In practice, you indeed yield often enough — there is no perfect formula I believe — so in loops or elsewhere where you are spending too much time doing one thing. You don’t need to do it perfectly, you just need to yield often enough to give other coros a fair chance at completion. Relying on the kernel is a bad idea; that’s where you lose on performance. Also, to do what you are suggestions would mean that you use many, many OS threads and the kernel somewhat manages them all in a pre-emptive fashion, and you don’t need to do it yourself; but that means you need to pay the context switching, memory footprint etc costs. It won’t scale and will be slow.