[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [DOC v2] Xen transport for 9pfs
On Mon, Dec 05, 2016 at 05:33:23PM -0800, Stefano Stabellini wrote: [...] > ## Xenstore > > The frontend and the backend connect via xenstore to exchange > information. The toolstack creates front and back nodes with state > [XenbusStateInitialising]. The protocol node name is **9pfs**. > > Multiple rings are supported for each frontend and backend connection. > It would help if you can state if a specific node is mandatory or optional. > ### Frontend XenBus Nodes > ### Backend XenBus Nodes [...] > The producer always notifies the consumer after incrementing **prod**. > However in some circumstances the producer is allowed not to notify the > consumer, just as a performance improvement, and still maintain > correctness. These are the steps to do it: after incrementing *prod*, > the producer reads *cons* a second time; if the value is changed from > the previous read and it is different from *prod* before the update, > then the notification can be avoided. These are the producer steps, with > the optimization: > > - read *prod* (old_prod), *cons* (old_cons) from shared memory > - general memory barrier > - verify *prod* against local copy (consumer shouldn't change it) > - write to array at position *prod* up to *cons*, wrapping around the circular > buffer when necessary > - write memory barrier > - increase *prod* (new_prod) > - general memory barrier > - read *cons* (new_cons) > - if new_cons == old_cons or new_cons == old_prod, then notify the > consumer > I think it would be valuable to extract this section to a generic "how to write driver" doc. But that's probably something for another day. Wei. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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