Re: CQEs in unreliable connection

[Dotan Barak <dotanba-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 29/11/2013 16:53, Anuj Kalia wrote:
> Dotan,
>
> In the example that I asked about, the 5 packets do not form one
> message - they are each individual messages. I assume this in the
> following.
>
> I now understand that packet reordering cannot happen in IB - thanks!
> Only packet loss can happen. From this, I can conclude the following
> (please correct me if I'm wrong somewhere):
>
> "If the requester sends a sequence of single packet messages: {M_1,
> M_2, ..., M_n}, then the sequence of packets at the responder will be
> {M_i1, M_i2, ..., M_ik}, where i1 < i2 < ... < ik. Which is just
> saying that messages can be lost, but not reordered."
>
> Is there a case where messages can be reordered in UC transport? i.e.
> if the requester issues an RDMA write to buf[0] followed by an RDMA
> write to buf[1], is it possible that at the responder the write to
> buf[1] is done before the write to buf[0]? I don't think that this is
> possible.
I assume that we are talking about a single QP.

The messages will be sent by the order they are sent:
the message that access buf[0] will be sent (and received by the 
receiver) before the message that access buf[1].

If you are talking about the way that the memory data is being written/seen
in the remote side. I'm throwing a wild guess here, but *maybe* your 
process can see
the new content in first buf[1] before buf[0] depends on the memory 
policy, NUMA location, etc...
(this isn't a zone that I have a lot of knowledge in, but I think that 
this may have affect).

Thanks
Dotan


>
> Thanks again. Your comments and blog have been really useful.
>
> --Anuj.
>
>

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