![enter image description here](https://i.stack.imgur.com/gsxsF.jpg)
正如你可以看到現在,默認流執行與其他兩個流的執行重疊。
#include <iostream>
#include "cuda_runtime.h"
#include "device_launch_parameters.h"
#include <stdio.h>
#include "Utilities.cuh"
using namespace std;
#define NUM_THREADS 32
#define NUM_BLOCKS 16
#define NUM_STREAMS 3
__global__ void kernel(const int *in, int *out, int N)
{
int start = blockIdx.x * blockDim.x + threadIdx.x;
int end = N;
for (int i = start; i < end; i += blockDim.x * gridDim.x)
{
out[i] = in[i] * in[i];
}
}
int main()
{
const int N = 6000000;
// --- Host side input data allocation and initialization. Registering host memory as page-locked (required for asynch cudaMemcpyAsync).
int *h_in = new int[N]; for(int i = 0; i < N; i++) h_in[i] = 5;
gpuErrchk(cudaHostRegister(h_in, N * sizeof(int), cudaHostRegisterPortable));
// --- Host side input data allocation and initialization. Registering host memory as page-locked (required for asynch cudaMemcpyAsync).
int *h_out = new int[N]; for(int i = 0; i < N; i++) h_out[i] = 0;
gpuErrchk(cudaHostRegister(h_out, N * sizeof(int), cudaHostRegisterPortable));
// --- Host side check results vector allocation and initialization
int *h_checkResults = new int[N]; for(int i = 0; i < N; i++) h_checkResults[i] = h_in[i] * h_in[i];
// --- Device side input data allocation.
int *d_in = 0; gpuErrchk(cudaMalloc((void **)&d_in, N * sizeof(int)));
// --- Device side output data allocation.
int *d_out = 0; gpuErrchk(cudaMalloc((void **)&d_out, N * sizeof(int)));
int streamSize = N/NUM_STREAMS;
size_t streamMemSize = N * sizeof(int)/NUM_STREAMS;
// --- Set kernel launch configuration
dim3 nThreads = dim3(NUM_THREADS,1,1);
dim3 nBlocks = dim3(NUM_BLOCKS, 1,1);
dim3 subKernelBlock = dim3((int)ceil((float)nBlocks.x/2));
// --- Create CUDA streams
cudaStream_t streams[NUM_STREAMS];
for(int i = 0; i < NUM_STREAMS; i++)
gpuErrchk(cudaStreamCreate(&streams[i]));
/**************************/
/* BREADTH-FIRST APPROACH */
/**************************/
int offset = 0;
cudaMemcpyAsync(&d_in[offset], &h_in[offset], streamMemSize, cudaMemcpyHostToDevice, 0);
for(int i = 1; i < NUM_STREAMS; i++) {
int offset = i * streamSize;
cudaMemcpyAsync(&d_in[offset], &h_in[offset], streamMemSize, cudaMemcpyHostToDevice, streams[i]);
}
kernel<<<subKernelBlock, nThreads>>>(&d_in[offset], &d_out[offset], streamSize/2);
kernel<<<subKernelBlock, nThreads>>>(&d_in[offset + streamSize/2], &d_out[offset + streamSize/2], streamSize/2);
for(int i = 1; i < NUM_STREAMS; i++)
{
int offset = i * streamSize;
kernel<<<subKernelBlock, nThreads, 0, streams[i]>>>(&d_in[offset], &d_out[offset], streamSize/2);
kernel<<<subKernelBlock, nThreads, 0, streams[i]>>>(&d_in[offset + streamSize/2], &d_out[offset + streamSize/2], streamSize/2);
}
for(int i = 1; i < NUM_STREAMS; i++) {
int offset = i * streamSize;
cudaMemcpyAsync(&h_out[offset], &d_out[offset], streamMemSize, cudaMemcpyDeviceToHost, streams[i]);
}
cudaMemcpyAsync(&h_out[offset], &d_out[offset], streamMemSize, cudaMemcpyDeviceToHost, 0);
for(int i = 1; i < NUM_STREAMS; i++) {
int offset = i * streamSize;
cudaMemcpyAsync(&h_out[offset], &d_out[offset], streamMemSize, cudaMemcpyDeviceToHost, 0);
}
for(int i = 0; i < NUM_STREAMS; i++)
gpuErrchk(cudaStreamSynchronize(streams[i]));
gpuErrchk(cudaDeviceSynchronize());
// --- Release resources
gpuErrchk(cudaHostUnregister(h_in));
gpuErrchk(cudaHostUnregister(h_out));
gpuErrchk(cudaFree(d_in));
gpuErrchk(cudaFree(d_out));
for(int i = 0; i < NUM_STREAMS; i++)
gpuErrchk(cudaStreamDestroy(streams[i]));
cudaDeviceReset();
// --- GPU output check
int sum = 0;
for(int i = 0; i < N; i++)
sum += h_checkResults[i] - h_out[i];
cout << "Error between CPU and GPU: " << sum << endl;
delete[] h_in;
delete[] h_out;
delete[] h_checkResults;
return 0;
}