On Mon, Jun 25, 2018 at 02:28:50PM +0200, Andrea Parri wrote: > On Mon, Jun 25, 2018 at 01:12:45PM +0100, David Howells wrote: > > Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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? I prefer RELEASE vs wait-condition and treat task->state as an internal matter. Also note how the set_current_task() comment is fairly vague on what exact barriers are used. It just states 'sufficient'. Maybe I should just give up and accept smp_mb(), but strictly speaking that is overkill, but it is the only sufficient barrier we currently have. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
