Cuda Timeout when using KdTree Accelerators

Gaming and Visualization Technologies Visualization OptiX
1

Hi to all of you,

I use OptiX for an ordinary raytracer. Until now i could fix every problem by myself or using google.
I load a scenegraph and build an OptiX-Context accordingly:
At the root I use a RTGroup and an attached BVH-Accelerator.
Below this root is an arbitrary Tree of RTGroups (nodes), each with an attached BVH-Accelerator.
At the leafs I use RTGeometrygroups, again each with an attached BVH-Accelerator and a RTGeometry.
This system works, i get the desired frames.

Since all the geometry consists of triangles I want to use the accelerators for triangles (TriangleKdTree/KdTree) at the lowest level (RTGeometrygroup). Therefore this is the only thing i changed from the working system.
I set the vertex and index buffers as follows:

rtAccelerationCreate(m_context, &m_o_accel);
rtAccelerationSetBuilder(m_o_accel, "TriangleKdTree");
rtAccelerationSetTraverser(m_o_accel, "KdTree");
rtAccelerationSetProperty(m_o_accel, "vertex_buffer_name", "vertexBuffer");
rtAccelerationSetProperty(m_o_accel, "vertex_buffer_stride", "0");
rtAccelerationSetProperty(m_o_accel, "index_buffer_name", "vertexIndexBuffer");
rtAccelerationSetProperty(m_o_accel, "index_buffer_stride", "0");

But I get the following error:

Unknown error (Details: Function "RTresult _rtContextLaunch2D(RTcontext_api*,
 unsigned int, RTsize, RTsize)" caught exception: Encountered a CUDA error: 
Kernel launch returned (702): Launch timeout, [6619200])

If I am not mistaken, this means that the call to rtContextLaunch2D takes too long.
Therefore I tried to minimize the work:

  • 6x6 Pixel
  • no recursion but to the lightsources --> no shadows, transparencies, refractions, reflections
  • 589 vertices in 5 buffers
  • 3348 vertex indices in 5 buffers
  • before first real launch a call to rtContextLaunch2D(context, 0, 0) --> compiles in 5.5-6.5s

The system is as follows:

  • SUSE Linux Enterprise Desktop 11 (x86_64)
  • Quadro 6000
  • Nvidia driver 304.54
  • Cuda 5.0
  • OptiX 3.0.1

I tried manipulating the buffers length and names, getting validation error, to assure that they are correct. Those are the same buffers I use in the intersection test:

RT_PROGRAM void mesh_intersect(int primIdx){
   int v_id0 = vertexIndexBuffer[primIdx * 3 + 0];
   int v_id1 = vertexIndexBuffer[primIdx * 3 + 1];
   int v_id2 = vertexIndexBuffer[primIdx * 3 + 2];

   float3 p0 = vertexBuffer[v_id0];
   float3 p1 = vertexBuffer[v_id1];
   float3 p2 = vertexBuffer[v_id2];

   //intersections tests follow
}

Is it even possible to mix the different acceleration structures for the different tiers of the tree?

I hope someone can point me in the right direction to fix this problem!

If you need further information I will gladly provide it (hopefully not a smallest working example, which would be rather hard to make because the application uses MPI to work on a distributed system)

Greetings
Frieder

2

If you’re experiencing a timeout, the first and easiest thing to do is implement a callback function. This will return control to the CPU every so often to avoid the CPU thinking that the GPU is unresponsive. See the documentation for rtContextSetTimeoutCallback.

3

Thank you for the reply:)

I will try that, but i do not think it will solve the problem.
Since i reduced the workload to almost nothing (if you compare it to what OptiX can compute), and it still needs so long, the problems appears to be somewhere else.

4

How about upgrading to the latest versions of OptiX (3.6) and CUDA (6.0)?
I prefer Sbvh over KdTree, you might try that as well.

5

I implemented the callback function. It gets called while compiling (which was expected), but not during the normal context launch. The error remains.

Sbvh works fine. If i understand the programming guide correctly, this accelerated can use the triangle buffers as well (which is still set). So i am confused that it works with Sbvh but not the KdTree.

Updating is not an option right now, the GPU-Cluster i work on is not administrated by myself.