Re: [Xen-devel] [PATCH 6/7] mini-os: Added rmb to xenbus code

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-06-06 at 17:10 +0200, Samuel Thibault wrote:
> Ian Campbell, le Fri 06 Jun 2014 15:15:42 +0100, a Ãcrit :
> > On Fri, 2014-06-06 at 05:59 +0100, karim.allah.ahmed@xxxxxxxxx wrote:
> > > In any case, by looking at the patch it seems like rmb was required to
> > > make sure that the reply message is visible to the current processor
> > > when this thread wakes up and starts reading it.
> > 
> > Can we assume (or arrange) that schedule() gives us this guarantee? Do
> > we want to?
> 
> I'd tend to think something like that, yes. More precisely, thread
> wait/wake primitives usually provide a barrier: events before the wake
> are supposed to complete before the wait returns. So both should have a
> memory barrier.

Makes sense to me.

Ian.


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