBO State Object System mem. VBO address … VBO address … EBO address … Uniform Matrix Uniform Material DrawElements … FBO State Object System mem. VBO address … VBO address … Uniform Matrix Uniform Material DrawArrays … Uniform Material DrawArrays FBO State Object … Command-List Segment #0 Segment #1
34 Siggraph Asia 2014 Command-List Object Less flexibilty compared to token buffer Token buffers taken from client pointers (CPU memory) Driver will optimize these token buffers and related state-objects Optimize State transitions; token cmds for the GPU Front-End Resulting command-list is immutable If any resource pointer changed, the command-list must be recompiled But still rather flexible possible to change content of referenced buffers! (matrices, materials, vertices...) Animation; skinning... No need for command-list recompilation
35 Siggraph Asia 2014 Command-List doesn’t pretend to solve any OpenGL multi-threading Multi-threading can help if complex CPU work going-on update of Vertex / Element buffers: transform. Matrices; skinning… Update of Token Buffers: adding/removing characters in a game scene… OpenGL & Multithreading issues: OpenGL is bad at sharing its access from various threads Make-Current or Multiple Contexts aren’t good solutions Prefer to keep context ownership to one main thread OpenGL And Multi-threading ?
36 Siggraph Asia 2014 Token Buffers and Vertex/Elements/Uniform Buffers (VBO/UBO) Token Buffer Objects; VBOs and UBOs owned by OpenGL Multi-threading can be used for data update if: Work on CPU system memory; then push data back to OpenGL (glBufferSubData) Or Request for a pointer (glMapBuffers); then work with it from the thread State Objects: State Object and their 'Capture' must be handled in OpenGL context No way to do it on a separate threads that don’t have OpenGL context Multi-threading And Command-List
37 Siggraph Asia 2014 Multi-threading Use-Case Example #1 Thread #0 OpenGL Ctxt Thread #1 Thread #1 Submit States PushAttrib() set states & and capture PopAttribs() Get State ID PushAttrib() set states & and capture PopAttribs() Submit States unmap Token buf. ask for Token buf. Ptr Build state list ask for Token buf. Ptr unmap Token buf. Build token cmds Get State ID Build token cmds Build token cmds ask for Token buf. Ptr unmap Token buf. ask for Token buf. Ptr ... ask for Token buf. Ptr Build token cmds unmap Token buf. Build token cmds Build state list
38 Siggraph Asia 2014 Multi-threading Use-Case Example #2 Split state capture from Token-buffer creation Thread 1 Thread 2 Thread 3 Build Token buffers in CPU memory Thread 0 OpenGL Ctxt Walk through whole scene and build State-Objects Receive Token-Buffers and issue them as Token Buffer Objects to OpenGL
39 Siggraph Asia 2014 Migration Steps All rendering via FBO (statecapture doesn‘t support default backbuffer) No legacy states in GLSL use custom uniforms no built-in uniforms (gl_ModelView...) use glVertexAttribPointer (no glTexCoordPointer etc.) No classic uniforms, pack them all in UBO ARB_bindless_texture for texturing Bindless Buffers ARB_vertex_attrib_binding combined with NV_vertex_buffer_unified_memory (VBUM)... Organize for StateObject reuse state capture expensive: Capture them at init. time; Factorize their use in the scene
40 Siggraph Asia 2014 Migration Tips Vertex Attributes and bindless VBO http://on-demand.gputechconf.com/siggraph/2014/presentation/SG4117- OpenGL-Scene-Rendering-Techniques.pdf (slide 11-16) GLSL // classic attributes ... normal = gl_Normal; gl_Position = gl_Vertex; // generic attributes // ideally share this definition across C and GLSL #define VERTEX_POS 0 #define VERTEX_NORMAL 1 in layout(location= VERTEX_POS) vec4 attr_Pos; in layout(location= VERTEX_NORMAL) vec3 attr_Normal; ... normal = attr_Normal; gl_Position = attr_Pos;
41 Siggraph Asia 2014 Migration Tips UBO Parameter management http://on-demand.gputechconf.com/siggraph/2014/presentation/SG4117- OpenGL-Scene-Rendering-Techniques.pdf ( 18-27, 44-47) Ideally group by frequency of change // classic uniforms uniform samplerCube viewEnvTex; uniform vec4 materialColor; uniform sampler2D materialTex; ... // UBO usage, bindless texture inside UBO, grouped by change layout(std140, binding=0, commandBindableNV) uniform view { samplerCube texViewEnv; }; layout(std140, binding=1, commandBindableNV) uniform material { vec4 materialColor; sampler2D texMaterialColor; }; ...
