Function attn_side_chunks 

pub fn attn_side_chunks(vd: usize, splits: usize) -> usize

The chunks of its row a block that holds them weighs side by side (lk_attn_side): as many as its threads’ value slots hold — each chunk vd / 2 pairs a head, a thread attn_values_per_thread a head — and no more than the row’s splits; one where a chunk fills them.