On Tue, Nov 26, 2013 at 05:05:14PM -0800, Linus Torvalds wrote: > On Tue, Nov 26, 2013 at 4:39 PM, Paul E. McKenney > <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > Cross-CPU ordering. > > Ok, in that case I *suspect* we want an actual "spin_lock_mb()" > primitive, because if we go with the MCS lock approach, it's quite > possible that we find cases where the fast-case is already a barrier > (like it is on x86 by virtue of the locked instruction) but the MCS > case then is not. And then a separate barrier wouldn't be able to make > that kind of judgement. > > Or maybe we don't care enough. It *sounds* like on x86, we do probably > already get the cross-cpu case for free, and on other architectures we > may always need the memory barrier, so maybe the whole > "mb_after_spin_lock()" thing is fine. > > Ugh. Indeed! I don't know any way to deal with it other than enumerating the architectures and checking each. My first cut at that was earlier in this thread. 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>