42 Siggraph Asia 2014 OpenGL Devtech 'Proviz' samples soon available on GitHub ! check https://github.com/nvpro-samples on a regular basis working on ramping-up https://developer.nvidia.com/samples & https://developer.nvidia.com/professional-graphics command-lists examples to come here this Dec. 2014 Many other samples will be pushed here as standalone repositories Beta Driver for Command-Lists: Release 346 for Dec.2014 Special Thanks to Pierre Boudier and Christoph Kubisch Questions/Feedback: tlorach@nvidia.com / ckubisch@nvidia.com Thanks!

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OpenGL NVIDIA Command-List: Approaching Zero Driver Overhead

  • 1.
    Siggraph Asia 2014 Tristan Lorach Manager of Devtech for Professional Visualization group OPENGL NVIDIA "COMMAND-LIST": "APPROACHING ZERO DRIVER OVERHEAD"
  • 2.
    2 Siggraph Asia2014 GPU Scalability GPUs are extremely powerful But only if used correctly Mix of Application and Graphic API (Driver) responsibility Increase amount of work per batch (Job) Minimize CPUGPU interactions Lower Memory traffic Lower API calls: Batch things together Factorize Data Re-use data uploaded to Video memory (instancing…)
  • 3.
    3 Siggraph Asia2014 Use of the GPU Games ~1500 to 3000 Drawcalls for a scene Intensive use of Multi-layer image processing over the scene Heavy shaders CAD/FCC/professional applications Hard to batch user’s works (CAD applications) ~10,000 to… 300,000 Drawcalls for a scene: heavy CPU workload for our driver Shaders simpler than games (but catching-up these days...) Post-Processing more and more used (SSAO)
  • 4.
    4 Siggraph Asia2014 Use of the GPU New Graphic APIs are trying to address these concerns Khronos (Announced it at Siggraph Vancouver 2014) Metal Mantle DX12 All propose better ways to issue commands and render-states But can we improve OpenGL to go the same path ? Yes: NV_command_list
  • 5.
    5 Siggraph Asia2014 OpenGL OpenGL is ~25 years old (!!) 1.x: fixed function 2.x: Shading language (GLSL) 3.x/4.x: more as a massive compute system More graphic stages (Geom.Shader; Tessellation) High flexibility & efficiency on memory accesses High programability Design "flaws": still “State Machine”; ServerClient; poor multi-threading management 1992 2012
  • 6.
    6 Siggraph Asia2014 Challenge of Issuing Commands Issuing drawcalls and state changes can be a real bottleneck 650,000 Triangles 68,000 Parts ~ 10 Triangles per part 3,700,000 Triangles 98 000 Parts ~ 37 Triangles per part 14,338,275 Triangles/lines 300,528 drawcalls (parts) ~ 48 Triangles per part App + driver GPU GPU idle CPU Excessive Work from App & Driver On CPU ! ! courtesy of PTC
  • 7.
    7 Siggraph Asia2014 Big Picture – Typical Case Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Tr. Feedback buffer Uniform Block Texture Fetch Image Load/Store Atomic Counter Shader Storage Element buffer (EBO) Draw Indirect Buffer Vertex Buffer (VBO) Front-End (decoder) Cmd bundles OpenGL Driver Application Push-Buffer (FIFO) cmds FBO resources (Textures / RB) 64 bits pointers Handles (IDs) Id  64 bits Addr. OpenGL Commands OpenGL resources
  • 8.
