I have this serial code that I'm trying to convert to parallel using MPI. However I can't seem to get the MPI_Scatter() function to work correctly without crashing. The function loops over an array called cells and modifies some of the values.
Below is the original serial code:
int accelerate_flow(const t_param params, t_speed* cells, int* obstacles) { register int ii,jj; /* generic counters */ register float w1,w2; /* weighting factors */ /* compute weighting factors */ w1 = params.density * params.accel * oneover9; w2 = params.density * params.accel * oneover36; int i; /* modify the first column of the grid */ jj=0; for(ii=0;ii<params.ny;ii++) { if( !obstacles[ii*params.nx] && (cells[ii*params.nx].speeds[3] > w1 && cells[ii*params.nx].speeds[6] > w2 && cells[ii*params.nx].speeds[7] > w2)) { /* increase 'east-side' densities */ cells[ii*params.nx].speeds[1] += w1; cells[ii*params.nx].speeds[5] += w2; cells[ii*params.nx].speeds[8] += w2; /* decrease 'west-side' densities */ cells[ii*params.nx].speeds[3] -= w1; cells[ii*params.nx].speeds[6] -= w2; cells[ii*params.nx].speeds[7] -= w2; } } return EXIT_SUCCESS; } And here is my attempt at using MPI:
int accelerate_flow(const t_param params, t_speed* cells, int* obstacles, int myrank, int ntasks) { register int ii,jj = 0;; /* generic counters */ register float w1,w2; /* weighting factors */ int recvSize; int cellsSendTag = 123, cellsRecvTag = 321; int size = params.ny / ntasks, i; MPI_Request* cellsSend, *cellsRecieve; MPI_Status *status; /* compute weighting factors */ w1 = params.density * params.accel * oneover9; w2 = params.density * params.accel * oneover36; t_speed* recvCells = (t_speed*)malloc(size*sizeof(t_speed)*params.nx); MPI_Scatter(cells, sizeof(t_speed)*params.nx*params.ny, MPI_BYTE, recvCells, size*sizeof(t_speed)*params.nx, MPI_BYTE, 0, MPI_COMM_WORLD); for(ii= 0;ii < size;ii++) { if( !obstacles[ii*params.nx] && (recvCells[ii*params.nx].speeds[3] > w1 && recvCells[ii*params.nx].speeds[6] > w2 && recvCells[ii*params.nx].speeds[7] > w2)) { /* increase 'east-side' densities */ recvCells[ii*params.nx].speeds[1] += w1; recvCells[ii*params.nx].speeds[5] += w2; recvCells[ii*params.nx].speeds[8] += w2; /* decrease 'west-side' densities */ recvCells[ii*params.nx].speeds[3] -= w1; recvCells[ii*params.nx].speeds[6] -= w2; recvCells[ii*params.nx].speeds[7] -= w2; } } MPI_Gather(recvCells, size*sizeof(t_speed)*params.nx, MPI_BYTE, cells, params.ny*sizeof(t_speed)*params.nx, MPI_BYTE, 0, MPI_COMM_WORLD); return EXIT_SUCCESS; } And here is the t_speed structure:
typedef struct { float speeds[NSPEEDS]; } t_speed; params.nx = 300, params.ny = 200
Would greatly appreciate any help. Thanks.
