* H. Peter Anvin <hpa@xxxxxxxxx> wrote: > On 12/19/2013 08:21 AM, Peter Zijlstra wrote: > > > > What's that mb for? > > > > It already exists in mwait_idle_with_hints(); I just moved it into > this common function. It is a bit odd, I have to admit; it seems > like it should be *before* the monitor (and possibly we should have > one after the CLFLUSH as well?) Yes, I think we need a barrier before the CLFLUSH, because according to my reading of the Intel documentation CLFLUSH has no implicit ordering so it might get reordered with the store to ->flags in current_set_polling_and_test(), which might result in spurious wakeup problems again. (And CLFLUSH is a store in a sense, so special in that the regular ordering for stores does not apply.) Likewise, having a barrier before the MONITOR looks sensible as well. Having it _after_ monitor looks weird and is probably wrong. [It might have been the effects of someone seeing the spurious wakeup problems with realizing the true source, or so.] Thanks, Ingo -- 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