Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees

David Howells
2018-06-25T12:12:53Z

Peter Zijlstra <peterz@infradead.org> wrote:

> So yes, I suppose we're entirely suck with the full memory barrier
> semantics like that. But I still find it easier to think of it like a
> RELEASE that pairs with the ACQUIRE of waking up, such that the task
> is guaranteed to observe it's own wake condition.
>
> And maybe that is the thing I'm missing here. These comments only state
> that it does in fact imply a full memory barrier, but do not explain
> why, should it?

I think because RELEASE and ACQUIRE concepts didn't really exist in Linux at
the time I wrote the doc, so the choices were read/readdep, write or full.

Since this document defines the *minimum* you can expect rather than what the
kernel actually gives you, I think it probably makes sense to switch to
RELEASE and ACQUIRE here.

David