On Thu, Oct 01, 2015 at 11:03:01AM -0700, Paul E. McKenney wrote:

On Thu, Oct 01, 2015 at 07:13:04PM +0200, Peter Zijlstra wrote:

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On Thu, Oct 01, 2015 at 08:09:09AM -0700, Paul E. McKenney wrote:

quoted

On Thu, Oct 01, 2015 at 02:24:40PM +0200, Peter Zijlstra wrote:

quoted

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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.  ;-)

I suspect he is; but I'm not _that_ up to date on the whole C11 stuff.