Hello,

I want to improve the performance of my game (engine) and some of your helped me to make a GPU Profiler. After creating the GPU Profiler, I started to measure the time my GPU needs per frame. I refined my GPU time measurements to find my bottleneck.

Searching the bottleneck

Rendering a small scene in an Idle state takes around 15.38 ms per frame. 13.54 ms (88.04%) are spent while rendering the scene, 1.57 ms (10.22%) are spent during the SwapChain.Present call (no VSync!) and the rest is spent on other tasks like rendering the UI. I further investigated the scene rendering, since it takes über 88% of my GPU frame rendering time.

When rendering my scene, most of the time (80.97%) is spent rendering my models. The rest is spent to render the background/skybox, updating animation data, updating pixel shader constant buffer, etc. It wasn't really suprising that most of the time is spent for my models, so I further refined my measurements to find the actual bottleneck.

In my example scene, I have five animated NPCs. When rendering these NPCs, most actions are almost for free. Setting the proper shaders in the input layout (0.11%), updating vertex shader constant buffers (0.32%), setting textures (0.24%) and setting vertex and index buffers (0.28%). However, the rest of the GPU time (99.05% !!) is spent in two function calls: DrawIndexed and DrawIndexedInstance.

I searched this forum and the web for other articles and threads about these functions, but I haven't found a lot of useful information. I use SharpDX and .NET Framework 4.5 to develop my game (engine). The developer of SharpDX said, that "The method DrawIndexed in SharpDX is a direct call to DirectX" (Source). DirectX 11 is widely used and SharpDX is "only" a wrapper for DirectX functions, I assume the problem is in my code.

How I render my scene

When rendering my scene, I render one model after another. Each model has one or more parts and one or more positions. For example, a human model has parts like head, hands, legs, torso, etc. and may be placed in different locations (on the couch, on a street, ...). For static elements like furniture, houses, etc. I use instancing, because the positions never change at run-time. Dynamic models like humans and monster don't use instancing, because positions change over time.

When rendering a model, I use this work-flow:

1. Set vertex and pixel shaders, if they need to be updated (e.g. PBR shaders, simple shader, depth info shaders, ...)
2. Set animation data as constant buffer in the vertex shader, if the model is animated
3. Set generic vertex shader constant buffer (world matrix, etc.)
4. Render all parts of the model. For each part:
   1. Set diffuse, normal, specular and emissive texture shader views
   2. Set vertex buffer
   3. Set index buffer
   4. Call DrawIndexedInstanced for instanced models and DrawIndexed models

What's the problem

After my GPU profiling, I know that over 99% of the rendering time for a single model is spent in the DrawIndexedInstanced and DrawIndexed function calls. But why do they take so long? Do I have to try to optimize my vertex or pixel shaders? I do not use other types of shaders at the moment. "Le Comte du Merde-fou" suggested in this post to merge regions of vertices to larger vertex buffers to reduce the number of Draw calls. While this makes sense to me, it does not explain why rendering my five (!) animated models takes that much GPU time. To make sure I don't analyse something I wrong, I made sure to not use the D3D11_CREATE_DEVICE_DEBUG flag and to run as Release version in Visual Studio as suggested by Hodgman in this forum thread.

My engine does its job. Multi-texturing, animation, soft shadowing, instancing, etc. are all implemented, but I need to reduce the GPU load for performance reasons. Each frame takes less than 3ms CPU time by the way. So the problem is on the GPU side, I believe.

One of the NPC models has 3,339 vertices. The other NPC models will have a similar amount of vertices.

I am running my tests on a Laptop with a GeForce GTX 1050 Ti and Intel(R) HD Graphics 630.

At the moment, I do not use any type of post-processing. My engine can handle topics like Soft Shadowing, but they are all disabled at the moment (because of performance problems on older computers).

How many draw calls do you make per frame?

I am sorry for my late response, but I was out of office. I did not have the time to read the presentations you linked, but I will read them this weekend. I could solve my performance issue. In my game engine, I check all installed graphics adapter and I use the one with the highest memory and the highest possible Feature Level. As it turned out, my testing laptop gave the same result for all graphics adapter although an Intel HD 630 chip is clearly weaker than my GeForce GTX 1050 Ti chip. I adjusted the system settings and now everything runs smooth.

VSync was turned off. In my main menu, I had around 2 ms per frame, because no 3D models were rendered. When I used a more complex scene in my game, the GPU needed 80 ms per frame. Therefore, I had lag. Using the correct graphics chips, the GPU was reduced by a factor of 10 to around 1 ms per frame in my default case and around 10 ms in very complex scenes.

I will update my FAQ, so all players know about this issue.