Threads count stops

Accelerated Computing CUDA CUDA Programming and Performance
1

Hi,

I have a running kernel where I tried to increase number of threads that should be calculated. As I pass the limit of blocks in one direction, I want to set up a 2D grid. However it doesn’t work, I guess I forget a detail, but I can’t find it out what.

I want to launch 192192175 threads, so 6,451,200 threads. According to the information out of the deviceQuerry example I can launch 5126553565535, so I am way under this limit.

My kernel call looks like that:

#define n_bins (192*192*175)

    ...

     int numThreadsPerBlock=64;

     dim3 blocks(320,320); 

    pre_sum_calc<<<blocks, numThreadsPerBlock>>>(n_bins, xy_coords_d, z_coords_d, pre_sum_d, 

             BIN_events_d, y_i_d, y_k_d, x_j_d, x_back_d);

     cudaThreadSynchronize();

     checkCUDAError("pre_sum_calc invocation");

I calculate the thread ID in the kernel like that:

__global__ void pre_sum_calc(int n_bins, xy_struct* xy_coords, z_struct* z_coords,

         float* pre_sum, int* BIN_events, int* y_i, float* y_k, float* x_j, float* x_back)

{

   int tID = blockIdx.x*blockDim.x+blockIdx.y*gridDim.x*blockDim.x + threadIdx.x; //threadID

   int calc_type=0;

   if (tID<n_bins){

       int BIN = BIN_events[tID];

       get_BIN_data(BIN, calc_type, xy_coords,  z_coords,  pre_sum, y_i, y_k, x_j, x_back); //call to a device funtion

    }

}

So, I tired several sizes of each dimension of the grid, but the emulation mode always stops at the same thread ID = 1624064 . Device release returns an unspecific launch error.

Does anyone see what I am doing wrong here?

Thanks!

2

In my (limited) experience, ‘unspecified launch failure’ is equivalent to getting a segmentation fault when doing normal C/C++ coding. That being said, I would check to be sure you are not accessing data outside of your array. How large is BIN_events? Are you accessing any arrays inside of get_BIN_data and, if so, are you sure you’re accessing the correct indices?

3

Thanks a lot for the hint, you’re right!!! I haven’t seen that I still refer to the this array, in fact I don’t need it anymore, but somehow it was still there! External Media

Guess I should have a break! :)

Thanks, problems solved!