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

Andrea Parri
2018-06-25T12:29:03Z

On Mon, Jun 25, 2018 at 01:12:45PM +0100, David Howells wrote:
> 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.

RELEASE and ACQUIRE are not enough in SB. Can you elaborate?

Andrea

>
> David