[starpu-devel] [stencil based code: omitting last row and last column]

[Maxim Abalenkov <maxim.abalenkov@gmail.com>]

Dear all,

How are you? I hope all is well with you. I need help please. I’m introducing StarPU to a stencil based (finite difference) code. I’m facing a situation where I have to perform a two stage update over a 2D array. This 2D array is implemented as a 1D array in C. To divide this array into chunks for StarPU tasks I use a 1D ‘filter’:

// divide data array into blocks

struct starpu_data_filter block_filter {

    .filter_func = starpu_vector_filter_block,

    .nchildren = NBLOCKS,

};

I need to omit updating the boundary elements (last row and last column elements) of my array. Please see the figure attached. The top left grid depicts the first update stage where the last row needs omitting from the calculation. The bottom left grid shows the second update stage, where the last column of elements needs omitting. The shaded regions are the elements I need to skip.

My question is: does StarPU have helper routines to skip calculation in those regions? Maybe a 2D filter would help here? Otherwise, I will have to perform manual checks and convert local i,j indices in each block into global indices and skip calculation if the global index falls into a shaded region. Is there a way in StarPU to find out global ‘begin’ and ‘end’ indices of each block—the indices used internally by the ‘filter’ routine?

Thank you for your help and have a good day ahead! 

—

Best wishes,

Maxim

Maxim Abalenkov \\ maxim.abalenkov@gmail.com
+44 7 486 486 505 \\ www.maxim.abalenkov.uk