    8 Siggraph Asia2014 Application Token-buffer OpenGL Driver Big Picture Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Tr. Feedback buffer Uniform Block Texture Fetch Image Load/Store Atomic Counter Shader Storage Element buffer (EBO) Draw Indirect Buffer Vertex Buffer (VBO) Front-End (decoder) Cmd bundles Push-Buffer (FIFO) cmds FBO resources (Textures / RB) OpenGL Commands resources 64 bits Pointers (bindless) 64 bits GPU Address Offload cmd bundles creation to the App.
  • 9.
    9 Siggraph Asia2014 Application Command-list Token-buffer OpenGL Driver Big Picture Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Tr. Feedback buffer Uniform Block Texture Fetch Image Load/Store Atomic Counter Shader Storage Element buffer (EBO) Draw Indirect Buffer Vertex Buffer (VBO) Front-End (decoder) Cmd bundles Push-Buffer (FIFO) cmds FBO resources (Textures / RB) OpenGL Commands Token-buffers + state objects resources 64 bits Pointers (bindless) State Object More work for FE – but fast !
  • 10.
    10 Siggraph Asia2014 Demo – Quadro K5000 CAD Car model 14,338,275 Primitives 300,528 drawcalls 348,862 attribute update 12,004 uniform update Set of CAD models together 29,344,075 Primitives 26,144 drawcalls 18,371 attribute update 13,632 uniform update
  • 11.
    11 Siggraph Asia2014 DemoS – Quadro K5000 CAD Car model K5000: 920,363,200 primitives/S 19,290,668 drawcalls/S
  • 12.
    12 Siggraph Asia2014 DemoS – Quadro K5000 Set of CAD models together K5000 1,211,684,096 primitives/S 1,079,545 drawcalls/S
  • 13.
    13 Siggraph Asia2014 DemoS – Maxwell CAD Car model K5000: 920,363,200 primitives/S 19,290,668 drawcalls/S Maxwell GM204 (GeForce): 1,782,257,920 primitives/S 37,355,848 drawcalls/S Drawcall time : 8 Micro- seconds on CPU (!) Set of CAD models together K5000 1,211,684,096 primitives/S 1,079,545 drawcalls/S Maxwell GM204 (GeForce) 3,012,795,392 primitives/S 2,684,239 drawcalls/S Drawcall time: 42 Micro- seconds on CPU !
  • 14.
    14 Siggraph Asia2014 More Performances Another test: always using bindless UBO and VBO CPU-Emulation: Token stream executed as CPU "switch-case" Strategies Un-grouped: ~ 1 MB, 79,000 Tokens, ~68,000 drawcalls Material-grouped: ~300 KB, 22,000 Tokens, ~11,000 drawcalls Strategy Draw time Material-grouped 0.73 HW TOKEN-Buffers 0.56 Technique GPU (ms) 1.4 1.14 x ~0 BIG x CPU (ms) Draw time un-grouped 2.4 1.1 GPU (ms) 4.5 1.6 x ~0 BIG x CPU (ms) CPU-emulated TOKEN-buffers glBindBufferRange + drawcalls 0.73 1.6 3.5 7.2 Preliminary results K6000
  • 15.
    15 Siggraph Asia2014 More Performances 5 000 shader changes: toggling between two shaders in „shaded & edges“ 5 000 fbo changes: similar as above but with fbo toggle instead of shader Almost no additional cost compared to rendering without fbo changes Timing GPU (ms) CPU (ms) CPU-emulated TOKEN-buffers 12.7 15.1 2.9 4.3 x 0.4 37 x HW TOKEN-buffers 2.8 4.5 x 0.005 BIG x Command-Lists Timer GPU (ms) CPU (ms) CPU-emulated TOKEN-buffers 60.0 60.0 1.8 33 x 0.9 66 x HW TOKEN-buffers 1.7 35 x 0.022 BIG x Command-Lists Preliminary results on K5000
  • 16.
