Re: [Xen-devel] RING_HAS_UNCONSUMED_REQUESTS oddness

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On 12/03/14 11:28, Ian Campbell wrote:
> 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.

Yes, I think this is true at least for blkback, when blkback starts
processing a request it assumes that a response slot will be available
in order to write the response when the request has finished processing.

Roger.


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