Thanks for the clarification. My experience with system level IO calls is limited. I formed my answer from my experience and the Bert Belder talk I linked to ab

Thanks for the clarification. My experience with system level IO calls is limited. I formed my answer from my experience and the Bert Belder talk I linked to above. He actually describes libev as a wrapper around select, and says that select is slow but he does clarify in his slides that libev also uses epoll/kqueue, which I didn't notice until returning to the talk after your comment.