Spring Webflux - performance of event loop when only one core

A small question on Spring Webflux's performance, but on hardware with only one core.
I know, you might be asking, "why", or even "how in 2020, to run Springboot app on machine with only one core", or even something like "don't do that!"

My question is rather to gather some empiric data, founded theory and performance result.

Spring Webflux is well known to be non-blocking and use event loop (and not thread) in order to deal with IO, computation etc...

But what will happen if the event core is running on a machine with only just one core, will it be some kind of catastrophe? Maybe falling back to thread model? Or maybe the IO performance will be horrible and somehow regress to become blocking again?

Or maybe it will have no issue and the one core will still take care of everything fine, just performing all event loop feature back to itself?

Thank you

> But what will happen if the event core is running on a machine with only just one core, will it be some kind of catastrophe?

There is no "event core", just an "event loop" running on a standard thread. The event loop thread is (most likely in a single core setup) just a single thread that will be scheduled to run on the CPUs core like any other, but, as per the event loop model, that single thread will operate in a non-blocking manner, handling all the application's traffic.

> Maybe falling back to thread model? Or maybe the IO performance will be horrible and somehow regress to become blocking again?

There is no "falling back" to a thread model, and it wouldn't make much sense to do so. If you're struggling to run everything on your machine without the overhead of thread-per-request context switching, adding that context switching back in is never going to help.

(The only case where it would is where you have blocking operations on your event loop, but that's everything to do with a bug in your code and nothing to do with the overall system performance.)