[openib-general] cq polling order

[Devesh Sharma]

Hi, Dotan Thanks for quick reply.

On 8/7/06, Dotan Barak <dotanb at mellanox.co.il> wrote:
>
> Hi.
>
> On Monday 07 August 2006 10:06, Devesh Sharma wro
> > Hello everybody,
> > I have a query regarding cq poll concept.
> > Consider the following situation:
> >
> > Consumer has posted 2 SEND operations after that it posted 1 RDMA_READ
> > operation and againg 1 SEND operation ( Not posted with Barrier Fence,
> Is it
> > expected from consumer that it can post without Barrier Fence after RDMA
> > READ? ), now while polling in what order completions should be returned
> by
> > verbs?
> >
> > Is it expected by consumer that completions will be polled in posting
> order
> > or they can come out of order?
> > Polling order 2 SEND_COMP, 1 RDMA_READ_COMP, 1 SEND_COMP
> >  OR
> > Polling order 3 SEND_COMP, 1 RDMA_READ_COMP
> >
> > which is expected?
>
> The order the completions must be the same as the order of the WR that you
> posted to the Send Queue.
> so, you should expect the first option.


But RDMA Read  may complete out of order. Is it means that HCA Driver should
be implemented such that order is maintained in such situations?

as you mentioned, if the fence bit is enable on a specific SR, the HCA need
> to wait until all the previous SR
> will be finished (according to the fence laws in the IB spec ..).


If consumer is specifing Fence then there is No problem of polling order,
Since, HCA will not start processing next WR untill all WR prior to this WR
completes, Hence polling will inherently be done in order, But issue is if
Cosumer dose not uses FENCE flag in next send operation after RDMA READ.

Dotan
>
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