From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dotan Barak Subject: Re: CQEs in unreliable connection Date: Fri, 29 Nov 2013 22:30:54 +0200 Message-ID: <5298F97E.4030004@gmail.com> References: <52979E37.3080000@gmail.com> <52982D04.70503@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Anuj Kalia Cc: Hari Subramoni , "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-rdma@vger.kernel.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. > > -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html