Ah yes, thanks Karl. I remember that now. With that said, are there
recommendations on how kernels should be written to address the padded
columns? I am imagining some if/else or loop limits on indices but thought
I would ask here before I start trying to do that. I am trying to look
through the kernels and I am seeing things along the lines of
'global_size(0) < size' where I assume size refers to one of the dimensions?
If so, I humbly recommend that although the padding is mentioned with
respect to the matrix types either an example or explanation would be
valuable in the custom kernel section (at the very least another friendly
reminder). Not all repetition is bad :)
Thanks,
Charles
On Mon, May 23, 2016 at 2:03 PM, Karl Rupp <r...@iue.tuwien.ac.at> wrote:
> Hi,
>
>
> On 05/23/2016 05:38 PM, Charles Determan wrote:
>
>> I am experimenting with the custom OpenCL kernel functionality,
>> specifically a naive matrix multiplication as an example.
>>
>> My OpenCL Kernel:
>> __kernel void iMatMult(const int Mdim, const int Pdim,
>> __global const int *A, __global const int *B,
>> __global int *C) {
>>
>> // Get the index of the elements to be processed
>> const int globalRow = get_global_id(0); // C Row ID
>> const int globalCol = get_global_id(1); // C Col ID
>> int tmp = 0;
>>
>> // Do the operation
>> for(int k=0; k < Pdim; k++){
>> tmp += A[k*Mdim+globalRow] * B[globalCol*Pdim+k];
>> }
>> C[globalCol*Mdim+globalRow] = tmp;
>> }
>>
>>
>> Relevant C++ code
>> where vcl_* refer to viennacl::matrix<int>
>> and my_kernel is a string referring to the kernel above:
>>
>> int M = vcl_A.size2();
>> int P = vcl_A.size1();
>>
>> // add kernel to program
>> viennacl::ocl::program & my_prog =
>> viennacl::ocl::current_context().add_program(my_kernel, "my_kernel");
>>
>> // get compiled kernel function
>> viennacl::ocl::kernel & my_kernel_mul =
>> my_prog.get_kernel("iMatMult");
>>
>> // execute kernel
>> viennacl::ocl::enqueue(my_kernel_mul(M, P, vcl_A, vcl_B, vcl_C));
>>
>>
>> Oddly, the results in the vcl_C object are incorrect. But if I manually
>> go through the OpenCL using the C++ API the results are correct (which
>> you can see the API code here
>> https://github.com/cdeterman/gpuR/blob/develop/src/gpuMatrix_igemm.cpp).
>> Did
>> I miss something?
>>
>
> yes, you missed the internal data layout: rows/columns may be padded with
> zeros:
> http://viennacl.sourceforge.net/doc/manual-types.html#manual-types-matrix
> (this has performance reasons, but it is - unfortunately - often
> overlooked by users)
>
> Best regards,
> Karli
>
>
>
>
>
>>
>>
>>
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>>
>
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