Re: [RFC v2 4/7] powerpc: atomic: Implement xchg_* and atomic{,64}_xchg_* variants

[Paul E. McKenney]

On Thu, Oct 01, 2015 at 07:13:04PM +0200, Peter Zijlstra wrote:
> On Thu, Oct 01, 2015 at 08:09:09AM -0700, Paul E. McKenney wrote:
> > On Thu, Oct 01, 2015 at 02:24:40PM +0200, Peter Zijlstra wrote:
> 
> > > I must say I'm somewhat surprised by this level of relaxation, I had
> > > expected to only loose SMP barriers, not the program order ones.
> > > 
> > > Is there a good argument for this?
> > 
> > Yes, when we say "relaxed", we really mean relaxed.  ;-)
> > 
> > Both the CPU and the compiler are allowed to reorder around relaxed
> > operations.
> 
> Is this documented somewhere, because I completely missed this part.

Well, yes, these need to be added to the documentation.  I am assuming
that Will is looking to have the same effect as C11 memory_order_relaxed,
which is relaxed in this sense.  If he has something else in mind,
he needs to tell us what it is and why.  ;-)

							Thanx, Paul

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/