Messages in this thread | | | Date | Fri, 16 Mar 2007 10:58:51 +0100 | From | Ingo Molnar <> | Subject | Re: [Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console |
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* 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().
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