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What Mike is saying about the banking and column-wise relationship is true. However, if you are just iterating over the entire array by accessing consecutive elements, my money would be on the row-by-row access pattern. If you iterate over the entire row elements and unroll this loop, the compiler will merge the consecutive accesses into very efficient wider accesses.
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Ok, I should point out that for this to work, unrolling the column loop is key; this creates consecutive accesses that compiler can merge.
e.g.
for(row = 0; row < N; row++) {
# pragma unroll
for(col = 0; col < 4; col++) {
A[row][col] = row + col;
}
}
This essentially creates:
for(row = 0; row < N; row++) {
A[row][0] = row;
A[row][1] = row + 1;
A[row][2] = row + 2;
A[row][3] = row + 3;
}
which gets translated to smth like this
for(row = 0; row < N; row++) {
A[row][0] = (int4)( row, row+1, row+2, row+3 ); // very efficient wide access
}
I think this is mentioned in the best practices guide document.
Honored Contributor
