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cippyboy

DX11 Single vs Multiple Constant Buffers

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So basically after upgrading from DX9 to DX10 I read a lot of docs from Microsoft about how it's better to organize constant buffers by update frequency, so I made 3 types of constant buffers:

 

PerFrame (view & projection matrix)

PerMaterial (MaterialColor, specular, shinyness,etc)

PerObject ( world matrix )

 

I didn't really thought about performance considerations though but one day it stroke me, how about I just make 1 buffer to encapsulate all data ? So after I did this I noticed that performance actually increased by ~3-5%, even though I was updating an entire sightly bigger buffer. I thought that maybe drivers at the time (I was having a HD5770, a first gen DX11 device) are not that optimized for multiple constant buffers and reverted back to multiple buffers.

 

I now have a HD7850 and after doing this little test again, I'm seeing a performance boost of up to +50% for ~100 drawcalls when having a single huge constant buffer per object. So in effect, the difference is not smaller, it's bigger, signalling that there's something inherently wrong with having too many constant buffers binded. I'm now assuming this may be because my buffers are fairly small. The huge constant buffers is around 460 bytes ( I only have 4 matrices, one light and a few other variables ), so perhaps the multiple buffer switches are more advantageous when you are doing something like fetching an entire vertex buffer (for real-time ambient aocclusion based on vertices) or when you work with skinned meshes of 100 bones each.

 

My question is if you have tried to render a scene with multiple buffers and with a single huge buffer and compared performance ?

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I suspect that with the size of your constant buffers, that the cost to bind is actually greater than the cost to pass a small amount of data to the shader. How many objects are you rendering? how many objects per material? the frequency of updates on these constant buffers would have implications in regards to your performance. Even an object with 1 bone will contain 2x as many bytes as your current per object buffer. Try to increase the size of that per object buffer and see what happens to your performance data.

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There are around 107 objects and for the most part it's just 1-3 objects per material, so I have around 107 materials too. However, with the 3 constant buffers I was only updating the perframe buffer once per frame and then each material had it's own permaterial buffer and each object it's own perobject buffer that didn't change ( I don't animate any objects or material properties currently), so only the view/projection matrices changed.

 

Also, why do you say 1 bone would be 2x my current per object buffer ? 1 bone would be just a float4x4 so that's like 64 bytes. I'm planning to do some skinning in the near future and I have around 30 bones, so I'm curious how that will go.

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Do you know if the performance difference is on the CPU-side, GPU-side, or both?

How many ms per frame is your game using in both scenarios?

How are you creating/updating the buffers?

How are you applying these state changes?

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How can I tell if it's CPU or GPU since both techniques result in a 99% GPU usage ? (according to Catalyst control center)

3 CB result in ~400 FPS (or 2.5ms per frame), and 1 CB results in ~660 FPS ( or ~1.51 ms per frame). The CPU is not a bottleneck, even GPU Perf Client says this, CPU is doing ~0.27ms work per frame.

 

Creating them with usage default, and using UpdateSubResource. I was previously using Map/Unmap with write discard but there's just no performance difference between the two.

How am I applying state changes ? Through PSSetConstantBuffers :). I do admit I call PSSetConstantBuffers 3 times for 3 constant buffers instead of calling it once with all the 3 buffers, but I kind of doubt my speed penalty of ~50% is due to state changes.

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PSSetConstantBuffers 3 times per object or 3 times per frame?

The only difference in your D3D code between 1 and 3 constant buffers should be how many bytes you send to the constant buffer for each object, except for once-per-frame setup. If you draw 1000 objects with 1 constant buffer you do 1 Map and 1 Draw per object. If you draw 1000 objects with 2 constant buffers, you still do 1 Map and 1 Draw per object, it's just that you Map a constant buffer with fewer bytes since the camera matrices are in a once-per-frame setup constant buffer that doesn't change between objects, and so doesn't need to be touched. You should never set the constant buffers with *SetConstantBuffers more than once per frame. Even if you change shaders the constant buffers remain set and do not need a new call to *SetConstantBuffers.

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"each object it's own perobject buffer that didn't change"

 

This is definitely the cause of your observed performance differences.  With - say - 100 objects, you're making 100 SetConstantBiuffers calls, and they're more expensive than discarding and refilling a single buffer.

 

In the past, I've observed that the best performance comes from:

 

 - One per-frame buffer.

 - One per-material buffer, irrespective of how many materials you have.

 - One per-object buffer, irrespective of how many objects you have.

