[pca006132]

Probably doesn't make sense. Busy wait is fast when you can dedicate a core to the task, but this means that you cannot have many tasks in parallel with a small set of physical cores. When you oversubscribe, performance will quickly degrade.

Tokio and other libraries such as pthread allows thread to wait for something and wake up that particular thread when the event occurs. This is what allows scheduler to schedule many tasks to a very small set of cores without running useless instructions checking for status.

For foundational library, I think you want things that are composable, and low latency stuff are not that composable IMO.

Not saying that they are bad, but low latency is something that requires global effort in your system, and using such library without being aware of these limitations will likely cause more harm than good.