Re: [Xen-devel] RING_HAS_UNCONSUMED_REQUESTS oddness

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-03-11 at 23:24 +0000, Zoltan Kiss wrote:
> On 11/03/14 15:44, Ian Campbell wrote:

> > Is it the case that this macro considers a request to be unconsumed if
> > the *response* to a request is outstanding as well as if the request
> > itself is still on the ring?
> I don't think that would make sense. I think everywhere where this macro 
> is called the caller is not interested in pending request (pending means 
> consumed but not responded)

It might be interested in such pending requests in some of the
pathological cases I allude to in the next paragraph though?

For example if the ring has unconsumed requests but there are no slots
free for a response, it would be better to treat it as no unconsumed
requests until space opens up for a response, otherwise something else
just has to abort the processing of the request when it notices the lack
of space.

(I'm totally speculating here BTW, I don't have any concrete idea why
things are done this way...)


> > I wonder if this apparently weird construction is due to pathological
> > cases when one or the other end is not picking up requests/responses?
> > i.e. trying to avoid deadlocking the ring or generating an interrupt
> > storm when the ring it is full of one or the other or something along
> > those lines?



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