__shfl_up_sync()

up 是指 從取值的線程對齊。

#include <cuda_runtime.h> #include <stdio.h> #define warpSize 32__global__ void scan4(float* a, float* b) {int laneId = threadIdx.x & 0x1f;float value;value = a[laneId];value = __shfl_up_sync(0xffffffff, value, 4);b[laneId] = value; }void printVector(char* desc, float* ptr_vec, unsigned int n){printf("%s =\n", desc);for(int i=0; i<n; i++){printf(" %5.2f ",ptr_vec[i]);}printf("\n"); }int main() {float* a_h = NULL;float* a_d = NULL;float* b_h = NULL;float* b_d = NULL;a_h = (float*)malloc(warpSize*sizeof(float));b_h = (float*)malloc(warpSize*sizeof(float));for(int i=0; i<warpSize; i++){a_h[i] = i+100.0;}//memset(b_h, 15, warpSize*sizeof(float));for(int i=0; i<warpSize; i++){b_h[i] = i+100.0;}printVector("a_h",a_h, warpSize);printVector("b_h",b_h, warpSize);cudaMalloc((void**)&a_d, warpSize*sizeof(float));cudaMalloc((void**)&b_d, warpSize*sizeof(float));cudaMemcpy(a_d, a_h, warpSize*sizeof(float), cudaMemcpyHostToDevice); cudaMemcpy(b_d, b_h, warpSize*sizeof(float), cudaMemcpyHostToDevice); scan4<<< 1, warpSize >>>(a_d, b_d);cudaDeviceSynchronize();cudaMemcpy(b_h, b_d, warpSize*sizeof(float), cudaMemcpyDeviceToHost);printVector("b_d", b_h, warpSize);cudaFree(a_d);cudaFree(b_d);return 0; }

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