    16 Siggraph Asia2014 GPU Virtual Memory Bindless Technology What is it about? Work from native GPU pointers/handles (NVIDIA pioneered this technology) A lot less CPU work (memory hopping, validation...) Allow GPU to use flexible data structures Bindless Buffers Vertex & Global memory since Tesla Generation (CUDA capable) Bindless Textures Since Kepler Bindless Constants (UBO) New driver feature, support for Fermi and above Bindless plays a central role for Command-List Vertex Puller (IA) Vertex Shader TCS (Tessellation) TES (Tessellation) Tessellator Geometry Shader Transform Feedback Rasterization Fragment Shader Per-Fragment Ops Framebuffer Uniform Block Texture Fetch Element buffer (EBO) Vertex Buffer (VBO) Front-End (decoder) Push buffer 64 bits address Attr.s Idx Uniform Block Send Ptrs
  • 17.
    17 Siggraph Asia2014 #define UBA UNIFORM_BUFFER_ADDRESS_NV UpdateBuffers(); glEnableClientState(UNIFORM_BUFFER_UNIFIED_NV); glBufferAddressRangeNV (UBA, 0, addrView, viewSize); foreach (obj in scene) { ... // glBindBufferRange (UBO, 1, uboMatrices, obj.matrixOffset, maSize); glBufferAddressRangeNV(UBA, 1, addrMatrices + obj.matrixOffset, maSize); foreach ( batch in obj.primitive_group_material) { // glBindBufferRange (UBO, 2, uboMaterial, batch.materialOffset, mtlSize); glBufferAddressRangeNV(UBA, 2, addrMaterial + batch.materialOffset, mtlSize); ... } } Example On Using Bindless UBO New pointer for UBO#1 updated per Object New pointer for UBO#2 updated per Primitive group pointer for UBO#0 updated once for all objects regular UBO binds are now ignored!
  • 18.
    18 Siggraph Asia2014 Pointers must be aligned So do Ptr Offsets glGetIntegerv(GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT, &offsetAlignment); Normally: 256 bytes  gaps between each item Try to fit as much data as possible… Not the case if passing an index for array access (MDI + “Base-instance”) But requires special GLSL code (indexing) Bindless And Memory Alignement GPU Virtual Memory 64 bits address Uniform Material 0 Uniform Material 1 Uniform Material 2 … glBufferAddressRangeNV (UBA, 2, addrMaterial + batch.materialOffset , mtlSize); 256b Uniform array materials[] Material 0 Material 1 Material 2 … Uniform …
  • 19.
    19 Siggraph Asia2014 NV_command_list Key Concepts 1.Tokenized Rendering: some state changes and draw commands are encoded into binary data stream Depends on bindless technology 2.State Objects Whole OpenGL States (program, blending...) captured as an object Allows pre-validation of state combinations, later reuse of objects is very fast 3.Command List Object „Display-list“ paradigm but more flexible: buffer are outside (referenced by address), so content can still be modified (matrics, vertices...)
  • 20.
    20 Siggraph Asia2014 UpdateBuffers(); glBindBufferBase (UBO, 0, uboView); foreach (obj in scene) { // redundancy filter for these (if (used != last)... glBindVertexBuffer (0, obj.geometry->vbo, 0, vtxSize); glBindBuffer (ELEMENT, obj.geometry->ibo); glBindBufferRange (UBO, 1, uboMatrices, obj.matrixOffset, maSize); // iterate over cached material groups foreach ( batch in obj.materialGroups) { glBindBufferRange (UBO, 2, uboMaterial, batch.materialOffset, mtlSize); glMultiDrawElements (...); } } Typical Scene Drawing Example ~ 2 500 api drawcalls ~11 000 drawcalls ~55 triangles per call
  • 21.
    21 Siggraph Asia2014 UpdateBuffers(); glBindBufferBase (UBO, 0, uboView); foreach (obj in scene) { // redundancy filter for these (if (used != last)... glBindVertexBuffer (0, obj.geometry->vbo, 0, vtxSize); glBindBuffer (ELEMENT, obj.geometry->ibo); glBindBufferRange (UBO, 1, uboMatrices, obj.matrixOffset, maSize); // iterate over all parts individually foreach ( part in obj.parts) { if (part.material != lastMaterial){ glBindBufferRange (UBO, 2, uboMaterial, part.materialOffset, mtlSize); } glDrawElements (...); } } Typical Scene Drawing Example ~68 000 drawcalls ~10 triangles per call
  • 22.
