Justifying sched_yield() in the RTS

[Niklas Hambüchen]

There are more related updates in https://gitlab.haskell.org/ghc/ghc/issues/9221, also including a short discussion of Linus's post.

Simon Marlow's overall response was:

> I'm very supportive of making this better, but as usual I will require thorough data to back up any changes :)
>
> Everything I tried in the past made things worse. Including an experiment I did to use futexes directly: https://gitlab.haskell.org/ghc/ghc/issues/3553?cversion=0&cnum_hist=14#note_39009

So it sounds like this topic is currently in the stage of:

Somebody needs to take the time to re-do that benchmark done 10 years ago.