cudaMemcpyFromSymbol not getting the correct value back

Accelerated Computing CUDA CUDA Programming and Performance
1

Hi guys. I’ve got stucked here for a couple of days in this error. I have a Mac with a 320m, and I’m doing the following code:

__device__ float d_endAgents;

float h_endAgents;

void callingKernel(dim3 dimBlock dim3 dimThread){

	h_endAgents = -1.0;

	cudaMemset(&d_endAgents,-1.0,sizeof(float));

	

	

	kernel<<< dimBlock, dimThread >>> ();

	

        cudaThreadSynchronize());

	

	cudaMemcpyFromSymbol(&h_endAgents, "d_endAgents", sizeof(float),0, cudaMemcpyDeviceToHost);

	printf("\n[%f]", h_endAgents);

}

__global__ void kernel(){

	d_endAgents = -100.0;

}

This code returns to me that the value of d_endAgents is 0. I’ve tried many different ways to implement it, but all had the same anomaly. What can I do to return the correct value?

Sorry about any grammar mistakes

2

You can’t use the [font=“Courier New”]&[/font] operator in host code to obtain device addresses. You need to call [font=“Courier New”]cudaGetSymbolAddress()[/font] instead to obtain the address.

It’s just the same as you cannot write

cudaMemcpy(&h_endAgents, &d_endAgents, sizeof(float),cudaMemcpyDeviceToHost);

but need to use

cudaMemcpyFromSymbol(&h_endAgents, "d_endAgents", sizeof(float),0, cudaMemcpyDeviceToHost);

instead.

3

Doing some modifications here since yesterday I’ve found the problem. When I was using the dim3 var to specify the number of threads and blocks for some reason the kernel wasn’t lauching well. I’ve changed it to <<< 1, 16 >>> and it worked somehow. I’m investigating it. Thanks Tera