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enqueueNDRangeKernel / Invalid work group size error

Question asked by atoz on Jun 4, 2013
Latest reply on Jun 4, 2013 by atoz



i am trying to use opencl (api 1.2) on a bit older hardware and software - socket am3 cpu/a 5770 and a 6550 gpu, debian/squeeze w. 3.2 backports kernel and amd-driver version 12.4 <-- i use this outdated driver because of the old xorg version in debian/squeeze.


i use the enqueueNDRangeKernel method from the queue object to start a simple matrix multiplication kernel with different numbers of threads to get a feeling for the necessary number of threads for this device and i am experiencing the following problem:


if i use the following call it works like a charm, but only utilizing one compute module on the gpu/one core on the CPU:

queue->enqueueNDRangeKernel(*kernel, cl::NullRange, numThreads, cl::nullRange, NULL, &event);


numThreads ... total number of threads.


if i try to speficy the global and local dimenstion:

queue->enqueueNDRangeKernel(*kernel, cl::NullRange, numThreads, threadsPerWorkgroup, NULL, &event);


numThreads ... still total number of threads

threadsPerWorkgroup ... at the moment fixated to 16


i get an error "Invalid work group size".


i thought the opencl library will select a proper layout for the device automatically


can anyone give me some hints to resolve this problem?