    22 Siggraph Asia2014 Scene Drawing Converted To Token Buffer glDrawCommandsNV (GL_TRIANGLES, tokenBuffer , offsets[], sizes[], count); // {0}, {bufferSize}, 1 foreach (obj in scene) { glBufferAddressRangeNV(VERTEX.., 0, obj.geometry->addrVBO, ...); glBufferAddressRangeNV(ELEMENT..., 0, obj.geometry->addrIBO, ...); glBufferAddressRangeNV(UNIFORM..., 1, addrMatrices ...); foreach ( batch in obj.materialGroups) { glBufferAddressRangeNV(UNIFORM, 2, addrMaterial ...); glMultiDrawElements(...) } } becomes a single drawcall replaces 80k calls to GL (for graphic-card model) Token buffer Set Attr#0 on VBO address … Set Attr#1 on VBO address … Set Elements on EBO address … Uniform Matrix on UBO address … Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Obj#1 Obj#2 … For all objects …
  • 23.
    23 Siggraph Asia2014 Tokens-buffers are tightly packed structs in linear memory Token Buffer Structures TokenUbo { GLuint header; UniformAddressCommandNV { GLushort index; GLushort stage; GLuint64 address; } cmd; } TokenVbo { GLuint header; AttributeAddressCommandNV { GLuint index; GLuint64 address; } cmd; } TokenIbo { GLuint header; ElementAddressCommandNV { GLuint64 address; GLuint typeSizeInByte; } cmd; } TokenDrawElements { Gluint header; DrawElementsCommandNV { GLuint count; GLuint firstIndex; GLuint baseVertex; } cmd; } Token buffer Set Attr#0 on VBO address … Set Attr#1 on VBO address … Set Elements on EBO address … Uniform Matrix on UBO address … Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements … Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements Uniform Material on UBO address … DrawElements
  • 24.
    24 Siggraph Asia2014 Tokenized Rendering Token Headers are GPU commands, followed by arguments FRONTFACE_COMMAND_NV BLEND_COLOR_COMMAND_NV STENCIL_REF_COMMAND_NV LINE_WIDTH_COMMAND_NV POLYGON_OFFSET_COMMAND_NV ALPHA_REF_COMMAND_NV VIEWPORT_COMMAND_NV SCISSOR_COMMAND_NV ELEMENT_ADDRESS_COMMAND_NV ATTRIBUTE_ADDRESS_COMMAND_NV UNIFORM_ADDRESS_COMMAND_NV DRAW_ELEMENTS_COMMAND_NV DRAW_ARRAYS_COMMAND_NV DRAW_ELEMENTS_STRIP_COMMAND_NV DRAW_ARRAYS_STRIP_COMMAND_NV DRAW_ELEMENTS_INSTANCED_COMMAND_NV DRAW_ARRAYS_INSTANCED_COMMAND_NV TERMINATE_SEQUENCE_COMMAND_NV NOP_COMMAND_NV Final list might change Render States Index Buffer; Position Attribute; Normals; Texcoords... Matrices; Material data... Draw Commands ! Special Commands (see later)
  • 25.
    25 Siggraph Asia2014 Tokenized Rendering Example: UBO Address assignment structure FRONTFACE_COMMAND_NV BLEND_COLOR_COMMAND_NV STENCIL_REF_COMMAND_NV LINE_WIDTH_COMMAND_NV POLYGON_OFFSET_COMMAND_NV ALPHA_REF_COMMAND_NV VIEWPORT_COMMAND_NV SCISSOR_COMMAND_NV ELEMENT_ADDRESS_COMMAND_NV ATTRIBUTE_ADDRESS_COMMAND_NV UNIFORM_ADDRESS_COMMAND_NV DRAW_ELEMENTS_COMMAND_NV DRAW_ARRAYS_COMMAND_NV DRAW_ELEMENTS_STRIP_COMMAND_NV DRAW_ARRAYS_STRIP_COMMAND_NV DRAW_ELEMENTS_INSTANCED_COMMAND_NV DRAW_ARRAYS_INSTANCED_COMMAND_NV TERMINATE_SEQUENCE_COMMAND_NV NOP_COMMAND_NV TokenUbo { GLuint header; UniformAddressCommandNV { GLushort index; GLushort stage; GLuint64 address; } cmd; } Example Real Token to be queried header = glGetCommandHeaderNV( UNIFORM_ADDRESS_COMMAND_NV, Sizeof(TokenUbo) ) One Shading stage to target (not ‘program’) Stage = glGetStageIndexNV(S) (S: STAGE_VERTEX|GEOMETRY|FRAGMENT|TESS_CONTROL/EVAL) Hardware Index *not* Uniform Program index
  • 26.