 

When changing materials you just Map with Discard, then write in the new material properties.  When drawing a new object you also Map with Discard and write in the new object properties.  This is substantially cheaper than having to switch buffers each time, and also lends itself well to piggybacking instancing on top of the same code when time comes to do that.

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This is definitely the cause of your observed performance differences.  With - say - 100 objects, you're making 100 SetConstantBiuffers calls, and they're more expensive than discarding and refilling a single buffer.

 

 

interesting, benchmarking my engine I found calling SetConstantBuffers with pre filled (ie. one per scene material) buffers faster than having one buffer mapped with Map for every material change.

From what I understand, a constant buffer exists in video memory, so calling SetConstantBuffer is just updating "a pointer to data" on the GPU while Map is actually moving data from the cpu.

 

At the end of the day, always benchmark (on different GPUs) before committing to a strategy.

Edited by kunos

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"each object it's own perobject buffer that didn't change"

 

This is definitely the cause of your observed performance differences.  With - say - 100 objects, you're making 100 SetConstantBiuffers calls, and they're more expensive than discarding and refilling a single buffer.

 

In the past, I've observed that the best performance comes from:

 

 - One per-frame buffer.

 - One per-material buffer, irrespective of how many materials you have.

 - One per-object buffer, irrespective of how many objects you have.

 

When changing materials you just Map with Discard, then write in the new material properties.  When drawing a new object you also Map with Discard and write in the new object properties.  This is substantially cheaper than having to switch buffers each time, and also lends itself well to piggybacking instancing on top of the same code when time comes to do that.

 

I tried that once, all materials having their own PerMaterial buffer versus having a single material buffer and constantly updating that but the performance difference was almost 0.

 

So basically one buffer update (the per frame buffer) and 300 buffer sets ( even though I set the same perframe buffer which should be a no-op ), is slower than 100 buffer updates and 100 buffer sets.

 

Have you tried just making one single buffer versus the 3 you're mapping/discarding on a per object basis ? That was my question all along, if someone tried one buffer versus multiple, I'm really curious about your results.

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Tried it right now, and got zero difference between them, even with abnormally large buffers, though in certain cases with one very large buffer and one very small and already a high usage of bandwidth to video memory for other things there can certainly be a difference...

 

Consider a case where a complex shader indexes into a constant buffer of a couple of thousand vectors that doesn't change between objects, and there's 1000 objects where the only change is the translation matrix, then uploading 64 bytes per object is much better than 32,000 bytes, especially if each frame there is also a couple of different transfers of reasonably large dynamic textures going on.

