Those nodes in the queue have to come from somewhere and that is where the inefficiency lies. If you use SIMD gather instructions to fetch all the children of

Those nodes in the queue have to come from somewhere and that is where the inefficiency lies. If you use SIMD gather instructions to fetch all the children of a node, that is still going to be very inefficient on e.g. a Xeon. Each of those gather loads are likely to hit different cache lines, which are accessed only once and waste 7/8th of the memory bandwidth pulling them in. SIMD is also not going to help if you are memory bandwidth or latency bound, we're talking ~0.1 ops/byte here.