CODEWITHSUNDEEP
cuda
Atirag
Atirag

Reputation: 1750

Cudamemcpy function usage

How will the cudaMemcpy function work in this case?

I have declared a matrix like this 

float imagen[par->N][par->M];

and I want to copy it to the cuda device so I did this

float *imagen_cuda;

int tam_cuda=par->M*par->N*sizeof(float);

cudaMalloc((void**) &imagen_cuda,tam_cuda); 
cudaMemcpy(imagen_cuda,imagen,tam_cuda,cudaMemcpyHostToDevice);

Will this copy the 2d array into a 1d array fine?

And how can I copy to another 2d array? can I change this and will it work?

float **imagen_cuda;

Upvotes: 4

Views: 33180

Answers (1)

Robert Crovella
Robert Crovella

Reputation: 152184

It's not trivial to handle a doubly-subscripted C array when copying data between host and device. For the most part, cudaMemcpy (including cudaMemcpy2D) expect an ordinary pointer for source and destination, not a pointer-to-pointer.

The simplest approach (I think) is to "flatten" the 2D arrays, both on host and device, and use index arithmetic to simulate 2D coordinates:

float imagen[par->N][par->M];
float *myimagen = &(imagen[0][0]);
float myval = myimagen[(rowsize*row) + col];

You can then use ordinary cudaMemcpy operations to handle the transfers (using the myimagen pointer):

float *d_myimagen;
cudaMalloc((void **)&d_myimagen, (par->N * par->M)*sizeof(float));
cudaMemcpy(d_myimagen, myimagen, (par->N * par->M)*sizeof(float), cudaMemcpyHostToDevice);

If you really want to handle dynamically sized (i.e. not known at compile time) doubly-subscripted arrays, you can review this question/answer.

Upvotes: 5

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