    26 Siggraph Asia2014 TOKENIZED RENDERING Allows rendering of a mix of LIST, STRIP, FAN, LOOP modes in one go Pass „basic type“ as Token, use „mode“ for more in "Instanced" drawing TokenDrawElements { Gluint header; DrawElementsCommandNV { GLuint count; GLuint firstIndex; GLuint baseVertex; } cmd; } TokenDrawElementsInstanced { Gluint header; DrawElementsInstancedCommandNV { GLuint mode; GLuint count; GLuint instanceCount; GLuint firstIndex; GLuint baseVertex; GLuint baseInstance; } cmd; } LIST, STRIP, FAN, LOOP types (GL_LINE_LOOP...) DRAW_ELEMENTS_COMMAND_NV DRAW_ARRAYS_COMMAND_NV DRAW_ELEMENTS_STRIP_COMMAND_NV DRAW_ARRAYS_STRIP_COMMAND_NV glGetCommandHeaderNV() DRAW_ELEMENTS_INSTANCED_COMMAND_NV DRAW_ARRAYS_INSTANCED_COMMAND_NV glGetCommandHeaderNV()
  • 27.
    27 Siggraph Asia2014 TERMINATE_SEQUENCE: Occlusion Culling Now overcomes deficit of previous methods http://on-demand.gputechconf.com/gtc/2014/presentations/S4379-opengl-44-scene-rendering- techniques.pdf Enqueue all tokens for entire object Shader to Check Visibility; Shader for SCAN operation; Add TERMINATE_SEQUENCE_COMMAND_NV to end Technique Draw time GROUPED Timing GPU (ms) CPU (ms) 6.3 2.6 x 0.9 6 x CULL Old Bindless MDI (*) CULL NEW TOKEN native 0.2 27 x glBindBufferRange + drawcalls 16.8 5.4 6.2 2.7 x 6.3 0.85 x CULL Old Readback (stalls pipe) (*) K5000, Preliminary results, (*) taken from slightly differnt framework HW TOKEN-buffers ~0 BIG x No instancing! (synthetic test, data replication) SCENE: materials: 138 objects: 13,032 geometries: 3,312 parts: 789,464 triangles: 29,527,840 vertices: 27,584,376 16.8 5.3 3.1 x
  • 28.
    28 Siggraph Asia2014 Just a little... “commandBindableNV” turns binding IDs to Hardware IDs Texturing must go through bindless ARB_bindless_texture Regular Texture binding Turned Off Changing UBO Ptr Addresses == texture changes (here ‘myBuf’) Does Shaders Need Special Code ? #extension GL_ARB_bindless_texture : require #extension GL_NV_command_list : enable #if GL_NV_command_list layout(commandBindableNV) uniform; #endif layout(std140,binding=2) uniform myBuf { sampler2D mySampler; //or: in int whichSampler; }; layout(std140,binding=1) uniform samplers { sampler2D allSamplers[NUM_TEXTURES]; }; … c = texture(mySampler, tc); //or c = texture(allSamplers [ whichSampler ] , tc); … Example:
  • 29.
