Problem with get_global_id(1);


I’m struggling to get two dimensional workgroups to work, and it might be due to a bug in Nvidia’s OpenCL implementation.

Spec-wise I’m on Ubuntu Linux 12.04 with NVIDIA driver 331.20 and a Quadro 600 (yeah I know, I’m looking to get a new graphics card!) and OpenCL 1.1 (installed via apt-get install nvidia-opencl-dev).

If I run this simple kernel:

__kernel void test2Dim(
    __global uint* field)
    size_t id = get_global_id(1)*get_global_size(0) + get_global_id(0);
    field[id] = id;

And then on C++ I execute the following (assume context, queue and program have been properly initialised, I have checked).

cl::Kernel twoDimTest = cl::Kernel(program, "test2Dim");
cl::Buffer twoDimBuffer = cl::Buffer(

twoDimTest.setArg(0, twoDimBuffer);

queue.enqueueNDRangeKernel(twoDimTest, 0, cl::NDRange(2,2), cl::NDRange(2,1));

cl_uint array[4];

queue.enqueueReadBuffer(twoDimBuffer, true, 0, 4*sizeof(cl_uint), array);

std::cout << array[0] << " " << array[1] << " " 
          << array[2] << " " << array[3] << std::endl;

I would expect the output to be “0 1 2 3”, instead I get a cl::Error exception “clEnqueueReadBuffer” -5 (CL_OUT_OF_RESOURCES). I think the kernel is writing all over the place.

If I launch the kernel this way however:

queue.enqueueNDRangeKernel(twoDimTest, 0, cl::NDRange(4), cl::NDRange(1));

The output is “0 1 2 3” as expected and no exceptions are thrown.

Using 2D workgroups seems like a common task for GPGPU, but I haven’t been able to find anyone online with a similar issue.

Am I doing something wrong? Or is it indeed a bug? And if so, is it a known issue?


Does the same code work correctly if you try it on another OpenCL CPU/GPU? (e.g. your Intel/AMD CPU, or another GPU)

You might need to install either the AMD APP SDK:

or the Intel OpenCL SDK: to do so.

I installed both and the AMD SDK is the easiest to install – no need to convert RPM packages to DEB (see post by Noah R.) to install under Ubuntu. The AMD APP OpenCL SDK will work on both Intel and AMD processors… it just won’t support some advanced extensions that the Intel version provides if you have an Intel processor.

Also, you can find other OpenCL 2D samples online and see if they behave correctly as well.


Thanks for your quick reply.

I had an old iMac lying around with OpenCL compatibility so I went and run the code there :) For what is worth it was an OSX 10.9.3 machine with ATI RadeonHD 4850 512MB, and OpenCL 1.0 compatibility.

On the iMac the code above always replies “0 1 2 3” (the correct solution) independently of whether I use one or two dimensions.

I also tried with with Ubuntu 14.04 and the Nvidia driver 331.38 and the error still occurs.

Will now try to look for a 2D sample as you suggested and report back…

Okay, I figured it out. I installed the OpenCL examples ( and found that oclTranspose was using two dimensions like I did.

Moreover the C-API version of the enqueueNDRangeKernel worked on my example, and so I eventually found the error: in the C++ API offset is of type cl::NDRange() and it should be called like this:

queue.enqueueNDRangeKernel(twoDimTest, cl::NDRange(), cl::NDRange(2,2), cl::NDRange(2,1));

Note the only difference is that cl::NDRange() replaces a 0. That’s it! Thinking about it, it’s a bit surprising that the previous code run well on the iMac…

Thanks for the help!

If you wish to provide a complete code along with compile instructions, I’ll be happy to try it.

Here’s my version of what you posted, it seems to work correctly for me:

// OpenCL Kernel Function for 2D kernel test

__kernel void test2Dim(
__global uint* field)
  size_t id = get_global_id(1)*get_global_size(0) + get_global_id(0);
  field[id] = id;


// *********************************************************************
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <CL/opencl.h>

//! Loads a Program file and prepends the cPreamble to the code.
//! @return the source string if succeeded, 0 otherwise
//! @param cFilename        program filename
//! @param cPreamble        code that is prepended to the loaded file, typicall
a set of #defines or a header
//! @param szFinalLength    returned length of the code string
char* oclLoadProgSource(const char* cFilename, const char* cPreamble, size_t* sz
    // locals
    FILE* pFileStream = NULL;
    size_t szSourceLength;

    // open the OpenCL source code file
    #ifdef _WIN32   // Windows version
        if(fopen_s(&pFileStream, cFilename, "rb") != 0)
            return NULL;
    #else           // Linux version
        pFileStream = fopen(cFilename, "rb");
        if(pFileStream == 0)
            return NULL;

    size_t szPreambleLength = strlen(cPreamble);

    // get the length of the source code
    fseek(pFileStream, 0, SEEK_END);
    szSourceLength = ftell(pFileStream);
    fseek(pFileStream, 0, SEEK_SET);

    // allocate a buffer for the source code string and read it in
    char* cSourceString = (char *)malloc(szSourceLength + szPreambleLength + 1);

    memcpy(cSourceString, cPreamble, szPreambleLength);
    if (fread((cSourceString) + szPreambleLength, szSourceLength, 1, pFileStream
) != 1)
        return 0;

    // close the file and return the total length of the combined (preamble + source) string
    if(szFinalLength != 0)
        *szFinalLength = szSourceLength + szPreambleLength;
    cSourceString[szSourceLength + szPreambleLength] = '\0';

    return cSourceString;

// Name of the file with the source code for the computation kernel
// *********************************************************************
const char* cSourceFile = "";

// Host buffers for demo
// *********************************************************************
void *srcA;   // Host buffers for OpenCL test

