On Friday 07 September 2007 20:13:12 Nick Piggin wrote: > On Sunday 09 September 2007 03:48, Nick Piggin wrote: > > > There is some suggestion in the source code that non-temporal stores > > (movntq) are weakly ordered. But AFAIKS from the documents, it is ordered > > when operating on wb memory. What's the situation there? > > Sorry, it looks from the AMD document like nontemporal stores to wb > memory can go out of order.
Yes, that is how NT stores are defined. > If this is the case, we can either retain the sfence in smp_wmb(), or noop > it, and put explicit sfences around any place that performs nontemporal > stores... We do this already, but in most cases it doesn't matter anyways. We AFAIK do not rely on any ordering for copy_*_user for example. There are not that many users of nt so it's not a huge issue. > > Anyway, the lfence should be able to go away without so much trouble. You mean sfence? lfence in rmb is definitely needed. sfence on x86-64 is not strictly needed, but also shouldn't hurt very much so I always kept it in. -Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