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if (FAILED(hr)) { return false; } //Load Constant Buffers D3D11_BUFFER_DESC cBufferDesc{}; cBufferDesc.ByteWidth = sizeof(XMMATRIX); cBufferDesc.Usage = D3D11_USAGE_DEFAULT; cBufferDesc.BindFlags = D3D11_BIND_CONSTANT_BUFFER; for (size_t bufferID = 0; bufferID < NumConstantBuffers; bufferID++) { hr = g_d3dDevice->CreateBuffer(&cBufferDesc, nullptr, &g_d3dConstantBuffers[bufferID]); if (FAILED(hr)) { return false; } } //Setup Projection Matrix RECT client{}; GetClientRect(g_WinHnd, &client); float clientWidth = static_cast<float>(client.right - client.left); float clientHeight = static_cast<float>(client.bottom - client.top); g_ProjectionMatrix = DirectX::XMMatrixPerspectiveFovLH(XMConvertToRadians(45.0f), clientWidth / clientHeight, 0.1f, 100.0f); g_d3dDeviceContext->UpdateSubresource(g_d3dConstantBuffers[CB_Application], 0, nullptr, &g_ProjectionMatrix, 0, 0); return true; } void Update(float deltaTime) { XMVECTOR eyePosition = XMVectorSet(0, 0, -10, 1); XMVECTOR focusPoint = XMVectorSet(0, 0, 0, 1); XMVECTOR upDirection = XMVectorSet(0, 1, 0, 0); g_ViewMatrix = DirectX::XMMatrixLookAtLH(eyePosition, focusPoint, upDirection); g_d3dDeviceContext->UpdateSubresource(g_d3dConstantBuffers[CB_Frame], 0, nullptr, &g_ViewMatrix, 0, 0); static float angle = 0.0f; angle += 90.0f * deltaTime; XMVECTOR rotationAxis = XMVectorSet(0, 1, 1, 0); g_WorldMatrix = DirectX::XMMatrixRotationAxis(rotationAxis, XMConvertToRadians(angle)); g_d3dDeviceContext->UpdateSubresource(g_d3dConstantBuffers[CB_Object], 0, nullptr, &g_WorldMatrix, 0, 0); } void Clear(const FLOAT clearColor[4], FLOAT clearDepth, UINT8 clearStencil) { g_d3dDeviceContext->ClearRenderTargetView(g_d3dRenderTargerView, clearColor); g_d3dDeviceContext->ClearDepthStencilView(g_d3dDepthStencilView, D3D11_CLEAR_DEPTH | D3D11_CLEAR_STENCIL, clearDepth, clearStencil); } void Present(bool vSync) { if (vSync) { g_d3dSwapChain->Present(1, 0); } else { g_d3dSwapChain->Present(0, 0); } } void Render() { assert(g_d3dDevice); assert(g_d3dDeviceContext); Clear(Colors::CornflowerBlue, 1.0f, 0); //IA const UINT vertexStride = sizeof(VertexPosColor); const UINT offset = 0; g_d3dDeviceContext->IASetVertexBuffers(0, 1, &g_d3dVertexBuffer, &vertexStride, &offset); g_d3dDeviceContext->IASetInputLayout(g_d3dInputLayout); g_d3dDeviceContext->IASetIndexBuffer(g_d3dIndexBuffer, DXGI_FORMAT_R16_UINT, 0); g_d3dDeviceContext->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST); //VS g_d3dDeviceContext->VSSetShader(g_d3dVertexShader, nullptr, 0); g_d3dDeviceContext->VSGetConstantBuffers(0, NumConstantBuffers, g_d3dConstantBuffers); //RS g_d3dDeviceContext->RSSetState(g_d3dRasterizerState); g_d3dDeviceContext->RSSetViewports(1, &g_Viewport); //PS g_d3dDeviceContext->PSSetShader(g_d3dPixelShader, nullptr, 0); //OM g_d3dDeviceContext->OMSetRenderTargets(1, &g_d3dRenderTargerView, g_d3dDepthStencilView); g_d3dDeviceContext->OMSetDepthStencilState(g_d3dDepthStencilState, 1); //draw g_d3dDeviceContext->DrawIndexed(_countof(g_Indicies), 0, 0); Present(g_EnableVSync); } void CleanUp() { SafeRelease(g_d3dVertexShader); SafeRelease(g_d3dPixelShader); SafeRelease(g_d3dVertexBuffer); SafeRelease(g_d3dIndexBuffer); SafeRelease(g_d3dInputLayout); SafeRelease(g_d3dDepthStencilBuffer); for (size_t bufferID = 0; bufferID < NumConstantBuffers; bufferID++) { SafeRelease(g_d3dConstantBuffers[bufferID]); } SafeRelease(g_d3dDepthStencilState); SafeRelease(g_d3dRasterizerState); SafeRelease(g_d3dRenderTargerView); SafeRelease(g_d3dDepthStencilView); SafeRelease(g_d3dSwapChain); SafeRelease(g_d3dDeviceContext); SafeRelease(g_d3dDevice); }  
    • By MarcusAseth
      Hi guys, I'm trying to learn this stuff but running into some problems 😕
      I've compiled my .hlsl into a header file which contains the global variable with the precompiled shader data:
      //... // Approximately 83 instruction slots used #endif const BYTE g_vs[] = { 68, 88, 66, 67, 143, 82, 13, 236, 152, 133, 219, 113, 173, 135, 18, 87, 122, 208, 124, 76, 1, 0, 0, 0, 16, 76, 0, 0, 6, 0, //.... And now following the "Compiling at build time to header files" example at this msdn link , I've included the header files in my main.cpp and I'm trying to create the vertex shader like this:
      hr = g_d3dDevice->CreateVertexShader(g_vs, sizeof(g_vs), nullptr, &g_d3dVertexShader); if (FAILED(hr)) { return -1; } and this is failing, entering the if and returing -1.
      Can someone point out what I'm doing wrong? 😕 
    • By Toastmastern
      Hello everyone,
      After a few years of break from coding and my planet render game I'm giving it a go again from a different angle. What I'm struggling with now is that I have created a Frustum that works fine for now atleast, it does what it's supose to do alltho not perfect. But with the frustum came very low FPS, since what I'm doing right now just to see if the Frustum worked is to recreate the vertex buffer every frame that the camera detected movement. This is of course very costly and not the way to do it. Thats why I'm now trying to learn how to create a dynamic vertexbuffer instead and to map and unmap the vertexes, in the end my goal is to update only part of the vertexbuffer that is needed, but one step at a time ^^

