#include <pthread.h>
#include <cuda.h>
float *x, *y;
#define PROC (8)
float e_vec[PROC];
int n_thread0, n_thread1;
// kernel
__global__ void sub1(float* fx, float* fy, float* fe) {
#define BLOCK (512)
int t = threadIdx.x; // builtin
int b = blockIdx.x; // builtin
float e;
__shared__ float se[BLOCK];
__shared__ float sx[BLOCK];
__shared__ float sy[BLOCK+2];
// copy from device to processor memory
sx[t] = fx[BLOCK*b+t];
sy[t] = fy[BLOCK*b+t];
if (t<2)
sy[t+BLOCK] = fy[BLOCK*b+t+BLOCK];
__syncthreads();
// do computation
sx[t] += ( sy[t+2] + sy[t] )*.5;
e = sy[t+1] * sy[t+1];
// copy to device memory
fx[BLOCK*b+t] = sx[t];
// reduction
se[t] = e;
__syncthreads();
if (t<256) {
se[t] += se[t+256];
__syncthreads();
}
if (t<128) {
se[t] += se[t+128];
__syncthreads();
}
if (t<64) {
se[t] += se[t+64];
__syncthreads();
}
if (t<32) { // warp size
se[t] += se[t+32];
se[t] += se[t+16];
se[t] += se[t+8];
se[t] += se[t+4];
se[t] += se[t+2];
se[t] += se[t+1];
}
if (t==0)
fe[b] = se[0];
}
void *thread1(void *arg) {
int p = (int)arg;
int n0 = n_thread0 + (p * (n_thread1-n_thread0)) / PROC;
int n1 = n_thread0 + ((p+1) * (n_thread1-n_thread0)) / PROC;
// pick GPU
cudaSetDevice(p);
// allocate GPU memory
float *fx, *fy, *fe;
cudaMalloc((void**)&fx, (n1-n0+2) * sizeof(float));
cudaMalloc((void**)&fy, (n1-n0+2) * sizeof(float));
cudaMalloc((void**)&fe, (n1-n0+2)/BLOCK * sizeof(float));
float *de = new float[(n1-n0+2)/BLOCK];
// copy to GPU memory
cudaMemcpy(fx+1, &x[n0],
(n1-n0) * sizeof(float), cudaMemcpyHostToDevice);
cudaMemcpy(fy, &y[n0-1],
(n1-n0+2) * sizeof(float), cudaMemcpyHostToDevice);
dim3 dimBlock(BLOCK, 1, 1);
dim3 dimGrid((n1-n0+2)/BLOCK, 1, 1);
float e = 0;
// call GPU
sub1<<<dimGrid, dimBlock>>>(fx, fy, fe);
// copy to host memory
cudaMemcpy(fx+1, &x[n0], (n1-n0) * sizeof(float),
cudaMemcpyDeviceToHost);
cudaMemcpy(fe, &de[n0-1], (n1-n0+2)/BLOCK * sizeof(float),
cudaMemcpyDeviceToHost);
// release GPU memory
cudaFree(fe);
cudaFree(fy);
cudaFree(fx);
float e_local = 0;
for (int i=0; i<(n1-n0+2)/BLOCK; ++i)
e_local += de[i];
e += e_local;
delete[] de;
e_vec[p] = e;
return (void*) 0;
}
int main(int argc, char *argv[]) {
int n = ...;
float *x, *y;
x = new float[n+1];
y = new float[n+1];
... // fill x, y
pthread_t threads[PROC];
pthread_attr_t attr;
pthread_attr_init(&attr);
n_thread0 = 1;
n_thread1 = n;
float e = 0;
// start threads and wait for termination
for (int p=0; p<PROC; ++p)
pthread_create(&threads[p], &attr, thread1, (void *)p);
for (int p=0; p<PROC; ++p) {
pthread_join(threads[p], NULL);
e += e_vec[p];
}
... // output x, e
delete[] x, y;
return 0;
}
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