>>>>> "Nick" == Nick Piggin <npiggin@xxxxxxx> writes: Nick> mb and wmb are now no longer guaranteed to order system memory Nick> operations with device memory stores. mmiowb has been introduced Nick> to provide this ordering (when combined with a mb, wmb, or Nick> spin_unlock). Unfortunately, it appears to be rather less well Nick> understood among both users and implementors than even the old Nick> memory barrier scheme. It also subtly breaks existing code that Nick> uses mb or wmb (if only on sn2). I really think it is not a good Nick> solution. Nick> The alternative I propose is to restore mb and wmb to their full Nick> strength. This does mean that sn2 has to do the equivalent of Nick> mb+mmiowb, wmb+mmiowb respectively, but that's the price you pay Nick> for weak memory ordering. Nick, Introducing this constraint would make me less than pleased I have to admit. It's a very expensive operation to do since it requires going out talking to the PCI bridge, doing that on every wmb() is going to really hurt :-( Cheers, Jes -- 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
