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| 1 | +/* |
| 2 | +Kernels to demonstrate permute operation. |
| 3 | +
|
| 4 | +Compile example: |
| 5 | +nvcc -O3 permute.cu -o permute |
| 6 | +
|
| 7 | +The goal is to permute a 4D matrix from its original shape (dim1, dim2, dim3, dim4) to a new shape (dim4, dim3, dim1, dim2). |
| 8 | +
|
| 9 | +Before permutation, we need to understand how to access elements in a flattened (linear) form of the matrix. |
| 10 | +
|
| 11 | +Given: |
| 12 | +
|
| 13 | +dim1 = size of the 1st dimension |
| 14 | +dim2 = size of the 2nd dimension |
| 15 | +dim3 = size of the 3rd dimension |
| 16 | +dim4 = size of the 4th dimension |
| 17 | +
|
| 18 | +For any element in a 4D matrix at position (i1, i2, i3, i4), where: |
| 19 | +
|
| 20 | +i1 is the index in dimension 1 |
| 21 | +i2 is the index in dimension 2 |
| 22 | +i3 is the index in dimension 3 |
| 23 | +i4 is the index in dimension 4 |
| 24 | +
|
| 25 | +If you find it challenging to calculate the indices i1, i2, i3, and i4, observe the pattern in the index calculations. |
| 26 | +Initially, it might take some time to grasp, but with practice, you'll develop a mental model for it. |
| 27 | +
|
| 28 | +To calculate the indices, use the following formulas: |
| 29 | +
|
| 30 | +i1 = (idx / (dim2 * dim3 * dim4)) % dim1; |
| 31 | +i2 = (idx / (dim3 * dim4)) % dim2; |
| 32 | +i3 = (idx / dim4) % dim3; |
| 33 | +i4 = idx % dim4; |
| 34 | +
|
| 35 | +Pattern Explanation: |
| 36 | +To find the index for any dimension, divide the thread ID (idx) by the product of all subsequent dimensions. |
| 37 | +Then, perform modulo operation with the current dimension. |
| 38 | +
|
| 39 | +
|
| 40 | +
|
| 41 | +The linear index in a flattened 1D array is calculated as: |
| 42 | +linear_idx = i1 × ( dim2 × dim3 × dim4 ) + i2 × ( dim3 × dim4 ) + i3 × dim4 + i4 |
| 43 | +This linear index uniquely identifies the position of the element in the 1D array. |
| 44 | +
|
| 45 | +To permute the matrix, we need to rearrange the indices according to the new shape. |
| 46 | +In this case, we are permuting from (dim1, dim2, dim3, dim4) to (dim4, dim3, dim1, dim2). |
| 47 | +
|
| 48 | +The new dimension post permutation will be as follows: |
| 49 | +
|
| 50 | +dim1 becomes the new 3rd dimension. |
| 51 | +dim2 becomes the new 4th dimension. |
| 52 | +dim3 becomes the new 2nd dimension. |
| 53 | +dim4 becomes the new 1st dimension. |
| 54 | +
|
| 55 | +permuted_idx = i4 * (dim3 * dim1 * dim2) + i3 * (dim1 * dim2) + i1 * dim2 + i2; |
| 56 | +
|
| 57 | +Here's how this works: |
| 58 | +
|
| 59 | +i4 * (dim3 * dim1 * dim2): This accounts for how many complete dim3 × dim1 × dim2 blocks fit before the current i4 block. |
| 60 | +i3 * (dim1 * dim2): This accounts for the offset within the current i4 block, specifying which i3 block we are in. |
| 61 | +i1 * dim2: This accounts for the offset within the current i3 block, specifying which i1 block we are in. |
| 62 | +i2: This gives the offset within the current i1 block. |
| 63 | +
|
| 64 | +Lastly at the end we store the current value at idx index of the original value to the permuted index in the permuted_matrix. |
| 65 | +
|
| 66 | +
|
| 67 | +-------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 68 | +
|
| 69 | +Similarly we can follow the above approach to permute matrices of any dimensions. |
| 70 | +
|
| 71 | +*/ |
| 72 | + |
| 73 | + |
| 74 | +#include <cuda_runtime.h> |
| 75 | +#include <stdio.h> |
| 76 | +#include <stdlib.h> |
| 77 | +#include <cmath> |
| 78 | + |
| 79 | +#include "common.h" |
| 80 | + |
| 81 | +// CPU function to permute a 4D matrix |
| 82 | +void permute_cpu(const float* matrix, float* out_matrix, int dim1, int dim2, int dim3, int dim4) { |
| 83 | + int total_threads = dim1 * dim2 * dim3 * dim4; |
| 84 | + |
| 85 | + for (int idx = 0; idx < total_threads; idx++) { |
| 86 | + // Calculate the 4D indices from the linear index |
| 87 | + int i1 = (idx / (dim2 * dim3 * dim4)) % dim1; |
| 88 | + int i2 = (idx / (dim3 * dim4)) % dim2; |
| 89 | + int i3 = (idx / dim4) % dim3; |
| 90 | + int i4 = idx % dim4; |
