“invalid configuration argument ” error for the call of CUDA kernel?

Question

Here is my code:

int threadNum = BLOCKDIM/8;
dim3 dimBlock(threadNum,threadNum);
int blocks1 = nWidth/threadNum + (nWidth%threadNum == 0 ? 0 : 1);
int blocks         


        

Answer 1

Just to add to the previous answers, you can find the max threads allowed in your code also, so it can run in other devices without hard-coding the number of threads you will use:

struct cudaDeviceProp properties;
cudaGetDeviceProperties(&properties, device);
cout<<"using "<<properties.multiProcessorCount<<" multiprocessors"<<endl;
cout<<"max threads per processor: "<<properties.maxThreadsPerMultiProcessor<<endl;

Answer 2

This type of error message frequently refers to the launch configuration parameters (grid/threadblock dimensions in this case, could also be shared memory, etc. in other cases). When you see a message like this it's a good idea just to print out your actual config parameters before launching the kernel, to see if you've made any mistakes.

You said BLOCKDIM = 512. You have threadNum = BLOCKDIM/8 so threadNum = 64. Your threadblock configuration is:

dim3 dimBlock(threadNum,threadNum);

So you are asking to launch blocks of 64 x 64 threads, that is 4096 threads per block. That won't work on any generation of CUDA devices. All current CUDA devices are limited to a maximum of 1024 threads per block, which is the product of the 3 block dimensions.

Maximum dimensions are listed in table 14 of the CUDA programming guide, and also available via the deviceQuery CUDA sample code.