[lcof]

No it’s an interesting comment. This is not really about load, but about control flow: if goroutine is just spinning wild without going through any function prologue, it won’t even be aware of the synchronous preemption request. Asynchronous preemption (signal-based) is mainly (I say “mainly” because I am not sure I can say “only”) for this kind of situation.

I don’t have the link ready, but twitch had this kind of issue with base64 decoding in some kind of servers. The GC would try to STW, but there would always be one or a few goroutines decoding base64 in a tight loop for the time STW was attempted, delaying it again and again.

Asynchronous preemption is a solution to this kind of issue. Load is not the issue here, as long as you go through the runtime often enough.