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xen-devel
Re: [Xen-devel] Why are I/O rings bidirectional?
I think the intended question was "why have both requests and responses
in the same ring rather than have two rings, one for requests and one
for responses?"
On Mon, 2005-02-07 at 23:00 +0000, Mark Williamson wrote:
> > Hello. I am reading Xen and the Art of Virtualization. I am curious as
> > to why the async I/O ring buffers contain both requests and responses
> > in the same ring.
>
> Requests contain details of the IO to be done. Responses notify the domain
> when the IO is complete and whether it was successful or not.
>
> Requests can complete out of order, so it's necessary to have response
> messages following back to the domain to tell it when each request is done.
> If the requests were always dealt with in order it would not be necessary to
> have responses flowing back, so the ring could be unidirectional.
>
> The Safe Hardware Access paper has more details about the IO rings work.
>
> HTH,
> Mark
>
>
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--
Harry Butterworth <harry@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
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