Warning Num Samples Per Thread Reduced To 32768 Rendering Might Be Slower [verified] May 2026

The warning "Num samples per thread reduced to 32768, rendering might be slower" is a common diagnostic message in V-Ray GPU (and occasionally other CUDA-based renderers like Octane). While it sounds alarming, it primarily indicates that your scene is pushing the limits of your GPU's Video RAM (VRAM). What the Warning Means

Target Resolutions: High-resolution renders (like 4K) require larger internal buffers, which consume more VRAM and can trigger the reduction.  How to Fix It  The warning "Num samples per thread reduced to

1. Adjust rendering settings: Reduce the resolution, decrease the number of samples, or adjust other rendering settings to alleviate the load on the rendering engine.
2. Increase system resources: Upgrade system hardware, such as adding more RAM or CPU cores, to provide the rendering engine with more resources to handle complex scenes.
3. Optimize scenes: Simplify complex scenes by reducing polygon counts, using more efficient shaders, or optimizing texture usage.
4. Update rendering software: Ensure that the rendering software or engine is up-to-date, as newer versions may include performance optimizations or improved handling of complex scenes.

5. How to Fix or Mitigate the Warning

You cannot always eliminate the warning entirely, but you can reduce its performance impact or adjust settings to avoid triggering it. Adjust rendering settings : Reduce the resolution, decrease

Large Textures: 4K or higher textures can quickly fill VRAM. decrease the number of samples

C. Driver or API Enforced Limits

• OpenCL, CUDA, or Metal backends may impose a maximum work‑group size or per‑thread buffer limit (e.g., 32KB, 64KB).
• When your requested samples exceed this, the driver truncates the value to the nearest safe limit (often 32768).