[ViennaCL-devel] Unintended behavior in fast_copy(cpu_matrix_begin, cpu_matrix_end, gpu_matrix) ?

[Philippe T. <phi...@gm...>]

Hello everybody !

Browsing through the internals, I have found :

    template <typename SCALARTYPE, typename F, unsigned int ALIGNMENT>

    void fast_copy(SCALARTYPE * cpu_matrix_begin,

                   SCALARTYPE * cpu_matrix_end,

                   matrix<SCALARTYPE, F, ALIGNMENT> & gpu_matrix)
Might not have the intended behavior : it reallocs the internal
gpu_buffer of gpu_matrix to a buffer of size
(cpu_matrix_end-cpu_matrix_begin)*sizeof(SCALARTYPE) , and copies the
data.


A user might however want to copy just a part of the cpu_matrix to the
gpu. Plus, reallocating the matrix without changing its sizes sounds a
bit weird.

Instead, wouldn't it be more intuitive to call clEnqueueWriteBuffer,
and to create an additional constructor : matrix(size1, size2,
cpu_matrix_begin) , which would indeed allocate with CL_COPY_HOST_PTR
flag.


Plus, such a constructor covers a special const-correctness case i've
faced : Creating a gpu matrix from cpu data, but not writing them
back. In that case, the gpu_matrix is const but it is not possible to
call fast_copy on it !

Best regards,
Philippe