| 91 | + |
| 92 | + // Compute the new index for the permuted matrix |
| 93 | + // Transpose from (dim1, dim2, dim3, dim4) to (dim4, dim3, dim1, dim2) |
| 94 | + int permuted_idx = i4 * (dim3 * dim1 * dim2) + i3 * (dim1 * dim2) + i1 * dim2 + i2; |
| 95 | + out_matrix[permuted_idx] = matrix[idx]; |
| 96 | + } |
| 97 | +} |
| 98 | + |
| 99 | +// CUDA kernel to permute a 4D matrix |
| 100 | +__global__ void permute_kernel(const float* matrix, float* out_matrix, int dim1, int dim2, int dim3, int dim4) { |
| 101 | + int idx = blockIdx.x * blockDim.x + threadIdx.x; |
| 102 | + |
| 103 | + // Ensure index is within bounds |
| 104 | + if (idx < dim1 * dim2 * dim3 * dim4) { |
| 105 | + // Calculate the 4D indices from the linear index |
| 106 | + int i1 = (idx / (dim2 * dim3 * dim4)) % dim1; |
| 107 | + int i2 = (idx / (dim3 * dim4)) % dim2; |
| 108 | + int i3 = (idx / dim4) % dim3; |
| 109 | + int i4 = idx % dim4; |
| 110 | + |
| 111 | + // Compute the new index for the permuted matrix |
| 112 | + // Transpose from (dim1, dim2, dim3, dim4) to (dim4, dim3, dim1, dim2) |
| 113 | + int permuted_idx = i4 * (dim3 * dim1 * dim2) + i3 * (dim1 * dim2) + i1 * dim2 + i2; |
| 114 | + out_matrix[permuted_idx] = matrix[idx]; |
| 115 | + } |
| 116 | +} |
| 117 | + |
| 118 | + |
| 119 | +int main() { |
| 120 | + int dim_1 = 24; |
| 121 | + int dim_2 = 42; |
| 122 | + int dim_3 = 20; |
| 123 | + int dim_4 = 32; |
| 124 | + |
| 125 | + // Set up the device |
| 126 | + int deviceIdx = 0; |
| 127 | + cudaSetDevice(deviceIdx); |
| 128 | + cudaDeviceProp deviceProp; |
| 129 | + cudaGetDeviceProperties(&deviceProp, deviceIdx); |
| 130 | + printf("Device %d: %s\n", deviceIdx, deviceProp.name); |
| 131 | + |
| 132 | + // Allocate host memory |
| 133 | + float* matrix = make_random_float(dim_1 * dim_2 * dim_3 * dim_4); |
| 134 | + float* permuted_matrix = (float*)malloc(dim_1 * dim_2 * dim_3 * dim_4 * sizeof(float)); |
| 135 | + |
| 136 | + // Initialize the matrix with random values |
| 137 | + |
| 138 | + // Allocate device memory |
| 139 | + float *d_matrix, *d_permuted_matrix; |
| 140 | + cudaMalloc(&d_matrix, dim_1 * dim_2 * dim_3 * dim_4 * sizeof(float)); |
| 141 | + cudaMalloc(&d_permuted_matrix, dim_1 * dim_2 * dim_3 * dim_4 * sizeof(float)); |
| 142 | + |
| 143 | + // Copy matrix from host to device |
| 144 | + cudaMemcpy(d_matrix, matrix, dim_1 * dim_2 * dim_3 * dim_4 * sizeof(float), cudaMemcpyHostToDevice); |
| 145 | + |
| 146 | + // Perform permutation on CPU |
| 147 | + clock_t start = clock(); |
| 148 | + permute_cpu(matrix, permuted_matrix, dim_1, dim_2, dim_3, dim_4); |
| 149 | + clock_t end = clock(); |
| 150 | + double elapsed_time_cpu = (double)(end - start) / CLOCKS_PER_SEC; |
| 151 | + |
| 152 | + // Define block and grid sizes |
| 153 | + dim3 blockSize(256); |
| 154 | + int totalThreads = dim_1 * dim_2 * dim_3 * dim_4; |
| 155 | + int gridSize = (totalThreads + blockSize.x - 1) / blockSize.x; // Compute grid size |
| 156 | + |
| 157 | + // Launch CUDA kernel to perform permutation |
| 158 | + permute_kernel<<<gridSize, blockSize>>>(d_matrix, d_permuted_matrix, dim_1, dim_2, dim_3, dim_4); |
| 159 | + cudaDeviceSynchronize(); // Ensure kernel execution is complete |
| 160 | + |
| 161 | + // Verify results |
| 162 | + printf("Checking correctness...\n"); |
| 163 | + validate_result(d_permuted_matrix, permuted_matrix, "permuted_matrix", dim_1 * dim_2 * dim_3 * dim_4, 1e-5f); |
| 164 | + |
| 165 | + printf("All results match.\n\n"); |
| 166 | + // benchmark kernel |
| 167 | + int repeat_times = 1000; |
| 168 | + float elapsed_time = benchmark_kernel(repeat_times, permute_kernel, |
| 169 | + d_matrix, d_permuted_matrix, dim_1, dim_2, dim_3, dim_4 |
| 170 | + ); |
| 171 | + printf("time gpu %.4f ms\n", elapsed_time); |
| 172 | + printf("time cpu %.4f ms\n", elapsed_time_cpu); |
| 173 | + |
| 174 | + // Free allocated memory |
| 175 | + free(matrix); |
| 176 | + free(permuted_matrix); |
| 177 | + cudaFree(d_matrix); |
| 178 | + cudaFree(d_permuted_matrix); |
| 179 | + |
| 180 | + return 0; |
| 181 | +} |
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