Very few system calls in the main loop. Not even close to being io bound, and as I said memory is all preallocated, so allocator efficiency isn't a factor. Edi

Very few system calls in the main loop. Not even close to being io bound, and as I said memory is all preallocated, so allocator efficiency isn't a factor. Edit: realized I didn't answer your question, I ran flamegraph both ways and it was completely dominated by tight vectorized loops and a couple sadly necessary memory copies.