On 16/3/07 09:58, "Ingo Molnar" <[EMAIL PROTECTED]> wrote: >> These mb()'s are pretty standard for lock-free producer/consumer >> rings. Write descriptor /then/ write the updated producer. Read the >> producer /then/ read any descriptors revealed by this new producer >> value. > > then use rmb()/wmb(). Rarely does a ring protocol truly need mb().
It's needed for writing data /after/ reading the consumer index that shows you have space to write. Looking through xenbus_comms.c I think all the barriers are correct except there is a spurious extra mb() in xb_read(), where there is a later rmb() which is sufficient by itself. All the others have a purpose. -- Keir - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