// OpenCL Vars
cl_context cxGPUContext;        // OpenCL context
cl_command_queue cqCommandQueue;// OpenCL command que
cl_platform_id cpPlatform;      // OpenCL platform
cl_device_id cdDevice;          // OpenCL device
cl_program cpProgram;           // OpenCL program
cl_kernel ckKernel;             // OpenCL kernel
cl_mem cmDevSrcA;               // OpenCL device source buffer A
size_t szGlobalWorkSize[2];        // 1D var for Total # of work items
size_t szLocalWorkSize[2];         // 1D var for # of work items in the work group
size_t szParmDataBytes;                 // Byte size of context information
size_t szKernelLength;                  // Byte size of kernel code
cl_int ciErr1, ciErr2;                  // Error code var
char* cPathAndName = NULL;      // var for full paths to data, src, etc.
char* cSourceCL = NULL;         // Buffer to hold source for compilation

// demo config vars
int iNumElements = 4;    // Length of float arrays to process

// Forward Declarations
// *********************************************************************
void Cleanup (int iExitCode);

// Main function
// *********************************************************************
int main(int argc, char **argv)

    printf("%s Starting...\n\n# of elements \t= %i\n", argv[0], iNumElements);

    // Allocate and initialize host arrays
    printf( "Allocate and Init Host Mem...\n");
    srcA = (void *)malloc(sizeof(cl_uint) * iNumElements);

    //Get an OpenCL platform
    ciErr1 = clGetPlatformIDs(1, &cpPlatform, NULL);

    if (ciErr1 != CL_SUCCESS)
        printf("Error in clGetPlatformID, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    //Get the devices
    ciErr1 = clGetDeviceIDs(cpPlatform, CL_DEVICE_TYPE_GPU, 1, &cdDevice, NULL);
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clGetDeviceIDs, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    //Create the context
    cxGPUContext = clCreateContext(0, 1, &cdDevice, NULL, NULL, &ciErr1);
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clCreateContext, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // Create a command-queue
    cqCommandQueue = clCreateCommandQueue(cxGPUContext, cdDevice, 0, &ciErr1);
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clCreateCommandQueue, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // Allocate the OpenCL buffer memory objects for source and result on the device GMEM
    cmDevSrcA = clCreateBuffer(cxGPUContext, CL_MEM_WRITE_ONLY, sizeof(cl_uint) * iNumElements, NULL, &ciErr1);
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clCreateBuffer, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // Read the OpenCL kernel in from source file
    printf("oclLoadProgSource (%s)...\n", cSourceFile);
    cPathAndName = "./";
    cSourceCL = oclLoadProgSource(cPathAndName, "", &szKernelLength);

    // Create the program
    cpProgram = clCreateProgramWithSource(cxGPUContext, 1, (const char **)&cSourceCL, &szKernelLength, &ciErr1);
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clCreateProgramWithSource, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // Build the program with 'mad' Optimization option
    char* flags = "-cl-fast-relaxed-math";
    ciErr1 = clBuildProgram(cpProgram, 0, NULL, NULL, NULL, NULL);
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clBuildProgram, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // Create the kernel
    ckKernel = clCreateKernel(cpProgram, "test2Dim", &ciErr1);
    printf("clCreateKernel (test2Dim)...\n");
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clCreateKernel, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // Set the Argument values
    ciErr1 = clSetKernelArg(ckKernel, 0, sizeof(cl_mem), (void*)&cmDevSrcA);
    printf("clSetKernelArg 0 ...\n\n");
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clSetKernelArg, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // --------------------------------------------------------
    // Start Core sequence... compute, copy results back
    szGlobalWorkSize[0] = 2;
    szGlobalWorkSize[1] = 2;
    szLocalWorkSize[0] = 2;
    szLocalWorkSize[1] = 2;

    // Launch kernel
    ciErr1 = clEnqueueNDRangeKernel(cqCommandQueue, ckKernel, 2, NULL, szGlobalWorkSize, szLocalWorkSize, 0, NULL, NULL);
    printf("clEnqueueNDRangeKernel (test2Dim)...\n");
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clEnqueueNDRangeKernel, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // Synchronous/blocking read of results, and check accumulated errors
    ciErr1 = clEnqueueReadBuffer(cqCommandQueue, cmDevSrcA, CL_TRUE, 0, sizeof(cl_uint) * iNumElements, srcA, 0, NULL, NULL);
    printf("clEnqueueReadBuffer (srcA)...\n\n");
    if (ciErr1 != CL_SUCCESS)
        printf("Error in clEnqueueReadBuffer, Line %u in file %s !!!\n\n", __LINE__, __FILE__);

    // print results 
    for (int i = 0; i < iNumElements; i++)
      printf("srcA[%d] = %d\n",i, *((uint *)srcA+i));
    // Cleanup and leave
    Cleanup (EXIT_SUCCESS);

void Cleanup (int iExitCode)
    // Cleanup allocated objects
    printf("Starting Cleanup...\n\n");

    // Free host memory
    exit (iExitCode);


g++ -L/usr/lib64 -lOpenCL -I/usr/local/cuda/include -o t3 t3.cpp

(using CUDA 6 standard linux install)


$ ./t3
./t3 Starting...

# of elements   = 4
Allocate and Init Host Mem...
oclLoadProgSource (
clCreateKernel (test2Dim)...
clSetKernelArg 0 ...

clEnqueueNDRangeKernel (test2Dim)...
clEnqueueReadBuffer (srcA)...

srcA[0] = 0
srcA[1] = 1
srcA[2] = 2
srcA[3] = 3
Starting Cleanup...

I think while I was editing my answer before posting it, you posted your answer. I’m glad you figured it out.