Understanding Texture Memory and Its Enabling Effect on L1/Texture Cache in CUDA 10.2 for Jetson Nano (Maxwell Architecture)
In computer graphics, texture memory is a high-level hardware cache used to store texture maps, which are 2D images used to add detail and color to 3D models. Texture memory is essential for efficient rendering, as it allows for quick access to texture data during model rendering. This article focuses on texture memory and its enabling effect on L1/Texture Cache in CUDA 10.2 for Jetson Nano, which uses the Maxwell architecture.
Bilinear Interpolation vs. Global Memory
When it comes to texture mapping, there are two primary methods for accessing texture data: bilinear interpolation and global memory. Bilinear interpolation is a technique for finding the color of a pixel in a texture map that lies between four known colors. Global memory, on the other hand, is the main memory available on a GPU, and it is slower than texture memory due to the longer access times.
A simple bilinear interpolation kernel implemented using global memory may look like the following:
__global__ void bilinearInterpolationKernel(float4 *texture, float x, float y, float4 &color)
{
int u = __float2int(x);
int v = __float2int(y);
float dx = x - u;
float dy = y - v;
float4 topLeft = texture[v * WIDTH + u];
float4 topRight = texture[(v + 1) * WIDTH + u];
float4 bottomLeft = texture[v * WIDTH + u + 1];
float4 bottomRight = texture[(v + 1) * WIDTH + u + 1];
color = topLeft * (1.0f - dx) * (1.0f - dy) + topRight * dx * (1.0f - dy) + bottomLeft * (1.0f - dx) * dy + bottomRight * dx * dy;
}
In this code, the kernel takes a texture pointer, the texture coordinates, and a float4 variable to store the resulting color. It calculates the integer texture coordinates and the fractional parts, then uses those to interpolate the four surrounding texels. This method, while functional, can be slow due to the use of global memory for texture access.
Texture Memory and its Enabling Effect on L1/Texture Cache
Texture memory is stored in a dedicated cache on the GPU, separate from global memory. This cache is optimized for texture mapping, providing faster access to texture data during rendering. Texture memory can be accessed through texture objects, which can be configured to use various filtering modes, such as bilinear interpolation. This is done using the CUDA runtime API.
Using texture memory can significantly improve performance, as it reduces the number of global memory accesses required for texture mapping. In addition, texture memory can enable the use of the L1/Texture cache, which is a high-speed cache on the Jetson Nano that is optimized for texture data. The L1/Texture cache can further improve performance by reducing the number of cache misses and increasing the hit rate of texture accesses.
To use texture memory in CUDA, you need to create a texture object using the CUDA runtime API. The following code shows how to create a texture object using bilinear interpolation filtering mode:
texture texObj;
cudaChannelFormatDesc channelDesc = cudaCreateChannelDesc
```less
;
cudaMemcpyToArray(texArray, 0, 0, dev_texture, size * sizeof(float4), cudaMemcpyHostToDevice);
texObj.addressMode[0] = cudaAddressModeClamp;
texObj.addressMode[1] = cudaAddressModeClamp;
texObj.filterMode = cudaFilterModeLinear;
texObj.normalized = false;
cudaBindTextureToArray(texObj, texArray, channelDesc);
```
In this code, a texture object (texObj) is created with a 2D texture reference and cudaReadModeElementType. The texture is also bound to a texture array (texArray) to allow for texture mapping. The filter mode is set to cudaFilterModeLinear, which enables bilinear interpolation for texture access.
- Texture memory is a high-level cache used for texture mapping and is stored separately from global memory. It provides faster access to texture data and can be accessed through texture objects, which can be configured to use various filtering modes.
- Bilinear interpolation is a technique for finding the color of a pixel in a texture map that lies between four known colors. While it can be implemented using global memory, it is slower than using texture memory due to longer access times.
- The L1/Texture cache is a high-speed cache on the Jetson Nano that is optimized for texture data. Enabling texture memory can enable the use of the L1/Texture cache, which can further improve performance.
References
- NVIDIA. (2021). CUDA Toolkit Documentation: Texture Objects. https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#texture-objects
- NVIDIA. (2021). Jetson Nano Developer Guide: L1 Cache. https