    29 Siggraph Asia2014 State Objects StateObject Encapsulates majority of state (fbo format, active shader, blend, depth ...) State Object immutable: gives more control over validation cost no bindings captured: bindless used instead; textures passed via UBO Primitive type is a state: participates to important validation work Cannot be put in the token buffer glCaptureStateNV(stateobject, GL_TRIANGLES ); Primitive type as argument: because it is part of states
  • 30.
    30 Siggraph Asia2014 Render entire scenes with different shaders/fbos... in one go Driver caches state transitions ! Draw With State Objects glDrawCommandsStatesNV( tokenBuffer, offsets[], sizes[], states[], fbos[], count); Token buffer VBO address … VBO address … EBO address … Uniform Matrix Uniform Material DrawElements Uniform Material DrawElements … EBO address … Uniform Matrix Uniform Material DrawElements Uniform Material DrawElements FBO 1 FBO 2 fbos[] FBO 1 FBO 1 State Obj 1 State Obj 2 State Obj 1 State Obj 4 Count = 4 States[] offsets[] sizes[0] sizes[1] sizes[2] sizes[3]
  • 31.
    31 Siggraph Asia2014 Driver bakes „Diff“ between states and apply only the difference Pseudo Code of glDrawCommandsStatesNV for i < count { if (i == 0) set state from states[i]; else set state transition states[i-1] to states[i] if (fbo[i]) { // fbo[i] must be compatible with states[i].fbo glBindFramebuffer( fbo[i] ) } else glBindFramebuffer( states[i].fbo ) ProcessCommandSequence(...tokenBuffer, offsets[i], sizes[i]) }
  • 32.
    32 Siggraph Asia2014 Rendering must always happen in a FBO Backbuffer Ptr. Address is un-reliable (dynamic re-alloc when resizing…) Use glBlitFramebuffer() for FBO  final Backbuffer result FBO Resources Must be Resident (glMakeTextureHandleResidentARB()) Resources can be replaced/swapped if they keep the same base configuration (attachment formats, # drawbuffers...) I.e. Same configuration as captured FBO settings from stateobject This is what happens when resizing: Detach & Destroy resource  create new ones  attach them to FBO(s) Frame-Buffer Objects And State Objects
  • 33.
    33 Siggraph Asia2014 Combine multiple token buffers & states into a CommandList object glCreateCommandListsNV(N, &list) glCommandListSegmentsNV(list, segs) Convenient for concatenation glListDrawCommandsStatesClientNV(list, segment, token-buffer-ptrs, token-buffer- sizes, states, FBOs, count) glCompileCommandListNV(list); glCallCommandListNV(list) Command-List Object System mem. VBO address … VBO address … EBO address … Uniform Matrix Uniform Material DrawElements … Uniform Material DrawElements FBO State Object System mem. VBO address … VBO address … EBO address … Uniform Matrix Uniform Material DrawElements … FBO State Object System mem. VBO address … VBO address … Uniform Matrix Uniform Material DrawArrays … Uniform Material DrawArrays FBO State Object … Command-List Segment #0 Segment #1
  • 34.
    34 Siggraph Asia2014 Command-List Object Less flexibilty compared to token buffer Token buffers taken from client pointers (CPU memory) Driver will optimize these token buffers and related state-objects Optimize State transitions; token cmds for the GPU Front-End Resulting command-list is immutable If any resource pointer changed, the command-list must be recompiled But still rather flexible possible to change content of referenced buffers! (matrices, materials, vertices...) Animation; skinning... No need for command-list recompilation
  • 35.
    35 Siggraph Asia2014 Command-List doesn’t pretend to solve any OpenGL multi-threading Multi-threading can help if complex CPU work going-on update of Vertex / Element buffers: transform. Matrices; skinning… Update of Token Buffers: adding/removing characters in a game scene… OpenGL & Multithreading issues: OpenGL is bad at sharing its access from various threads Make-Current or Multiple Contexts aren’t good solutions Prefer to keep context ownership to one main thread OpenGL And Multi-threading ?
  • 36.
