On Sat, Feb 28, 2015 at 10:45:33PM +0100, Peter Zijlstra wrote: > On Sat, Feb 28, 2015 at 09:36:15PM +0100, Manfred Spraul wrote: > > +/* > > + * Place this after a control barrier (such as e.g. a spin_unlock_wait()) > > + * to ensure that reads cannot be moved ahead of the control_barrier. > > + * Writes do not need a barrier, they are not speculated and thus cannot > > + * pass the control barrier. > > + */ > > +#ifndef smp_mb__after_control_barrier > > +#define smp_mb__after_control_barrier() smp_rmb() > > +#endif > > Sorry to go bike shedding again; but should we call this: > > smp_acquire__after_control_barrier() ? > > The thing is; its not a full MB because: > > - stores might actually creep into it; while the control dependency > guarantees stores will not creep out, nothing is stopping them from > getting in; > > - its not transitive, and our MB is defined to be so. > > Oleg, Paul? The idea is that this would become a no-op on x86, s390, sparc &c, an isb instruction on ARM, an isync instruction on Power, and I cannot remember what on Itanium? The other idea being to provide read-to-read control ordering in addition to the current read-to-write control ordering? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html