      So below is my code which I use to create the Dynamic buffer. The issue is that I want the size of the vertex buffer to be big enough to handle bigger vertex buffers then just mPlanetMesh.vertices.size() due to more vertices being added later when I start to do LOD and stuff, the first render isn't the biggest one I will need.
      vertexBufferDesc.Usage = D3D11_USAGE_DYNAMIC; vertexBufferDesc.ByteWidth = mPlanetMesh.vertices.size(); vertexBufferDesc.BindFlags = D3D11_BIND_VERTEX_BUFFER; vertexBufferDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE; vertexBufferDesc.MiscFlags = 0; vertexBufferDesc.StructureByteStride = 0; vertexData.pSysMem = &mPlanetMesh.vertices[0]; vertexData.SysMemPitch = 0; vertexData.SysMemSlicePitch = 0; result = device->CreateBuffer(&vertexBufferDesc, &vertexData, &mVertexBuffer); if (FAILED(result)) { return false; } What happens is that the 
      result = device->CreateBuffer(&vertexBufferDesc, &vertexData, &mVertexBuffer); Makes it crash due to Access Violation. When I put the vertices.size() in it works without issues, but when I try to set it to like vertices.size() * 2 it crashes.
      I googled my eyes dry tonight but doesn't seem to find people with the same kind of issue, I've read that the vertex buffer can be bigger if needed. What I'm I doing wrong here?
       
      Best Regards and Thanks in advance
      Toastmastern
    • By yonisi
      Hi,
      I have a terrain engine where the terrain and water are on different grids. So I'm trying to render planar reflections of the terrain into the water grid. After reading some web pages and docs and also trying to learn from the RasterTek reflections demo and the small water bodies demo as well. What I do is as follows:
      1. Create a Reflection view matrix  - Technically I ONLY flip the camera position in the Y direction (Positive Y is up) and add to it 2 * waterLevel. Then I update the View matrix and I save that matrix for later. The code:
      void Camera::UpdateReflectionViewMatrix( float waterLevel ) { mBackupPosition = mPosition; mBackupLook = mLook; mPosition.y = -mPosition.y + 2.0f * waterLevel; //mLook.y = -mLook.y + 2.0f * waterLevel; UpdateViewMatrix(); mReflectionView = View(); } 2. I render the Terrain geometry to a 512x512 sized Render target by using the Reflection view matrix and an opposite culling (My Terrain is using front culling by nature so I'm using back culling for the Reflction render pass). Let me say that I checked with the Graphics debugger and the Reflection Render target looks "OK" at this stage (Picture attached). I don't know if the fact that the terrain is shown only at the top are of the texture is expected or not, but it seems OK.

      3. Render the Reflection texture into the water using projective texturing - I hope this step is OK code wise. Basically I'm sending to the shader the WorldReflectionViewProj matrix that was created at step 1 in order to use it for the projective texture coordinates, I then convert the position in the DS (Water and terrain are drawn with Tessellation) to the projective tex coords using that WorldReflectionViewProj matrix, then I sample the reflection texture after setting up the coordinates in the PS. Here is the code:
      //Send the ReflectionWorldViewProj matrix to the shader: XMStoreFloat4x4(&mPerFrameCB.Data.ReflectionWorldViewProj, XMMatrixTranspose( ( mWorld * pCam->GetReflectedView() ) * mProj )); //Setting up the Projective tex coords in the DS: Output.projTexPosition = mul(float4(worldPos.xyz, 1), g_ReflectionWorldViewProj); //Setting up the coords in the PS and sampling the reflection texture: float2 projTexCoords; projTexCoords.x = input.projTexPosition.x / input.projTexPosition.w / 2.0 + 0.5; projTexCoords.y = -input.projTexPosition.y / input.projTexPosition.w / 2.0 + 0.5; projTexCoords += normal.xz * 0.025; float4 reflectionColor = gReflectionMap.SampleLevel(SamplerClampLinear, projTexCoords, 0); texColor += reflectionColor * 0.25; I'll add that when compiling the PS I'm getting a warning on those dividing by input.projTexPosition.w for a possible float division by 0, I tried to add some offset or some minimum to the dividing term but that still not solved my issue.
      Here is the problem itself. At relatively flat view angles I'm seeing correct reflections (Or at least so it seems), but as I pitch the camera down, I'm seeing those artifacts which I have no idea where are coming from. I'm culling the terrain in the reflection render pass when it's lower than water height (I have heightmaps for that).
       