    36 Siggraph Asia2014 Token Buffers and Vertex/Elements/Uniform Buffers (VBO/UBO) Token Buffer Objects; VBOs and UBOs owned by OpenGL Multi-threading can be used for data update if: Work on CPU system memory; then push data back to OpenGL (glBufferSubData) Or Request for a pointer (glMapBuffers); then work with it from the thread State Objects: State Object and their 'Capture' must be handled in OpenGL context No way to do it on a separate threads that don’t have OpenGL context Multi-threading And Command-List
  • 37.
    37 Siggraph Asia2014 Multi-threading Use-Case Example #1 Thread #0 OpenGL Ctxt Thread #1 Thread #1 Submit States PushAttrib() set states & and capture PopAttribs() Get State ID PushAttrib() set states & and capture PopAttribs() Submit States unmap Token buf. ask for Token buf. Ptr Build state list ask for Token buf. Ptr unmap Token buf. Build token cmds Get State ID Build token cmds Build token cmds ask for Token buf. Ptr unmap Token buf. ask for Token buf. Ptr ... ask for Token buf. Ptr Build token cmds unmap Token buf. Build token cmds Build state list
  • 38.
    38 Siggraph Asia2014 Multi-threading Use-Case Example #2 Split state capture from Token-buffer creation Thread 1 Thread 2 Thread 3 Build Token buffers in CPU memory Thread 0 OpenGL Ctxt Walk through whole scene and build State-Objects Receive Token-Buffers and issue them as Token Buffer Objects to OpenGL
  • 39.
    39 Siggraph Asia2014 Migration Steps All rendering via FBO (statecapture doesn‘t support default backbuffer) No legacy states in GLSL use custom uniforms no built-in uniforms (gl_ModelView...) use glVertexAttribPointer (no glTexCoordPointer etc.) No classic uniforms, pack them all in UBO ARB_bindless_texture for texturing Bindless Buffers ARB_vertex_attrib_binding combined with NV_vertex_buffer_unified_memory (VBUM)... Organize for StateObject reuse state capture expensive: Capture them at init. time; Factorize their use in the scene
  • 40.
    40 Siggraph Asia2014 Migration Tips Vertex Attributes and bindless VBO http://on-demand.gputechconf.com/siggraph/2014/presentation/SG4117- OpenGL-Scene-Rendering-Techniques.pdf (slide 11-16) GLSL // classic attributes ... normal = gl_Normal; gl_Position = gl_Vertex; // generic attributes // ideally share this definition across C and GLSL #define VERTEX_POS 0 #define VERTEX_NORMAL 1 in layout(location= VERTEX_POS) vec4 attr_Pos; in layout(location= VERTEX_NORMAL) vec3 attr_Normal; ... normal = attr_Normal; gl_Position = attr_Pos;
  • 41.
    41 Siggraph Asia2014 Migration Tips UBO Parameter management http://on-demand.gputechconf.com/siggraph/2014/presentation/SG4117- OpenGL-Scene-Rendering-Techniques.pdf ( 18-27, 44-47) Ideally group by frequency of change // classic uniforms uniform samplerCube viewEnvTex; uniform vec4 materialColor; uniform sampler2D materialTex; ... // UBO usage, bindless texture inside UBO, grouped by change layout(std140, binding=0, commandBindableNV) uniform view { samplerCube texViewEnv; }; layout(std140, binding=1, commandBindableNV) uniform material { vec4 materialColor; sampler2D texMaterialColor; }; ...
  • 42.
    42 Siggraph Asia2014 OpenGL Devtech 'Proviz' samples soon available on GitHub ! check https://github.com/nvpro-samples on a regular basis working on ramping-up https://developer.nvidia.com/samples & https://developer.nvidia.com/professional-graphics command-lists examples to come here this Dec. 2014 Many other samples will be pushed here as standalone repositories Beta Driver for Command-Lists: Release 346 for Dec.2014 Special Thanks to Pierre Boudier and Christoph Kubisch Questions/Feedback: tlorach@nvidia.com / ckubisch@nvidia.com Thanks!

Editor's Notes

  • #5 New APIs are meant to increase the efficiency of drivers by lowering their cost on CPU and thus shifting the workload over the GPU. This can translate to a better use of the GPU. But it can also translate to simply lowering the pressure over the CPU.