On Tue, Oct 20, 2015 at 04:34:51PM -0700, Paul E. McKenney wrote: > There is also the question of whether the barrier forces ordering > of unrelated stores, everything initially zero and all accesses > READ_ONCE() or WRITE_ONCE(): > > P0 P1 P2 P3 > X = 1; Y = 1; r1 = X; r3 = Y; > some_barrier(); some_barrier(); > r2 = Y; r4 = X; > > P2's and P3's ordering could be globally visible without requiring > P0's and P1's independent stores to be ordered, for example, if you > used smp_rmb() for some_barrier(). In contrast, if we used smp_mb() > for barrier, everyone would agree on the order of P0's and P0's stores. Oh!? > There are actually a fair number of different combinations of > aspects of memory ordering. We will need to choose wisely. ;-) > > My hope is that the store-ordering gets folded into the globally > visible transitive level. Especially given that I have not (yet) > seen any algorithms used in production that relied on the ordering of > independent stores. I would hope not, that's quite insane. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
