increase vector with mex function

Hi *,

I would like to increase the values of a vector. I wrote two scripts:

incrementa.m

clc;

clear all;

global v

v = ones(100,1);

nvmex('incrementa.cu');

R = incrementa(v);

incrementa.cu:

#include mex.h

#include cuda.h

#include cuda_runtime.h

#include cmath

#include matrix.h

int *x,*Y;

_global_ void incrementa(int *x) {

for(int i=1; i<100; i++)

x[i] = x[i]++;

}

void fz_cuda() {

printf("sono in fz_cuda()\n");

int *device_x = NULL;

// Creating objects for the measurement of the times

cudaEvent_t start,stop;

float time;

cudaEventCreate(&start);

cudaEventCreate(&stop);

// Allocation on GPU

// INPUT:

if(cudaMalloc((void**) &device_x, 100*sizeof(int)) != cudaSuccess)

mexErrMsgTxt("Memory allocating of x failure on the GPU.");

// Copy on GPU

cudaMemcpy(device_x, x, 100*sizeof(int), cudaMemcpyHostToDevice);

// ==================== // Invoke CUDA kernel // ====================

cudaEventRecord(start,0);

incrementa<<<1,1>>>(device_x);

// Copy result on CPU

cudaMemcpy(x,device_x,100*sizeof(int), cudaMemcpyDeviceToHost);

// Memory free

cudaFree(device_x);

cudaEventElapsedTime(&time, start,stop);

printf ("Tempo per il kernel: %f ms\n", time);

}

void mexFunction(int nlhs, mxArray *plhs[],int nrhs, const mxArray *prhs[]) { // prhs[0] = v if (nrhs != 1)

mexErrMsgIdAndTxt("Invalid Input:nrhs","Require 1 inputs");

x = (int*)mxGetData(prhs[0]);

fz_cuda();

const mwSize outDims[2] = { 100,1 };

plhs[0] = mxCreateNumericArray(2, outDims, mxDOUBLE_CLASS, mxREAL);

    Y = (int*)mxGetData( plhs[0] );

}

but this doesn't work. Where I wrong?

Thanks, Davide

Answer 1

[James Tursa]

I don't know about the CUDA stuff, but you have a basic mismatch of types in your C code. E.g.,

v = ones(100,1);

The above creates a double matrix at the MATLAB level.

_global_ void incrementa(int *x) {
for(int i=1; i<100; i++)
x[i] = x[i]++;
}

The above increment routine expects a pointer to int.

x = (int*)mxGetData(prhs[0]);

The above line get a pointer to the input data as an int*, even though the input data is actually double.

plhs[0] = mxCreateNumericArray(2, outDims, mxDOUBLE_CLASS, mxREAL);
    Y = (int*)mxGetData( plhs[0] );

The above lines specifically create a double matrix, but you use an int* to get at the data.

So anything you do with this code will be hosed up as you are mixing int* with double data.