Passing a vector of structure to the device I need help about how to pass a std::vector<structure

Accelerated Computing CUDA CUDA Programming and Performance
#1

Hello,

I’ve got a problem. I’d like to pass a vector of structure from the host to the device, in order to do some computation on it, and then pass it back to the host.

I’m using a std::vector of a custom structure. Here is my code :

#include <iostream>

#include <string>

#include <vector>

#include <cuda.h>

using namespace std;

//STRUCTURE DEFINITION

struct prgm_structure

{

	string name;

	int fitness;

};

//VECTOR DEFINITION

typedef vector<prgm_structure> prgm_vector;

//KERNELL FUNCTION

__global__ void calcul_fitness_GPU_Device(prgm_vector* population)

{

	int fitness;

	fitness = population[threadIdx.x].fitness;

}

//MAIN FUNCTION

int main()

{

	//Creation and initialisation of the vector "population_Host"

	prgm_vector population_Host;

	initialisation_population(population_Host);

	//Allocation and load of the vector "population_Device"

	prgm_vector* population_Device;

	int size = population_Host.size() * sizeof(prgm_structure);

	cudaMalloc((void**)&population_Device, size);

	cudaMemcpy(population_Device, &population_Host, size, cudaMemcpyHostToDevice);

	//Call of the kernell function

	dim3 dimBlock(16);

	dim3 dimGrid(1);

	calcul_fitness_GPU_Device<<<dimGrid, dimBlock>>>(population_Device);

}

This code doesn’t compile. I don’t manage to access the elements of the vector once in the kernell. I got an error at this line in the kernell :

fitness = population[threadIdx.x].fitness;

The error is :

If change this line to :

fitness = population.at(threadIdx.x).fitness;

The error become :

And if i change it again to :

fitness = population->at(threadIdx.x).fitness;

Then the error become :

I don’t understand, and i’ve no more idea… :">

Is it possible to pass a vector of structure to the device kernell? If yes, does somebody know how to correct my code?

Thanks :thumbup:

++

#2

An std::vector, unless you use a custom allocator, only holds host memory. Use a pointer instead, or use the vector class in the CUPP project

//VECTOR DEFINITION

typedef vector<prgm_structure> prgm_vector;  // for host memory only!!!

//KERNELL FUNCTION

__global__ void calcul_fitness_GPU_Device(prgm_structure* population)

{

	int fitness = population[threadIdx.x].fitness;

}

//MAIN FUNCTION

int main()

{

	//Creation and initialisation of the vector "population_Host"

	prgm_vector population_Host;

	initialisation_population(population_Host);

	//Allocation and load of the vector "population_Device"

	prgm_structure* population_Device;

	int size = population_Host.size() * sizeof(prgm_structure);

	cudaMalloc((void**)&population_Device, size);

	cudaMemcpy(population_Device, &population_Host[0], size, cudaMemcpyHostToDevice);

	//Call of the kernell function

	dim3 dimBlock(16);

	dim3 dimGrid(1);

	calcul_fitness_GPU_Device<<<dimGrid, dimBlock>>>(population_Device);

}

You should also try to make sure you are not accessing memory outside what you allocated.

#3

Thanks for your reply.

How would you do using a pointer instead of a vector? I already use a pointer, don’t I?

++

#4

The address of the first element in the vector, not the address of the vector itself, is the pointer to the underlying array that you can memcopy. In *rocha’s code, it’s this part
cudaMemcpy(population_Device, &population_Host[0], size, cudaMemcpyHostToDevice);
Note taking address of the [0] element

#5

OK, thanks. I didn’t noticed this change

I will try this.

Thanks for your help

#6

//KERNELL FUNCTION
global void calcul_fitness_GPU_Device(prgm_structure* population)
{
int fitness = population[threadIdx.x].fitness;
}

I suposse you are wrong here. The structure was not needed to be passed instead the whole vector was to be passed.

#7

Hello,

No it works. No need to pass the whole vector : the adress of its first element is enough. If you know the adress of the first element, you can access the following ones…

Thanks

#8

Just stick with ANSI-C:

//STRUCTURE DEFINITION

typedef struct prgm_structure

{

	string name;

	int fitness;

} prgm_vector;

or

//STRUCTURE DEFINITION

struct prgm_structure

{

	string name;

	int fitness;

};

//VECTOR DEFINITION

typedef struct prgm_structure prgm_vector;