On Wed, Apr 03, 2013 at 09:33:48AM -0700, Paul E. McKenney wrote: > On Wed, Apr 03, 2013 at 06:45:51AM -0700, Ian Lance Taylor wrote: [ . . . ] > > If using a sufficiently recent version of GCC, you can get the > > behaviour that I think you want by using > > __atomic_load(&x, __ATOMIC_RELAXED) > > If this maps to the memory_order_relaxed token defined in earlier versions > of the C11 standard, then this absolutely does -not-, repeat -not-, work > for ACCESS_ONCE(). The relaxed load instead guarantees is that the load > will be atomic with respect to other atomic stores to that same variable, > in other words, it will prevent "load tearing" and "store tearing". I > also believe that it prevents reloading ... In addition, even if the semantics of relaxed loads now guarantee against load combining, note that ACCESS_ONCE() is also used to prevent combining and splitting of stores, for example: ACCESS_ONCE(p) = give_me_a_pointer(); Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>