> It seems reasonable to ask people to learn that locks have stronger > ordering guarantees than RMW atomics do. Maybe not the greatest > situation in the world, but one I think we could live with.
Yeah, this was one of my main objections. > > Hence my proposal to strenghten rmw-acquire, because that is the basic > > primitive used to implement lock. > > That was essentially what the v2 patch did. (And my reasoning was > basically the same as what you have just outlined. There was one > additional element: smp_store_release() is already strong enough for > TSO; the acquire is what needs to be stronger in the memory model.) Mmh? see my comments to v2 (and your reply, in part., the part "At least, it's not a valid general-purpose implementation".). > > Another, and I like this proposal least, is to introduce a new barrier > > to make this all work. > > This apparently boils down to two questions: > > Should spin_lock/spin_unlock be RCsc? > > Should rmw-acquire be strong enough so that smp_store_release + > rmw-acquire is RCtso? > > If both answers are No, we end up with the v3 patch. If the first > answer is No and the second is Yes, we end up with the v2 patch. The > problem is that different people seem to want differing answers. Again, maybe you're confonding v2 with v1? Andrea > > (The implicit third question, "Should spin_lock/spin_unlock be RCtso?", > seems to be pretty well settled at this point -- by Peter's and Will's > vociferousness if nothing else -- despite Andrea's reservations. > However I admit it would be nice to have one or two examples showing > that the kernel really needs this.) > > Alan >
