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    SubjectRe: [Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console

    * Keir Fraser <Keir.Fraser@xensource.com> wrote:

    > On 16/3/07 08:54, "Ingo Molnar" <mingo@elte.hu> wrote:
    >
    > >> + prod = intf->in_prod;
    > >> + mb();
    > >> + BUG_ON((prod - cons) > sizeof(intf->in));
    > >
    > > such mb()'s are typically a sign of "i have no clear idea what SMP
    > > serialization rules apply here, but something is needed because
    > > otherwise it breaks" ?
    >
    > 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().

    Ingo
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