      Any help will be appreciated because I don't know what is wrong or where else to look.
    • By thmfrnk
      Hi,
      I am looking for a usefull commandline based texture compression tool with the rights to be able to ship with my application. It should have following caps:
      Supports all major image format as source files (jpeg, png, tga, bmp) Export as DDS Compression Formats BC1, BC2, BC3, BC4, BC7 I am actually using the nvdxt tool from Nvidia, but it does not support BC4 (which I need for one-channel 8bit textures). Everything else which I found wasn't really useful.
      Any suggestions?
      Thx
       
    • By trojanfoe
      I have been trying to create a BlendState for my UI text sprites so that they are both alpha-blended (so you can see them) and invert the pixel they are rendered over (again, so you can see them).
      In order to get alpha blending you would need:
      SrcBlend = SRC_ALPHA DestBlend = INV_SRC_ALPHA and in order to have inverted colours you would need something like:
      SrcBlend = INV_DEST_COLOR DestBlend = INV_SRC_COLOR and you can't have both.
      So I have come to the conclusion that it's not possible; am I right?
    • By Royma
      In traditional way, it needs 6 passes for a point light and many passes for cascaded shadow mapping to generate shadow maps. Recently I learnt a method that using a geometry shader to generate all the shadow maps in one pass.I specify a render target and a depth-stencil buffer which are both Texture2dArray in DirectX11.It looks much better than the traditional way I think.But after I implemented it, I found cascaded shadow mapping runs much slower than the traditional way.The fps slow down from 60 to 35.I don't know why.I guess may be I should do some culling or maybe the geometry shader is not efficient.
      I want to know the reason that I reduced the drawcalls from 8 to 1, but it runs slow down.Should I abandon this method or is there any way to optimize this method to run more efficiently than multi-pass rendering?
      Here is the gs code:

      [maxvertexcount(24)]
      void main(
          triangle DepthGsIn input[3] : SV_POSITION,
          inout TriangleStream< DepthPsIn > output
      )
      {
          for (uint k = 0; k < 8; ++k)
          {
              DepthPsIn element;
              element.RTIndex = k;
              for (uint i = 0; i < 3; ++i)
              {
                  float2 shadowSlopeBias = calculateShadowSlopeBias(input.normal, -g_cameras[k].world[1]);
                  float shadowBias = shadowSlopeBias.y * g_cameras[k].shadowMapParameters.x + g_cameras[k].shadowMapParameters.y;
                  element.position = input.position + shadowBias * g_cameras[k].world[1];
                  element.position = mul(element.position, g_cameras[k].viewProjection);
                  element.depth = element.position.z / element.position.w;
                  
                  output.Append(element);
              }
              output.RestartStrip();
          }
      }
       
    • By savail
      Hey,
      There are a few things which confuse me regarding DirectX 11 and HLSL shaders in general. I would be very grateful for your advice!
      1. Let's take for example a scene which invokes 2 totally separate pipeline render passes interchangeably. I understand I need to bind correct shaders for each of the render pass and potentially blend/depth or rasterizer state but what about resources such as Constant Buffers, Shader Resource Views and Unordered Access Views? Assuming that the second render pass uses none of the resources used by the first pass, do I still need to unbind the resources and clean pipeline state after first pass? Or is it ok to leave pipeline with unbound garbage since anything I'd need to bind for second pass would overwrite contents in the appropriate register slots anyway?
      2. Is it a good practice to assign register slots manually to all resources in HLSL?
      3. I thought about assigning manually register slots for every distinct render pass up to the maximum slot limit if neccessary. For example in 1 render pass I invoke 3 CS's, 2 VS's and 2 PS's and for all resources used by those shaders I try to fill as many register slots as neccessary and potentially reuse many times the same slot in shaders sharing the same resource. I was wondering if there is any performance penalty or gain when I bind all of my needed resources at the start of render pass and never gonna have to do it again until next render pass? - this means potentially binding a lot of registers and having excessive number of bound resources for every shader that is run.
      4. Is it a good practice to create a separate include file for every resource that occurs in >= 2 shader files or is it better to duplicate the declarations? In first case, the code is imo easier to maintain and edit but might be harder to read if there's too many includes. I've come up with a compromise between these 2 like this: create a separate include file for every CB that occurs in >= 2 shader files and a separate include file for every sampler I ever need to use. All other resources like srvs and uavs I prefer to duplicate in multiple shaders because they take much less space than CB for example... I'm not sure however if that's a good practice
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