how do I gather() a variable in atomicAdd()?

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I am just wondering how to return result from atomicAdd(), since atomicAdd only changes one of its inputs. Here is my kernel (CUDA C):
__global__ void agpuhelloworld( double* c, double ato, double b ) {
*c = ato + b;
atomicAdd(&ato, b);
I know how to collect c, but how do I collect value of ato from this kernel with a MATLAB script? I cannot declare that as persistent, because ato is one of the inputs to MATLAB function. Following is my MATLAB code, I think it is something like that. I only show how to gather() c.
function out = gpuhelloworld(ato,b)
persistent gpuadd;
persistent c;
if isempty(gpuadd)
disp 'Initializing GPU drf calculation...';
gpuadd = parallel.gpu.CUDAKernel('agpuhelloworld.ptx','','agpuhelloworld');
tmp = gpuDevice;
gpuadd.GridSize = [min(1024,tmp.MaxGridSize(1)) 1]; % min(1024, maxblocks)
gpuadd.ThreadBlockSize = [min(128,tmp.MaxThreadsPerBlock) 1 1]; % min(128, maxthreadsperblock)
c = gpuArray(zeros(1,1));
c= feval(gpuadd, c,ato,b);
out = gather(c);

Accepted Answer

m4 Chrennikov
m4 Chrennikov on 22 Mar 2012
Try this:
[c, ato] = feval(gpuadd, c,ato,b);
out = gather(ato);

More Answers (1)

Nick Tsui
Nick Tsui on 24 Mar 2012
Thanks it works.

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