On Thu, 2008-06-12 at 09:07 -0600, Matthew Wilcox wrote: > On Thu, Jun 05, 2008 at 06:43:53PM +1000, Benjamin Herrenschmidt wrote: > > Note that the powerpc implementation currently clears the flag > > on spin_lock and tests it on unlock. We are considering changing > > that to not touch the flag on spin_lock and just clear it whenever > > we do a sync (ie, on unlock, on explicit mmiowb, and possibly even > > on readl's where we happen to do sync's). > > Your current scheme sounds like it's broken for > > spin_lock(a) > writel(); > spin_lock(b); > spin_unlock(b); > spin_unlock(a); Which is why we are considering changing it :-) But as Paulus said before, he did some measurement and we came to the conclusion that (pending more measurements on a wider range of HW) we may as well drop the whole scheme and make writel fully synchronous instead. Then, we can get some nice weakly ordered accessors and start adding them with appropriate explicit barriers to the hot path of perf. critical drivers we care about. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
